Changes in Renal Blood Flow and Possibly the Intrarenal Distribution of Blood During the Natriuresis Accompanying Saline Loading in the Dog

Changes in Renal Blood Flow and Possibly the Intrarenal Distribution of Blood during the Natriuresis Accompanying Saline Loading in the Dog

Laurence E. Earley, Robert M. Friedler

J Clin Invest. 1965;44(6):929-941. https://doi.org/10.1172/JCI105210.

Research Article

Find the latest version: https://jci.me/105210/pdf Journal of Clinical Investigation Vol. 44, No. 6, 1965

Changes in Renal Blood Flow and Possibly the Intrarenal Distribution of Blood during the Natriuresis Accom- panying Saline Loading in the Dog * LAURENCE E. EARLEY t AND ROBERT M. FRIEDLER (From the Thorndike Memorial Laboratory, Second and Fourth [Harvard] Medical Services, Boston City Hospital, and the Department of Medicine, Harvard Medical School, Boston, Mass.)

Several recent studies have provided evidence ing limb of Henle's loop, resulting in the delivery that the increased excretion of sodium associated of a larger volume of fluid of lower sodium con- with expansion of the extracellular volume may centration to the transport sites of the ascending result in part from factors other than an increase limb of the loop. The present studies were under- in the filtered load of sodium. In the dog receiving taken to determine if a relationship could be dem- a mineralocorticoid, the infusion of isotonic saline onstrated between changes in the tubular reabsorp- may be accompanied by increased excretion of so- tion of sodium and changes in renal blood flow. dium without a spontaneous increase in the filtered It was observed that the increased excretion of so- load of sodium (1, 2). During saline loading glo- dium during isotonic expansion of the extracellular merular filtration rate (and filtered sodium) may volume was uniformly associated with increased be reduced experimentally without abolishing the renal blood flow, independent of spontaneous saline-induced natriuresis (1, 3-6). Thus, a large changes in glomerular filtration rate. Further- body of evidence is consistent with the concept more, changes in the net tubular reabsorption of that expansion of the extracellular volume in the sodium, which were demonstrated both spontane- dog results in a net decrease in the tubular reab- ously during the course of saline loading and dur- sorption of sodium, independent of changes in the ing controlled unilateral reductions of renal blood tubular effects of aldosterone. In a recent study flow, were associated with inverse changes in that from this laboratory it was demonstrated that this portion of renal plasma flow from which p-amino- decreased net tubular reabsorption of sodium that hippurate (PAH) is not extracted. accompanies saline loading may be associated with a decrease in urinary osmolality that is not ac- Methods by changes in either antidiuretic hor- counted for Twenty-eight mongrel dogs of either sex, ranging in mone activity or solute excretion (6). On the basis weight from 13.2 to 21.3 kg, were deprived of food and of this latter observation it was suggested that sa- water for 20 hours before experiments. Approximately line loading in the dog may result in an increased 4 hours before experiments the animals received by in- renal medullary blood flow which decreases medul- tramuscular injection 5 U of Pitressin Tannate in oil lary interstitial hypertonicity, and that decreased and 5 mg of DOCA (,desoxycorticosterone acetate) in oil. Under light pentob4rbital anesthesia the right ureter medullary interstitial hypertonicity may decrease was exposed through a flank incision and cannulated with net sodium reabsorption secondarily by diminishing polyethylene tubing. The left kidney and ureter were the passive reabsorption of water from the descend- exposed through a subcostal incison, and the left ureter was simlarly cannulated. With minimal dissection the * Submitted for publication August 17, 1964; accepted left spermatic or ovarian vein was exposed at its en- February 18, 1965. try into the renal vein. An 18-gauge needle containing a Aided in part by grants AM-5401-03 from the National plastic catheter (2 mm o,d.) was inserted into the ovarian Institutes of Health, and NsG595 from the National Aero- or spermatic vein and dltected toward the kidney. The nautics and Space Administration. plastic catheter was then inserted 2 to 3 cm along the t Fellow of the Boston Medical Foundation. Address renal vein in the direction of the kidney, the needle was requests for reprints to Dr. Laurence E. Earley, Thorn- removed, and the catheter was tied tightly in place at its dike Memorial Laboratory, Boston City Hospital, 818 entry into the spermatic or ovarian vein. The position of Harrison Avenue, Boston, Mass. 02118. the catheter in the direction of the kidney was always 929 930 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER

TABLE I Renal hemodynamic changes during saline loading*

GFR CPAH EPAit RBF NCPF UNaV mi/min mlminm/1min ml/min IAEq/min Control 40 ± 14 126 1t 49 0.786 + 0.072 261 i 76 32 i 10 97 i 83 Saline load 49 ± 15 195 i 70 0.635 i: 0.149 425 i 120 116 i 54 1,075 i 538 *Values are the means and standard deviations for the left kidney from 28 experiments. Abbreviations: GFR = glomerular filtration rate, CPAH = clearance of p-aminohippurate, EPAH = extraction ratio for p-aminohippurate, RBF = total renal blood flow, NCPF = "noncortical plasma flow" (renal plasma flow - CPAH), and UNaV = rate of sodium excretion. t Includes two experiments with Diodrast-113 instead of p-aminohippurate. made certain by observing the movement of minute in- wounds, 60 to 90 minutes was allowed before beginning jected air bubbles along the renal vein. The venous experimental measurements. A plastic catheter inserted catheter was kept patent by the infusion of 0.4% saline into the lower aorta through a femoral artery was used at 0.2 to 0.3 ml per minute. In 16 experiments, either to collect arterial blood samples and to measure arterial tape or a Blalock clamp was placed around the aorta be- pressure. tween the renal arteries and carried out of the body wall. Eighty to 100 minutes before experimental measure- This allowed reversible constriction of the aorta above ments, an infusion of isotonic saline was begun at a fixed the left renal artery. After closure of the surgical rate between 0.25 and 0.30 ml per minute. (In eight experiments with aortic constriction this maintenance infusion was delivered at 1.5 ml per minute.) This infusion DIODRASI delivered PAH at 2.5 to 3.5 mg per minute, creatinine or .85 inulin at approximately 12 or 10 mg per minute respec- tively, vasopressin at 40 to 60 mU per kg per hour, and .75 desoxycorticosterone at 25 ,tg per minute. The solution .65 was acidified to pH 5.0 to 5.5 with acetic acid. In five EXTRACTION experiments the maintenance infusion contained either RATIO .55 Diodrast-I"3' or Hippuran-I'3'1 in tracer amounts to de- liver 0.25 to 0.50 ,lc per minute. In two experiments the .45 maintenance solution contained Diodrast-I.3. but no PAH. At the mid-point of each urine collection, arterial and .35 renal venous blood samples were collected simultaneously into heparinzed syringes and transferred immediately to .25 ° Contro/l. ice-packed tubes. The blood samples were centrifuged * Saline Load immediately at 4 to 5° C for exactly 5 minutes. The total elapsed time from beginning blood sampling to the 700 separation of plasma was uniform in all experiments and did not exceed 10 minutes. RENAL 600 After three or four control collections each animal re- BLOOD FLOW ceived a modified Ringer's solution (Na 145, K 3.5, Cl 500 128.5, HCO3 20 mEq per L; hereafter referred to as sa- mL/min line) at a rate of 50 ml per minute, until a total of 1,250 400 to 1,750 ml (80 to 120 ml per kg) was infused. This loading infusion was then continued at a rate approxi- 300 mately the same as the rate of urine flow. Three to five II collections were made during the saline diuresis. Five 200 of the experiments were concluded at this point. In seven experiments the infusion of saline was then discontinued, and when the rate of urine flow had decreased to approxi- FIG. 1. CHANGES IN RBF AND EPAH OR EDIODRAST mately 1 ml per minute, three or four additional collec- DURING SALINE LOADING. Points represent the means of tions were made. three or more consecutive and uniform collection periods In 16 experiments after collections during the main- from the left kidney only. The first two experiments on tained diuresis, the aorta was constricted between the re- the left were performed with Diodrast-I' in the absence nal arteries to reduce the flow of urine from the left of PAH. All other extraction ratios are for PAH. Dur- kidney. In seven experiments the aortic constriction was ing the control measurements sodium excretion averaged performed in two stages. Urine flow was first reduced 97 ,uEq per minute per kidney and during saline loading to 40 to 60%o of the diuretic rates (aortic pressure, 70 to increased to an average of 1,075 ,uEq per minute per kidney (see text). 1 Abbott Laboratories, Oak Ridge, Tenn. RENAL HEMODYNAMICS DURING SALINE LOADING 931

85 mm Hg). After collecting three to five periods, addi- termined by the Jaffe reaction as described by Kennedy, tional constriction was applied to reduce urine flow to Hilton, and Berliner (7), or as modified for the Techni- rates 0.5 to 2.0 ml per minute greater than the presaline con autoanalyzer (8); inulin by the method of Walser, infusion control values (aortic pressure, 40 to 60 mm Hg). Davidson, and Orloff (9); PAH by a modification of the After collecting three to six periods the aortic constriction method of Smith and his associates (10), or as modified was released, and collections were continued. In nine ex- for the Technicon autoanalyzer (8); sodium by internal periments, only the more extensive aortic constriction standard flame photometry; and hematocrits by centri- was applied. In eight of the experiments employing aortic fugation in standard Wintrobe tubes. Diodrast-Im and constriction the animals received 200 or 300 ml of iso- Hippuran-I' radioactivty were measured in a well type tonic saline 3 hours before beginning experimental col- scintillation counter.8 lections. In these eight experiments the maintenance in- The renal extraction ratios (E) of PAH, Diodrast, and fusion (creatinine, PAH, and so forth in isotonic saline) Hippuran were calculated from the formula, E = (A-R) / was delivered at 1.5 ml per minute instead of 0.25 to 0.30 A, where A is the arterial and R the renal venous con- ml per minute.2 In 12 of these experiments arterial pres- centrations of the extracted substance. Total renal plasma sure was recorded from the aorta, below the renal ar- flow (RPF) was calculated as CPAH/EPAH, or (in experi- teries, with a Sanborn pressure transducer and model ments with extraction ratios less than .5) from the for- 964 recorder. mula of Wolf (11). RPF = [V (U-R)]/[A-R], where Clearance calculations were not made from transitional V = rate of urine flow and U = the urinary, R = the re- periods during saline loading, during the subsiding diu- nal venous, and A = the arterial concentrations of the resis following saline loading, or immediately following extracted substance. Total renal blood flow (RBF) was constriction or release of the aorta. Creatinine was de- calculated from RPF and the hematocrit (Hct): RBF = RPF/ (l -.95 Hct). 2 This preloading with a relatively small volume of sa- In the present calculations of E and RPF no correc- line and the higher rate of maintenance infusion did not tions have been made for the estimated diffusion of the impair the large hemodynamic and natriuretic responses to extracted substance from red blood cells the experimental saline load. However, this procedure (12). With CPAH assumed to approximate renal cortical resulted in higher control rates of glomerular filtration plasma flow, "noncortical plasma flow" (NCPF) was calculated as rate (GFR) and clearance of PAH (CPAH) and some- RPF - CPAH. what smaller increases in these measurements during the saline load. 3 Nuclear-Chicago, Des Plaines, Ill.

TABLE II The effects of transient saline loading on renal hemodynamics and sodium excretion*

V GFR CPAH RBFt UNaV FNa -Extraction Hema- R L R L R L ratio R L R L R L PNa tocrit ml/min mil/min ml/min ml/min Eql/min ;&Eq/min mEqIL 1. Control 0.17 0.17 36 38 114$ 119$ .831t 219 228 36 35 5,005 5,290 139 40 Saline loading 6.60 2.82 51 47 254t 258$ .680t 494 501 1,082 476 7,100 6,545 139 26 Postload 1.41 0.97 51 52 119$ 118t .785t 241 239 273 190 6,990 7,120 137 38 2. Control 0.42 0.47 37 37 94 96 .810 199 197 79 100 5,165 5,165 140 42 Saline loading 3.98 5.46 47 49 163 166 .741 298 304 720 946 6,620 6.905 141 28 Postload 1.16 1.50 50 54 139 145 .805 278 285 269 349 6,800 7,350 136 39 3. Control 0.23 0.24 37 43 103 116 .835 232 260 59 58 5,360 6,240 145 50 Saline loading 6.18 5.80 49 52 192 211 .701 419 460 1,107 1,062 6,955 7,390 142 36 Postload 0.74 0.81 46 52 88 100 .843 180 205 187 198 6,160 6,970 134 44 4. Control 0.17 0.25 34 36 85 93 .825 171 187 40 43 5,065 5,412 149 42 Saline loading 4.74 6.98 42 47 116 130 .786 176 217 910 1,263 6,050 6,770 144 25 Postload 1.56 1.78 39 44 96 105 .840 164 180 384 409 5,695 6,420 146 32 5. Control 0.21 0.19 46 42 169 146 .826 305 268 34 32 6,660 6,095 145 35 Saline loading 4.32 4.65 @0 250 246 .669 478 471 817 869 9,150 8,575 143 23 Postload 1.80 1.70 62 57 171 156 .830 297 269 415 388 8,560 7,870 138 31 6. Control 0.13 23 74 .683 181 23 3,405 148 42 Saline loading 9.85 8.37 38 35 105 108 .637 224 231 1,320 1,101 5,620 5,180 148 28 Postload t.22 0.87 30 31 63 71 .756 133 152 233 157 4,410 4,560 147 39 7. Control 0.63 0.41 32 32 80 82 .673 196 195 107 74 4,390 4,390 137 40 Saline loading 3.46 4.76 33 38 115 126 .529 278 303 491 619 4,555 5,250 138 23 Postload 1.21 1.33 29 31 73 75 .696 170 175 178 202 3,945 4,215 136 40

* Values for the left kidney are the means of usually three uniform consecutive collection periods; those for the right kidney are usually a single collection over the same period of time. Control observations ranged from 30 to 80 minutes; saline loading observations were made during 30 to 90 minutes immediately after completing a 1,500- to 1,750-mI infusion; postload observations were made over a period of 30 to 60 minutes beginning 45 to 90 minutes after discontinuing the infusion of saline. Additional abbreviations: V = rate of urine flow, FNa = filtered sodium, and PNa = plasma sodium concentration. t RBF for each kidney calculated from extractions measured from left kidney. t Clearance and extraction ratio for Diodrast-1131; all other clearances and extraction ratios are for PAH. 932 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER

Control 'SA4L INE , Post-Lood Results it LOADa The of saline loading on renal blood flow .80 \0 effects DIODRAST-I31 />0 and extractions of PAH, Diodrast, and Hippuran. EXTRACTION .70 RATIO In a total of 28 experiments extraction ratios were .60 measured and renal blood flow was calculated from collections before saline loading and during the diuresis accompanying a maintained saline load. These results are summarized in Table I and Figure 1. The renal extraction of PAH, Diodrast, or Hippuran decreased in every experiment, with an average absolute fall of 15.1%o (range, 3.9 to 33.7%o ). In the 28 experiments, EPAH (or EDiodrast) before saline loading averaged 0.786 + .072 (SD) and during saline loading averaged FILTERED 0.635 +.149. RBF increased from a mean of SODIUM 261 + 76 ml per minute per kidney to a mean of .Eq/min 425 120 ml per minute per kidney. Even though minimal increases in RBF occurred in some experiments, EPAH was always decreased during saline loading (Figure 1). RPF increased by a mean of 153 ml per minute with an increase in noncortical plasma flow (see Methods) of 84 ml FIG. 2. CHANGES IN SODIUM EXCRETION, FILTERED SO- of sodium in these DIUM, RBF, AND EDIODRAST DURING THE TRANSIENT COURSE per minute. The excretion OF NATRIURESIS ACCOMPANYING SALINE LOADING. Con- experiments increased from a control mean of 97 secutive collection periods from the left kidney are shown. juEq per minute per (left) kidney (range, 6 to The periods during rapid saline loading and immediately 238) to a mean of 1,075 /%Eq per minute per kidney after discontinuing the infusion of saline are not in- (range, 313 to 2,412) during the maintained saline cluded. Elapsed time is from the beginning of the first load (Table I). control collection. In this experiment GFR and filtered Relationship between sodium excretion and sodium continued to increase as sodium excretion di- and sodium. In seven ex- minished during the postloading period. PAH was not RBF, EPAH, filtered infused in this experiment. Changes in sodium excretion periments measurements were made before, during, correlated closely with changes in RBF and EDIodrast. and after saline loading (Table II). In all seven The scale for filtered sodium is four times that for so- of these experiments GFR and filtered sodium in- dium excretion. creased during saline loading, as RBF increased

TABLE III Effects of saline loading on renal hemodynamics and sodium excretion in the absence of spontaneous increases in filtered sodium

V GFR CPAH RBF UNaV FNa ilema- R L R L R L EPAH R* L R L R L PNa tocrit ml/min ml/min ml/min ml/min A&Eq/min 1iEq/min mEq/L 8. Control 0.11 0.17 19t 23t 49 62 .620 136 197 4 6 2,678 3,360 146 44 Saline loading 3.54 4.40 19t 20t 51 53 .291 216 230 529 560 2,579 2,810 141 20 9. Control 0.49 0.32 38 36 120 117 .810 250 253 128 87 5,548 5,183 146 43 Saline loading 6.60 6.17 37 33 134 137 .531 335 344 898 755 5,402 4,838 146 26 10. Control 0.98 1.05 47 47 110 113 .774 201 162 217 233 6,746 6,746 143 31 Saline loading 8.25 8.05 49 48 153 150 .556 348 355 1,273 1,180 6,958 6,804 143 22 11. Control 0.85 0.95 37 50 99 124 .710 224 281 139 199 5,365 7,155 145 40 Saline loading 5.34 7.19 32 45 108 145 .434 339 454 847 1,110 5,616 6,493 145 28 12. Control 0.97 0.65 66 63 229 240 .825 394 407 188 161 9,438 8,937 143 31 Saline loading 5.32 2.97 64 61 286 285 .780 469 468 798 613 9,088 8,590 142 23

* Blood flow calculated from extractions measured from left kidney. t Clearance of inulin; all other measurements of GFR are clearances of exogenous creatinine. RENAL HEMODYNAMICS DURING SALINE LOADING 933

I'm,, I I--- I ing, despite striking increases in the excretion of Control SALINE LOAD,I .,I sodium (Table III). In these experiments EPAH was reduced and RBF increased during saline PAHM 80 EXTRACTION loading, as in all other experiments. Also, in RATIO .70 these five experiments CPAiI during saline loading .6C was either not increased or increased less than the average increase for all experiments. Thus, in .50 these five experiments no increase in filtered sodium accompanied the natriuretic response to saline loading, yet the usual decrease in EPAH and RENAL 40C BLOOD FLOW increase in RBF were present during saline load- 30C mL/min _1 ing. Consecutive collection periods from one of 20C these experiments are shown in Figure 3. Therefore, in the 12 studies summarized in 0 1 II III, changes in sodium excretion o~ Tables and .----- (related to saline loading) correlated directly with SODIUM 80C0 EXCRETION FSOTERED changes in RBF and inversely with changes in jtEq/min 6010 ).Eq/min EpAH, but did not correlate directly with the spon- _ 5500 taneous changes in GFR and filtered sodium. 40(D 0 . s hemo- 0 :000 Effects of reduced blood flow on renal %% 0 20(01 0. * dynamics and sodium excretion. In a total of 16 experiments blood flow to the left kidney was re- 10 20 30 40 90 100 110 MINUTES FIG. 3. RENAL HEMODYNAMICS DURING SALINE LOAD- .85 ING WITHOUT A SPONTANEOUS RISE IN FILTERED SODIUM. Consecutive collections from left kidney are shown, ex- PAH .75 I1 I cept that the transition period during inital saline load- EXTRACTION ing is not included. Sodium excretion increased strikingly RATIO .65 I during saline loading despite decreases in the filtered load I I- of sodium. Accompanying this increased excretion of .55 I sodium was a rise in renal blood flow and a fall in the I extraction of PAH. 45 I o Saline Lood Saline Load ' and EPAH decreased. However, after the infusion 0 Aortic Constriction of saline had been discontinued and the diuresis allowed to subside, changes in GFR and filtered 700 sodium were unpredictable. In five of the seven 600 in studies the decrease filtered sodium was insuffi- RENAL 500 cient to account for the fall in excreted sodium BLOOD FLOW It following the saline load. In three studies GFR mL/min 400 either remained maximal or continued to increase 300 ir at.a time when the saline-induced natriuresis had -j 1{ I largely subsided (first three experiments, Table 200 II). However, in every study the increased RBF and decreased EpAH (accompanying the saline 100 load) returned to or toward the preloading control values as the natriuresis subsided. These re- FIG. 4. THE EFFECTS OF AORTIC CONSTRICTION ON RBF sults are summarized in Table II, and consecutive AND EPAH DURING MAINTAINED SALINE LOAD. Points collection periods from a representative experi- shown are the means of three or more consecutive and uniform collections from the left kidney. Values for EPAH ment are shown in Figure 2. were reduced below inital controls during saline loading In five experiments GFR and filtered sodium (open circles). During aortic constriction these reduced were unchanged or decreased during saline load- values increased (solid circles) as RBF decreased. 934 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER

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- or-eq di 00 o O U>_WO-0M t4 ri Vat- f- co0 -1 . 4 1 1 18 .0) .t-01) - t 4 20O44 .e -- eq d-0000 H o 00 o r_ )__ ,._d eq eq eq 936 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER duced during saline loading by constriction of the nal plasma flow was reduced proportionately aorta between the renal arteries. In each experi- more than CPAH, but with increased aortic con- ment EPAH (which was reduced during saline load- striction EPAH did not continue to increase striking) was increased as total blood flow decreased ingly as RBF decreased. (Figure 4). However, EPAH was usually not in- In 5 of these 16 experiments the relationships creased to the higher values present before saline between filtered and excreted sodium necessary loading, even when total renal blood flow was re- to demonstrate changes in tubular reabsorption duced to values equal to or less than the presaline were not achieved during aortic constriction. In loading control rates (second constriction, experi- the remaining 11 experiments changes in the net ment 15, Table IV). During mild aortic con- tubular reabsorption of sodium were demonstrated. striction the calculated noncortical fraction of re- The association between these changes in tubular reabsorption and changes in noncortical plasma flow is summarized in Figure 5. Details of three representative experiments are given in Table IV. In seven experiments mild aortic constriction (aortic pressure, 70 to 85 mm Hg) was employed during saline loading, and measurements of hemodynamics and sodium excretion were compared to those present during the stable natriuresis immediately preceding the reduction of blood flow. In six of these experiments the reduction in sodium excretion was not accompanied by an equivalent reduction in filtered sodium. Therefore, in these six studies increased net tubular reabsorption of sodium occurred in the presence of mild aortic constriction during saline loading. This increased reabsorption of sodium was associated with increased EPAH and decreased noncortical plasma flow (first constriction, experiment 13, Table IV; left side of Figure 5). GFR, CPAH, and sodium excretion in the contralateral kidneys were unchanged during the periods of inter-renal aortic constriction. In eight experiments additional aortic constriction (aortic pressure, 40 to 60 mm Hg) dur- FIG. 5. CHANGES IN THE NET TUBULAR REABSORPTION ing saline loading reduced filtered sodium to rates OF SODIUM DEMONSTRATED BY AORTIC CONSTRICTION DUR- clearly below the presaline loading control values ING SALINE LOADING. Values are the means of three or at a time when excreted sodium was to or more consecutive collections from the left kidney. Shown equal on the left are demonstrations of increased tubular reab- greater than the preloading values. Thus, in these sorption of sodium during mild aortic constriction dur- eight experiments it was demonstrated that net ing the maintained saline load. Sodium excretion de- tubular reabsorption of sodium was decreased be- creased without an equivalent decrease in filtered so- low that present before saline loading. In all eight dium as noncortical plasma flow (see text) decreased. of these experiments (during increased aortic Changes on the left are from mean values during the saline load and before aortic constriction. Shown on the constriction) EPAH remained lower than the pre- right are demonstrations of decreased tubular reabsorp- saline loading control values, and noncortical tion during saline loading demonstrated by more marked plasma flow remained greater than control in all aortic constriction. These changes in filtered and ex- but one experiment. In this single experiment creted sodium and noncortical plasma flow are from (last experiment, right side of Figure 5) sodium mean values before saline loading. In all but one experiment in which excreted sodium was increased in the excretion was reduced to rates only slightly dif- presence of reduced filtered sodium, noncortical plasma ferent from the preloading control, and although flow was increased (see text). noncortical plasma flow did not remain increased, RENAL HEMODYNAMICS DURING SALINE LOADING 937

EPAH remained less than control (.773 compared TABLE V to .814). These results are summarized in the Simultaneous measurements of extraction ratio and renal right-hand portion of Figure 5, and details of three blood flow using PAH and I'll Diodrast or Hippuran* experiments are given in Table IV (second con- Extraction striction, experiments 13 and 14, and experiment ratio Eils1 RPF RPF (I131) 15). PAH 113 EPAH PAH 1131 RPF (PAH) mi/min Control observations. To establish that the Control 0.620 0.628t 1.01 100 lOOt 1.00 changing extractions of PAH were not related to Saline loading 0.291 0.319 1.09 186 195 1.05 some unrecognized systematic error in the meas- Control 0.765 0.805t 1.05 180 174t 0.97 urement of PAH, extraction ratios of PAH and Saline loading 0.677 0.741 1.09 429 404 0.94 I131 I131 Control 0.825 0.777t 0.94 113 106t 0.94 Diodrast or Hippuran were measured si- Saline loading 0.786 0.747 0.95 165 159 0.96 multaneously in five experiments. These results Postload 0.840 0.777 0.93 125 120 0.96 are summarized in Table V. Both the extraction Control 0.826 0.726T 0.88 177 164T 0.93 Saline loading 0.669 0.627 0.94 368 368 1.00 and clearance of Hippuran 1131 were 5 to 12% Postload 0.830 0.732 0.88 188 178 0.95 less than simultaneous determinations of PAH. Control 0.810 0.735t 0.91 109 § However, the changes in extraction and clearance Saline loading 0.741 0.657 0.89 224 Postload 0.805 0.714 0.89 180 during saline loading were parallel for the two substances. EDiodrast was 1 to 9%o greater than * Each value is the mean of three or four consecutive collection periods from the left kidney only. Additional abbreviation: RPF simultaneously measured EPAH, but parallel changes = total renal plasma flow. t Diodrast-I'3. in the extraction of these two substances also oc- Hippuran-1131. curred during saline loading. § Radioactivity in urine samples not measured. Even though arterial concentrations of PAH stance, in the absence of significant chemical con- in the present studies (0.5 to 2.5 mg per 100 ml) centrations, should eliminate the influence on the were well below expected Tm values, the possi- extraction ratio of even large changes in transport bility was considered that during saline loading the maxima. In two experiments the extraction of tubular transport maximum for PAH was ap- tracer amounts of Diodrast-I31 was measured proached or exceeded, thereby resulting in the without the simultaneous infusion of PAH (first observed decreased extraction ratios. This pos- experiment, Table II, and first two experiments, sibility was examined in three different ways: 1) Figure 1). EDiodrastI was decreased during sa- TmPAH was determined before and during saline line loading in exactly the same manner as was loading in two experiments under precisely the chemically measured PAH in all other experi- same conditions as in all other experiments. Be- ments. fore saline loading these values averaged 4.6 and Another possibility considered was that during 7.5 mg per minute (left kidney only), and during saline loading, increases in capillary and inter- saline loading the respective values were 5.3 and stitial volume (and perhaps other unrecognized 6.4 mg per minute. These values of TmpA are factors) may impose a diffusion barrier that well above the tubular load of PAH (usually less limits the access of PAH to the cellular sites of than 1.5 mg per minute per kidney) employed in transport. If the extraction of PAH (from renal the present studies. 2) If the decreased extraction cortical blood) is near 100%o before saline load- ratios during saline loading were due to an ap- ing, but becomes limited by diffusion during sa- proach toward the transport maxima, then an in- line loading, then a larger (more slowly diffusing) crease in the tubular load of PAH during saline transported molecule should be affected to a loading should result in a further decrease in greater extent than PAH. However, this was not EpAH. In two experiments the rate of infusion the case in the two experiments in which the ex- of PAH was changed approximately twofold, both tractions of Diodrast (mol wt, 510) and PAH before and after saline loading. EPAH decreased (mol wt, 194) were measured simultaneously. during saline loading, but at these low rates of in- The ratio of EDiodrast/EpAH was not decreased fusion of PAH no relationship between tubular during saline loading (Table V). Furthermore, load and EPAH was observed, either before or EPAH remained depressed during saline loading during the saline load. 3) The measurement of despite reductions of blood flow to values less than isotopic tracer amounts of the transported sub- control (experiment 15, Table IV). This latter 938 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER observation makes it unlikely that increased blood the presence of decreased tubular reabsorption of flow per se limits the extraction of PAH. sodium (as compared to presaline loading values) Discussion also demonstrated an inverse relationship between tubular reabsorption and renal blood flow. How- The present studies provide further demonstra- ever, the latter observations do not eliminate the tions of the dissociation that may occur spontane- possibility that the diminished tubular reabsorption and the ously between the filtered load of sodium of sodium resulted from extrarenal factors initiated saline loading in rate of sodium excretion during by saline loading, and that the observed hemody- seven experiments the the dog (1, 2). In four of namic changes are incidental and not related fall in sodium excretion after discontinuing the reabsorption of sodium. infusion of saline clearly exceeded the fall in causally to the diminished The factors' determining the renal extraction filtered sodium. In five experiments of the se- PAH are not entirely understood. It ries, no increase in GFR and filtered sodium oc- ratio for curred during saline loading, despite large in- has been suggested that blood leaving juxtamedul- the vasa recta creases in sodium excretion. Thus changes in the lary glomeruli and passing into net tubular reabsorption of sodium during saline does not perfuse sufficient cortical convolutions to loading were evident spontaneously in nine of the allow complete extraction of Diodrast, PAH, and present experiments. Also, the present studies other derivatives of hippuric acid, and that this employing aortic constriction provide additional factor accounts in part for the failure of the kidney demonstrations of decreased tubular reabsorption to completely extract these substances (13-16). of sodium during saline loading, by means of con- The anatomy of the medullary circulation is controlled reductions in the filtered load of sodium sistent with this premise (17). However, Thurau (1, 3-6). The changes in tubular reabsorption has reported that during antidiuresis the concen- of sodium observed both spontaneously and during tration of PAH in blood collected from vasa recta aortic constriction were accompanied by consistent by micropuncture may be 4 to 12 times as great as changes in EPAH and renal blood flow. Decreases the concentration of PAH in arterial blood (18). in tubular reabsorption of sodium were associated Since the concentration of PAH in vasa recta with decreases in EpAH and, in all but one instance, blood was not found to be low (as expected in re- increases in noncortical plasma flow. Conversely, nal venous blood), these latter findings are not increases in sodium reabsorption were accompanied inconsistent with the possibility that PAH is not by increased EpAH and decreased noncortical removed from blood perfusing the renal medulla. plasma flow. Although increases in total renal Such observations (18) could be explained by a blood flow were present during most observations "leak" of PAH from collecting duct or Henle's of decreased tubular reabsorption of sodium, this loop into vasa recta. However, it would not appear was not true in all experiments. In some studies that such a leak of PAH from tubular lumen into decreased tubular reabsorption of sodium accom- capillary could explain the present changes in panied by decreased EPAH and increased non- EPAH, since EPAH decreased during diuresis at a cortical plasma flow was observed in the presence time when tubular fluid concentrations would be of reduced CPAH and total renal blood flow. lower and net loss into blood should be less. Mild unilateral reductions in renal perfusion That the extraction of PAH and similarly trans- pressure during saline loading resulted in increased ported organic compounds may represent in part EPAH and reduced renal blood flow accompanied the distribution of blood between the renal cortex by immediate large decreases in sodium excretion and medulla remains a distinct possibility. Some without equivalent decreases in filtered sodium. support for this concept is afforded by the present Sodium excretion and reabsorption were unaf- observations. Thurau and Deetjen have suggested fected in contralateral control kidneys. These ob- that renal medullary blood flow is not autoregu- servations provide strong evidence that diminu- lated and therefore is affected more readily than tion in renal blood flow may result in increased cortical blood flow by changes in perfusion pres- net tubular reabsorption of sodium through intra- sure (19). Such a relationship between perfu- renal mechanisms. During more marked aortic sion pressure and medullary blood flow could ac- constriction the maintained decreases in EPAH and count for the increases in EPAH observed during continued increases in noncortical plasma flow in aortic constriction in the present studies. Re- RENAL HEMODYNAMICS DURING SALINE LOADING 939 duced perfusion pressure would produce a rela- The mechanisms whereby increases in renal tively greater decrease in medullary blood flow blood flow, and more specifically increases in non- than in cortical blood flow. If PAH is not ex- cortical plasma flow, may decrease the net tubular tracted from blood perfusing the medulla (ex- reabsorption of sodium are only speculative. If, cept to the extent of filtration through juxtamedul- as suggested above, renal plasma flow from which lary glomeruli), then the maintenance of cortical PAH is not extracted represents in part medul- blood flow as medullary flow decreased would lary blood flow, then the present studies provide result in a rise in EPAH as was observed in the evidence that net reabsorption of sodium may present experiments. change inversely with changes in medullary blood No evidence could be obtained in the present flow. This interpretation of the present data sup- study that the ability to transport PAH was di- ports the earlier suggestion that increases in minished during saline loading. This is in con- medullary blood flow during saline loading may trast to the report of Levy and Ankeney that diminish sodium reabsorption. In a previous re- TmpAH decreased during hypertonic saline load- port from this laboratory (6) it was suggested ing (20). On the other hand, Mudge and Taggart that an increased medullary blood flow during (21) found no decrease in TmpA in dogs infused saline loading may result in decreased medullary with isotonic saline in amounts sufficient to in- hypertonicity, a decreased passive reabsorption crease urine flow and GFR. Also, it did not ap- of water from the descending limb of Henle's pear likely in the present studies that diffusion loop, and consequently the delivery of a larger from blood to the cellular transport sites was a volume of tubular fluid with a lower sodium con- limiting factor in determining EPAH during saline centration to the ascending limb of Henle's loop. loading. The possibility that the changes in ex- This increased rate of flow of more dilute fluid traction of PAH, Diodrast, and Hippuran were past the transport sites of the ascending limb could in some way related to the changes in the rate of then result in a decreased net reabsorption of so- urine flow that accompanied saline loading cannot dium at these sites. In addition, this premise re- be excluded, but seems unlikely. As discussed quires, 1) that the rate of transport by the as- above, any leak of PAH from tubular lumen back cending limb is not influenced to a great extent by into blood should be greater at low urine flows the transtubular gradient of sodium concentration, than at high urine flow when the tubular fluid but transport at this site does relate in some di- concentration of PAH is lower. It is possible, rect fashion to the absolute concentration of sodium however, that the permeability of the tubule to in the tubular fluid, and 2) that increases in medul- these substances is greater during saline loading, lary blood flow decrease medullary interstitial hy- and the loss from tubule to blood thereby in- pertonicity and passive water reabsorption from creased. It has been suggested that EpAH less the descending limb of Henle's loop. The first of than 100%o may be due to the perfusion of renal these requirements should obtain if the back leak capsule, hilar adipose tissue, and other "non- of sodium into the ascending limb is negligible, functioning" renal structures (17). Although the and if some diffusion barrier separates the luminal entry of such blood into the renal vein may ac- sodium from the active transport site. The sec- count in part for extraction ratios less than 100%o, ond requirement would appear to be on sound theo- it appears unlikely that such blood flow could ac- retical grounds (22-24). The large increases in count for the striking decreases in EPAH observed sodium excretion observed in the present studies in the present studies. This noncortical plasma (as great as 14% of the filtered load, in the ab- flow averaged 32 ml per minute per kidney before sence of increased GFR) render it likely that the saline loading and increased to 116 ml per minute reabsorption of sodium may be diminished in per kidney during saline loading. It is suggested, other portions of the nephron during saline load- therefore, that the decreased EPAH during saline ing. If proximal reabsorption is diminished dur- loading may reflect in part a relative increase in ing saline loading, an increased medullary blood medullary blood flow. Since total renal blood flow flow could contribute to increased sodium excre- increased during saline loading in every experi- tion (through the above mechanism) by limiting ment, the decreased EPAH also could represent reabsorption by the loops of the increased delivery an absolute increase in medullary blood flow. of sodium from the proximal convolution. 940 LAURENCE E. EARLEY AND ROBERT M. FRIEDLER Alternatively, the decreases in EPAH occurring Summary during saline loading may represent a relative in- The effects of isotonic expansion of the extra- crease in both medullary blood flow and juxta- cellular volume on filtered and excreted sodium, medullary glomerular filtration. If the reabsorp- renal blood flow, and extraction ratios of p-amino- tive capacity for sodium of juxtamedullary neph- hippurate (PAH), Diodrast, and Hippuran were rons is exceeded during such a redistribution of studied in anesthetized dogs. During saline load- filtrate, changes in net reabsorption of the total ing renal blood flow increased and the extraction filtered load of sodium could occur without an ratio of PAH (EpAH) decreased. In some ex- actual diminution of tubular reabsorptive capacity. periments spontaneous changes in the net tubular This appears somewhat unlikely, since in some of reabsorption of sodium were observed during the the present studies saline loading resulted in no course of saline loading. Changes in net tubular change in GFR, which would require that the in- reabsorption of sodium during the natriuresis of creased filtration by some glomeruli was exactly saline loading could be demonstrated also by uni- balanced by a decreased filtration through other lateral reduction of renal blood flow. Decreased glomeruli. In addition, the possibility cannot be reabsorption of sodium was always accompanied excluded that increases in renal blood flow (or an by decreased EPAH and increased renal blood flow, intrarenal redistribution of blood as suggested by whereas increased reabsorption was accompanied the present observations) may affect tubular reab- by increased EPAH and decreased blood flow. sorption of sodium through other unidentified in- The fall in EPAII during saline loading did not trarenal mechanisms. appear to be due to diminished ability to transport These results do not provide evidence to sug- the substance, and it is suggested that the changes gest the mechanism whereby such a change in the in the extraction ratio may relate in part to changes intrarenal distribution of blood may occur during in noncortical plasma flow, which could include saline loading. Arterial pressure usually was not medullary blood flow. A causal relationship may increased during saline loading, and this is con- exist between these hemodynamic changes and the sistent with previous reports that saline loading in associated changes in sodium reabsorption. These the dog may not increase arterial blood pressure observations are consistent with the suggestion (25). However, the large increases in renal that diminished net tubular reabsorption of so- blood flow that occur (in the absence of increased dium during saline loading may relate in part to perfusion pressure) would require that the re- an increased medullary blood flow. sistance to blood flow through the kidney be strikingly diminished during saline loading. In the Acknowledgments present experiments the arterial hematocrit was The authors are indebted to Deborah Lufkin, Susan Howard, and Barbel Juergens for their assistance with reduced to a mean value of 27 (control mean, 40), portions of these studies. and this could be a factor that both decreases the resistance to blood flow (26) and affects the dis- Addendum tribution of blood within the kidney (27). Acute Dirks, Cirksena, and Berliner have recently reported reductions in the hematocrit are known to be as- that isotonic saline loading in the dog is associated with sociated with reductions in (26-28), but large decreases in fractional reabsorption in the proxi- EPAH mal convolution, and that these changes persist in the such studies have not provided information on presence of reduced glomerular filtration (31). If such filtered and excreted sodium. Also, expansion of changes in proximal reabsorption by cortical nephrons the plasma volume with albumin may decrease accessible to micropuncture are representative of the EPAH 29, 30), and Elpers and Selkurt (16) total nephron population, then it is unnecessary to postu- (16, late that saline loading diminishes the reabsorption of have suggested that this may represent an in- sodium in more distal portions of the nephron as dis- crease in medullary blood flow. These latter au- cussed in the text of this report. In view of the findings thors reported a mean decrease in excreted sodium of these latter authors and the present observations, more as EPAH decreased during albumin infusion; how- emphasis should be given to the possibility that proximal tubular reabsorption of sodium may be regulated in part ever, these latter observations were made during by some indirect intrarenal mechanism and that a change saline infusion, and individual details of GFR and in blood flow is a factor affecting such a regulatory sodium excretion were not reported. system. RENAL HEMODYNAMICS DURING SALINE LOADING 941 References 17. Smith, H. W. The Kidney: Structure and Function in Health and Disease. New York, Oxford Uni- 1. De Wardener, H. E., I. H. Mills, W. F. Clapham, versity Press, 1951. and C. J. Hayter. Studies on the efferent mecha- K. Amer. Med. of the sodium diuresis which follows the ad- 18. Thurau, Renal hemodynamics. J. nism 1964, 36, 698. ministration of intravenous saline in the dog. Clin. Sci. 1961, 21, 249. 19. Thurau, K., and P. Deetjen. Die diuresc bei arteri- 2. Earley, L. E. Effects of renal arterial infusion of ellen Druksteigerungen. Bedentung der Hamo- albumin on saline diuresis in the dog. Proc. Soc. dynamik des Niereumarkes fur die Harnkouzen- exp. Biol. (N. Y.) 1964, 116, 262. trierung. Pfluigers Arch. ges. Physiol. 1962, 274, 3. Levinsky, N. G., and R. C. Lalone. The mechanism 567. of sodium diuresis after saline infusion in the 20. Levy, M. N., and J. L. Ankeney. Influence of glo- dog. J. clin. Invest. 1963, 42, 1261. merular filtration rate upon the renal tubular reab- 4. Blythe, W. B., and L. G. Welt. Dissociation between sorption of sodium. Proc. Soc. exp. Biol. (N. Y.) filtered load of sodium and its rate of excretion in 1952, 79, 491. the urine. J. clin. Invest. 1963, 42, 1491. 21. Mudge, G. H., and J. V. Taggart. Effect of acetate 5. Rector, F. C., Jr., G. Van Giesen, F. Kiil, and D. W. on the renal excretion of p-aminohippurate in the Seldin. Influence of expansion of extracellular dog. Amer. J. Physiol. 1950, 161, 191. volume on tubular reabsorption of sodium inde- 22. Gottschalk, C. W., and M. Mylle. Micropuncture pendent of changes in glomerular filtration rate study of the mammalian urinary concentration and aldosterone activity. J. clin. Invest. 1964, 43, mechanism: evidence for the countercurrent hy- 341. pothesis. Amer. J. Physiol. 1959, 196, 927. 6 Earley, L. E., and R. M. Friedler. Observations on 23. Hargitay, D., and W. Kuhn. Das Multiplikatron- the mechanism of decreased tubular reabsorption sprinzip als Grundlage der Harnkonzentrierung in of sodium and water during saline loading. J. clin. der Niere. Z. Elektrochem. 1951, 55, 539. Invest. 1964, 43, 1928. 24. Berliner, R. W., N. G. Levinsky, D. G. Davidson, and 7. Kennedy, T. J., Jr., J. G. Hilton, and R. W. Berliner. M. Eden. Dilution and concentration of the urine Comparison of inulin and creatinine clearance in and the action of antidiuretic hormone. Amer. J. the normal dog. Amer. J. Physiol. 1952, 171, 164. Med. 1958, 24, 730. 8. Harvey, R. B., and A. J. Brothers. Renal extraction 25. Barger, A. C., F. E. Yates, and A. M. Rudolph. Re- of para-aminohippurate and creatinine measured nal hemodynamics and sodium excretion in dogs by continuous in vivo sampling of arterial and re- with graded valvular damage, and in congestive nal-vein blood. Ann. N. Y. Acad. Sci. 1962, 102,46. failure. Amer. J. Physiol. 1961, 200, 601. 9. Walser, M., D. G. Davidson, and J. Orloff. The 26. Johnson, B. L., Jr., and J. F. Murray. Renal func- renal clearance of alkali-stable inulin. J. clin. In- tion during acute normovolemic and hypervolemic vest. 1955, 34, 1520. anemia. Clin. Res. 1963, 11, 243. 10. Smith, H. W., N. Finkelstein, L. Aliminosa, B. 27. Kinter, W. B., and J. R. Pappenheimer. Renal ex- Crawford, and M. Graber. The renal clearance traction of PAH and of Diodrast-131 as a function of substituted hippuric acid derivatives and other of arterial red cell concentration. Amer. J. Phys- aromatic acids in dog and man. J. clin. Invest. iol. 1956, 185, 391. 1945, 24, 388. 28. Thompson, D. D., F. Kavaler, R. Lozano, and R. F. 11. Wolf, A. V. Total renal blood flow at any urine flow Evaluation of the cell or extraction J. Phys- Pitts. separation hypothe- fraction (abstract). Amer. sis of autoregulation of renal blood flow and fil- iol. 1941, 133, 496. Blood filtration rate-and PAH R. P. P. B. Hamilton, K. tration rate. flow, 12. Phillips, A., V. Dole, extraction as functions of arterial pressure in nor- Emerson, Jr., R. M. Archibald, and D. D. Van mal and anemic dogs. Amer. J. Physiol. 1957, 191, Slyke. Effects of acute hemorrhagic and traumatic 493. shock on renal function of dogs. Amer. J. Physiol. 1946, 145, 314. 29. Cargill, W. H. Effect of intravenous administration 13. Reubi, F. C. Objections 'a la theorie de la separation of human serum albumin on renal function. Proc. intrarenal des hematies et du plasma. Helv. med. Soc. exp. Biol. (N. Y.) 1948, 68, 189. Acta 1958, 25, 516. 30. Michie, A. J., N. Gimble, C. Riegel, and M. Ragni. 14. Pitts, R. F. Physiology of the Kidney and Body Opening of intrarenal arteriovenous shunts with- Fluids. Chicago, Year Book, 1963. out cortical ischemia by sudden administration of 15. Slotkoff, L. M., G. M. Eisner, and L. S. Lilienfield. salt-poor concentrated human serum albumin. J. PAH extraction ratio, an index of renal medullary appl. Physiol. 1951, 3, 472. blood flow? (abstract). Clin. Res. 1964, 12, 259. 31. Dirks, J. H., W. J. Cirksena, and R. W. Berliner. 16. Elpers, M. J., and E. E. Selkurt. Effects of albumin The effect of saline loading on sodium reabsorp- infusion on renal function in the dog. Amer. J. tion by the proximal tubule of the dog. Fed. Physiol. 1963, 205, 153. Proc. 1965, 24, 520.