The Nature of the Action of Intravenous Aldosterone: Evidence for a Role of the Hormone in Urinary Dilution

THE NATURE OF THE ACTION OF INTRAVENOUS ALDOSTERONE: EVIDENCE FOR A ROLE OF THE HORMONE IN URINARY DILUTION

Edmund H. Sonnenblick, … , Paul J. Cannon, John H. Laragh

J Clin Invest. 1961;40(6):903-913. https://doi.org/10.1172/JCI104329.

Research Article

Find the latest version: https://jci.me/104329/pdf THE NATURE OF THE ACTION OF INTRAVENOUS ALDOSTERONE: EVIDENCE FOR A ROLE OF THE HORMONE IN URINARY DILUTION* By EDMUND H. SONNENBLICK,t PAUL J. CANNON AND JOHN H. LARAGH (Fromi the Deparbiwitt of Medicine, College of Physicians and Surgeons, Columbia Unzivcrsitv, and the Presbyterian Hospital, New York, N. Y.)

(Submitted for publication September 15, 1960; accepted January 13, 1961) Aldosterone increases the renal retention of so- This action takes place in the tubule at a locus dium chloride and promotes the excretion of po- distal to that of isosmotic reabsorption. Also, this tassium ions ( 1-11 ); but where and how the hor- effect of the hormone on sodium chloride reab- mone acts in the renal tubule is poorly understood. sorption appears to be dissociated from the effect The present study was designed to characterize on potassium excretion. further the mode and site of action of aldosterone in the nephron. EXPERIMENTAL Information can be obtained about the site of action of a compound by observing its effect on Seven studies were performed on 3 subj ects without evidence of renal or cardiovascular disease. Four of the free water formation (12). According to a cur- experiments were done with subj ects maintained on a rent concept of renal physiology (13), reabsorp- normal NaCl intake (4 to 6 g NaCl per day for 7 tion of solute (sodium chloride) is isosmotic in days), two with the subj ects on a higher intake of the proximal tubule (14), whereas, in the more salt for 7 days (8 to 20 g NaCl per day), and one after distal reabsorption may or may not be drastic salt deprivation (less than 250 mg per day for segments, 6 days). In two subjects on normal salt intake, con- isosmotic (15, 16). During water diuresis (ab- trol studies of similar protocol but without administra- sence of antidiuretic hormone) the distal reab- tion of aldosterone were performed. All experiments sorption of solute is selective, i.e., occurs without were conducted in the fasting state at the same early isosmotic amounts of water, leaving "solute-free" morning hour with the subjects in a recumbent position. Thus, by de- Water diuresis was induced by having the patient in- water behind for excretion (17). gest about 1,500 ml of water by mouth during the hour termining the effect of a compound on solute ex- before the experiment and was subsequently maintained cretion and on free water formation during main- by intravenous infusion of 5 per cent dextrose and water tained water diuresis, information may be ob- at a constant rate, at least 2 ml per minute greater than tained about its site of action (12). If aldosterone urinary output. Adequate control periods were obtained were to act to promote isosmotic reabsorption of until a steady state of maximum urine flow was demon- strated, so that any subsequent change in free water sodium, the consequent reduction in solute excre- clearance could not be attributed to an increasing water tion would be accompanied by a fall in urine flow diuresis. and no change or fall in free water excretion. When a steady state of maximum water diuresis had However, if aldosterone acts only at a more distal been achieved, 1 mg of d,l-aldosterone monoacetate in where is the reduced 10 ml of 10 per cent ethanol was administered intrave- site, reabsorption selective, nously.' This was followed by another 1 mg given in sodium excretion would be accompanied by no the dextrose and water infusion over the next hour. change in urine flow and hence, by a rise in free After the aldosterone administration was complete, the in- water excretion. fusion of dextrose and water was continued at a con- In the present study it has been shown that stant rate. of Blood samples were taken via an indwelling hepari- aldosterone can promote abstraction sodium nized needle and urine collections were made with an in- chloride exclusive of water from the tubular urine. dwelling catheter except in Subjects S.H. and M.U., young males in whom adequate voluntary bladder empty- * This work was supported by the 'United States Public ing was possible at high rates of urine flow. Health Service (Grant H-1275) and by Mrs. R. C. duPont. I d,l-Aldosterone monoacetate, 1,000 ltg equivalent to t Present address: National Heart Institute, Bethesda, 500 pig active d-aldosterone supplied by Ciba Pharma- Md. ceutical Products, Summit, N. J. 903 904 EDMUND H. SONNENBLICK, PAUL J. CANNON AND JOHN H. LARAGH

I 00 V~ U) ' 0% a, C\ 0% 0% el; 00 t. t- N Cd E (0 et a) -4 :L 00 - 00 00 N0 0. V 0% Cl 00 00 0 0 Cl4 CN Cl4 E d 0 U) 0 U) 4- V 00 t U) U0 U) Cl30 U) U) U) U) U) ._ U) U)\- 0t 0) at U) m4 0- U-) 0)00 Cl- 00 00 Nb 0 o o0 tor U) 0) * 0 o4 of *0.i q1) 0) 0 00 UI) t- t- Cl %0 111 d i. z 0-%U) 0 0) r-0-o -o V '0 0 %00 0w -o 4-

U) 0 6 *2- Nb Cl U) -j4 t- Cl 0) ?8t 0 en U) > t-U); LI; 0 "0 - ho 4- m co ¢.1 w U) V Vt \0 U) -4 0. 10 a o 0 m oo V - 0 0 0 0 00 z .2 4-i V U) 0 0. u 0 00 V -- 0 '0 0 OOC) ud C 00M N *-0) o ovou 0) o 0) U1) -et ._ ._ 0 - U) V 0 U) V -6 0 (3 *.0 01) 0 0. ¢ 0. 0)00 Cl 0V .- to U) S 0% C 0 - CCl 01) 0 0. .0 blo 0 - _U U)1 o U) Ul) 0 0) I-. 0 o6o6 Y %0OV Vo o6 o o6 o6 o6 c~ 01) Cn .5 0i r.z 04- "0 0) a 0% . 00.. V V 0 U) V 0 V 0 u 10 0--ClC 0 0. 00 o- as a M '" 00U)'00+V 0%4 0 -I U) t- -0 U -4 000 0u 0 0- _oo 0) 0. 0 U) L4 00 000~nS UE 0 0UV 0) b* 4-0 00- x U) U) 0'm-CC\0-0C (L 120, to +++++++. r- 0 )-- -0C z CN -Cl 0- - 0 0 U,)VnU) U)~ Cl Vo 00k- U) (n N Cl U U) o4otoUV Cl00 -4 U-) 4/) 0 00000 0 0 0 0 44 Cl CN Cl 0- Cl 0- t- - 000 - +++C++00- - 0-Cl 0) 00 Cl t ItUl I+ +++++++ ALDOSTERONE AND URINARY DILUTION 905

Plasma and urine samples were analyzed for inulin or creatinine, para-aminohippuric acid, and sodium, potassium and chloride, by methods previously described -1'0 "20to (0)'14 O m '-.0 0 2 - "t (12). The urinary pH was measured by a Beckman pH 1r "1 rz -4-- eqaN m -)en meter on freshly voided samples and the urine and 'i 0 plasma urea concentrations were determined by a modi- -0 fication of the urease method of Van Slyke and Cullen (18). The urine and plasma total solute concentration le01 -l Nt % m ,4 C,4 ° ON 000 -t was measured with a Fiske osmometer. 0 l 4 L Calculations. As indicated by Smith (13) and by . 61 ci_ lici4 i4 ci- 4-J .0>W Anslow urine can be divided into two o.oo 00N 00 Uto 0oNo00- Wesson and (17), t t f;4...... - - N II 1 _" tn K _ moieties: the osmolar clearance (C0,,), the volume of 7 -- _q-. V l M M ' 't d1. m ; water necessary to contain the urinary solutes in a solu- tion isosmotic with the plasma (Cosm = UVosm/Posm); 0) water net excess or a IC (1 (Ds o Xo 10 mUo00 ON CWo-C) -I and the free clearance (CH20), the - 3 rto U SC-14 00(0) m U.)"1t deficit of water beyond the osmolar clearance. During C) water water is a positive value diuresis the free clearance 0> and is calculated as CE220 = V - Uo.mV/Posm, where V 00 0 0o -0 -oC r 0000 t-00 *) "I 0N K 00 I- 00r- 011) is the urine flow in milliliters per minute and Uo.m and 00 eo 1.u0 02 Posm are the solute concentrations of urine and of plasma 4-)a in milliosmoles per kilogram of water. OU) 00 Co CD 00(0 u) oo m -t -! 0e Il 6 \0 \ RESULTS Q The results of these experiments are summa- _Cd 00 - t 4-. rized in Tables I, II and III and in Figures 1 > *o in (en% 00 00 U00 '- el; Cl) F r- r- en oo00 00 to , -c c to_4r 4 t through 4. In Table III, a typical control proto- 0b - 0)En ( col is given. In Table I the complete protocol of 0) com- one experiment is given, and in Figure 1 the .0 *o > ttU) Onme0 °C ~t I-.. X- U-) 0 'IO00 00 -~ t- %0 .. >o._ Subject M.U.- Normal Diet *0); w Img d.l. aldosterone L.V. + 0 XU = lmg in 5% D/W infusion r0 in E oe d I-- tJ4%0 M %0ut I- I T--- I -- I - !-- U) U) -. _ U- -- X4 100 0) : 0o 0i 80 (00) UVNG* 60 en 0s It 0 40 Cm LOm XOr- Q o C mm 0 U m 0 20 _I < ¢ n0. 0) 0 oBS. 60 0 u u 04) 40 +4U) \00 m - 0 20L I4t0 0 0 CSM Ci 502 - -4C. c" "cI q N 00 ." 4 - UVK+ 30 - _ _ C C)U U _ Cd 04) 700 oQ 500 Uvosm - ._. *josm/min.300 o o o o o o- -0 o-J-0 + 2 0 Z a Cosm ._ or o= -0=-.0 0-04 = -a o -a ml / min. 0 0¢ O¢0¢ W¢ ¢ O¢ O¢ 14- 0W

v 152 -- 4-e ml/min. 13 as , ct . ) *_Cv 0 --e, -100 0 100 200 300 400 500 600 EL. U-o

o 00 . Minutes >._o >. t. :. 0 Fi GRAPH OF THE RESULTS OF A REPRESENTATIVE FIG. 1. 4 0 - 0- CLEARANCE STUDY (SEE TEXT). -; 906 EDMUND H. SONNENBLICK, PAUL J. CANNON AND JOHN H. LARAGH

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-60C ;Ne +100 D- K+ K K -,Pel -8001NXI I I I X--E I.IX I I I I -100 N.+ cl- II -100 J.0. KU. -2000

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:k -500 4

-600 +100- Ki- .1,ff AAA

80V II 1I-F I I -100 -W 100 200 300 400 500 600 100 20O 300 400 500 600 Minutes I Minutes FIG. 2. EFFECT OF ALDOSTERONE ON SODIUM, POTASSIUM AND CHLORIDE EXCRETION PLOTTED AGAINST TIME IN FOUR DIFFERENT STUDIES. On the ordinates the net changes from the control values are plotted for each collection period. The increased potassium excretion is often out of phase with the reduction in sodium chloride excretion. Also the increase in potassium excretion is of considerably lesser magnitude than the reduction in sodium chloride excretion (see text). plete results of another experiment are depicted renal hemodynamics and therefore appeared to be graphically. due to the action of aldosterone on the renal tu- Effect on renal hemodynamics. Aldosterone bules. administration produced no significant changes Effect on sodium and chloride excretion. Fol- in either glomerular filtration rate or renal plasma lowing aldosterone administration there was a de- flow (Tables I and II). The subjects varied con- lay of from 20 to 60 minutes before a significant siderably in their control glomerular filtration rate reduction in sodium chloride excretion developed. values from 102 ml per minute in M.U. to 213 ml During the first 20 to 60 minutes of aldosterone per minute in J.O.; a similar variation was noted administration variable effects were observed, and in the renal plasma flow. Because no consistent in two of the seven studies a transient increase in alteration was observed in a given patient in these sodium chloride excretion actually occurred in this values after injection of the hormone, the marked early period (Figure 2, Tables I and II). Then, changes in solute and electrolyte excretion Ito be sodium chloride excretion was sharply reduced. described were not attributable to alterations in The reduction reached a maximum 2 to 4 hours ALDOSTERONE AND URINARY DILUTION 907 after the aldosterone administration was begun. was maintained for about 6 hours in two recum- The depressed sodium chloride excretion did not bent normal subjects. No significant changes in return toward the control values until 6 to 8 hours sodium, potassium or chloride excretion were ob- after completion of aldosterone administration. served during this period. In Subject O.G., The magnitude of the sodium retention (i.e., whose protocol is presented in Table III, a stable / UNaV from the control level) was the greatest water diuresis was established. Osmolar clear- in Subject J.O., who had the highest filtered load ance fell slightly in the first 2 hours with stabili- of sodium, and was least in Subject M.U. when zation at 2.7 ml per minute while urine volume he was sodium-depleted. Presumably, in this and free water clearance (CH2O) remained rela- latter instance a maximal endogenous aldosterone tively unchanged. In a second normal subject, effect was present (19, 20), and no further re- E.S., a similar course of results prevailed with an duction in the UNaV could be produced by aldo- average urine flow of 17.6 ml per minute in the sterone administration. In the other six studies first 190 minutes and 16.0 ml per minute in the the rate of sodium excretion was reduced by from ensuing 160 minutes. Osmolar clearance fell 40 to 86.5 per cent of the control values, and the slightly from an average of 2.8 to 2.5 ml per min- absolute rate of excretion was reduced by from ute during the same periods with a concomitant 59 to 441 uEq per minute in these six studies. decline of free water clearance from 14.8 to 13.5 A parallel but, in general, lesser reduction in ml per minute. Average rates of electrolyte ex- chloride excretion was observed. In the first six cretion in the first 190 minutes were: Na+, 324; of the seven experiments (Tables I and II), chlo- KF, 106; and Cl-, 424 fuEq per minute; in the ride excretion was reduced by from 21 to 66 per latter 160 minutes: Na+, 411; K+, 70; and Cl-, 355 cent of the control values and the decrements in ,uEq per minute. These control studies are in rate of chloride excretion ranged from 14 to 657 agreement with the previous work of other in- ,uEq per minute in these six experiments. In one vestigators (21-23). Altogether, these results experiment (J.O. on 20 g NaCl intake), the fall appear to exclude the possibility that the observed in chloride excretion after aldosterone actually ex- alterations in electrolyte excretion after aldosterone ceeded the fall in sodium output by a considerable were simply a consequence of prolonged water degree. The reason for this single observation diuresis. remains obscure. Effect on potassium excretion and on urinary That the changes observed in sodium and chlo- pH. In every experiment but one (M.U., salt- ride excretion were due to aldosterone and not depleted) potassium excretion was at least transi- to prolonged water diuresis is evident from data ently increased. The increased potassium excre- obtained in two control studies. Water diuresis tion often preceded the sodium chloride retention

TABLE III Detailed protocol of a typical control experiment *

Plasma Time V Uosn Cosm CH20 UNNV UCIC UKV Osm Na K Cl min ml/min iAOsm/ml ml/min ml/min AEq/min IEq/min AEq/min AOsm/ml AEq/ml AEq/ml AEq/ml 0 1,500 ml H20 p.o., 30 minutes before start of infusion to recumbent subject. 5% Dextrose and water infusion at 18 ml/min. +23 to 67 17.4 47 2.9 14.5 299 269 29 287 146 4.5 103 +67 to 105 18.2 45 3.4 14.8 184 212 33 +105 to 149 17.1 42 2.5 14.6 189 159 31 +149 to 209 18.2 42 2.7 15.5 212 175 25 +209 to 231 17.0 43 2.6 14.4 192 169 26 +231 to 252 17.2 43 2.7 14.5 211 208 24 275 3.9 108 +252 to 280 17.1 44 2.7 14.4 212 187 23 +280 to 317 17.1 43 2.7 14.4 204 186 25 +317 to 340 17.3 40 2.6 14.7 223 201 29 +340 to +360 14.8 45 2.5 12.3 170 154 34 270 140 4.0 109 Infusion completed. * Subject O.G., 71 kg white male on normal NaCl (approx. 6.0 g/day) intake. 908 EDMUND H. SONNENBLICK, PAUL J. CANNON AND JOHN H. LARAGH as that which occurs in prolonged water diuresis. 20O 0 c0. Therefore, the effects of aldosterone were ob- co CI 00O served 15 during the descending limb of water diuresis. Cosm JO\ el/. The changes in total solute excretion after (ml/min) 10 aldo- 5, sterone paralleled the changes in sodium excretion JO \\3 5 both in magnitude and in phase. Thus, after an MUmuSH MUmu~, initial delay of from 20 to 60 minutes a progres- 01 I sive and marked reduction in urinary osmolarity 5 10 15 20 25 30 35 ensued reaching a nadir 2 to 4 hours after the * Control CFH20 o Aldosterone aldosterone administration. Urinary osmolarity (ml/min) fell to levels well below that which would be ex- FIG. 3. EFFECT OF INTRAVENOUS ALDOSTERONE ON THE pected from water diuresis alone (21-23) (20 RELATION OF OSMOLAR TO FREE WATER CLEARANCE DURING /Osm per ml). Thus, aldosterone facilitated the A MAINTAINED WATER DIURESIS. Plotted from control formation of an extremely dilute urine with an in- periods taken at the height of water diuresis and from creased urine/plasma osmolar gradient. The an average of two or three experimental periods at the peak of aldosterone effect. After aldosterone the decre- urine/plasma sodium concentration gradient in- ment in osmolar clearance approaches or is equal to the creased markedly in like manner. increment in free water clearance in most of the studies. As was the case with sodium chloride excretion, The rise in free water clearance occurs in the face of a the total solute excretion did not fall appreciably falling osmolar clearance. The findings suggest that in the sodium-depleted subject. However, in the aldosterone abstracts sodium chloride from the urine without water. other six studies total solute concentration was reduced by from 49 to 67 per cent of control values. A similar reduction in the total solute and persisted during the periods of maximal so- clearance (Cos,n ) was thus observed. dium retention in only four of the seven experi- Since the urine flow did not change appreciably ments (Tables I and II; Figures 1 and 2). while the osmolar clearance decreased markedly, The magnitude of the increased potassium ex- an increase in free water clearance was produced cretion produced by aldosterone (,A UKV) was by aldosterone. In the first six experiments, the small, ranging from + 12 to + 40 uEq per min- free water clearance was increased by from 1.1 to ute or from + 17 to + 30 per cent of the control 4.3 ml per minute, but in the sodium-depleted values. The increments in K+ excretion were of subject, M.U., the observed changes were again similar degree in all studies and were of consider- slight. Since the urine flow was not rising, the ably lesser magnitude than the decrements ob- calculated increases in free water cannot be at- served in sodium chloride excretion. tributed to an increasing water diuresis, and be- The urinary pH was observed to fall following cause solute excretion was falling, they cannot be aldosterone excretion (Tables I and II). The the result of an increased solute load (24). Hence, average observed fall was 0.38 pH units at the these results imply the hypertonic abstraction of peak of the action of the hormone on total solute solute from the urine, i.e., reabsorption of solute excretion. unaccompanied by isosmotic amounts of water. Effect on urine flow, total solute clearance and In Figure 3 the relationship between the os- free water excretion. In all studies aldosterone molar clearance and the free water clearance be- was administered only after the peak of water diu- fore and after aldosterone for all seven experi- resis had been achieved. The control rate of urine ments is plotted. It can be seen that after aldo- flow varied considerably in different subjects from sterone the fall in solute clearance (A CO--1M) is 10 to 45 ml per minute. These individual varia- equal to, or almost equal to, the rise in free water tions in urine flow seemed to be related to the clearance (A C1120). In fact, in four studies of variations in filtered load of solute (24). After Subjects M.U. and S.H., 1 ml of free water was aldosterone administration, the urine flow either added to the urine for each milliliter of urine did not change or showed a slight decrease, such cleared of solute. This implies that aldosterone ALDOSTERONE AND URTINARY DILUTION 909 caused the virtually totally selective abstraction findings of other investigators. Thus, the delayed of solute without water from the tubular urine. onset of action (3. 7, 25-29), the lack of effect on Relationship of changes in sodium and chloride renal hemodynamics (2, 28, 30), the sodium and clearances to changes in osmnolar clearance. Be- chloride retention, and the kaliuresis of aldosterone cause in normal individuals sodium and chloride (1-13) have all been described under a variety are the major osmolar constituents of urine and of experimental and clinical conditions. plasma and comprise the bulk of the filtered load, In the present study a latent period of about these solutes are the only ones available for tu- 20 to 60 minutes was observed before there was bular reabsorption in amounts sufficient to ac- any demonstrable effect of the hormone on so- count for most of the free water generated during dium excretion. The peak effect occurred in 2 water diuresis (13). Therefore, one might as- to 4 hours, and the action lasted for as long as 6 sume that the changes in osmolar and free water to 8 hours after administration. In previous stud- clearance produced by aldosterone were due to ies of man, other investigators have also noted the effects of the hormone on sodium (and chlo- a similar latent period and a similar duration of ride) ; and, in fact, in all experiments, changes in activity (3, 7, 25). Moreover, Barger, Berlin UNaV and in Uc1V closely paralleled changes in and Tulenko (26) and Ganong, Mulrow and Hol- UOSMV. Aldosterone caused alterations in sodium linger (31, 32), utilizing renal artery infusions, and chloride excretion of such magnitude that, for and Crabbe (27), utilizing an isolated toad blad- the most part, alterations in Co0M produced by the der, have also noted the delayed onset of action hormone can be interpreted largely in terms of of the hormone. these ions. Mineralocorticoids such as desoxycorticosterone In an effort to relate graphically the effect of and aldosterone, in short-term studies, do not ap- aldosterone on sodium excretion to that on solute pear to alter renal hemodynamic function either excretion (Figure 4), twice the CXa 2 caused by in experimental animals (28-33) or in man (34- the hormone has been plotted against the Cosm 36). In the present study aldosterone did not caused by the aldosterone for all experiments, produce significant changes in the renal plasma with a resultant linear relationship. It can be flow or in the glomerular filtration rate. There- seen that the changes of Cosm and thus of free water can be interpreted to be mainly a result of the effect of aldosterone on sodium (with equiva- 12 lent anions). Hence, it can be concluded II // that 10 / aldosterone produced a fall in and C0511, a rise in 9 / CH2O by the abstraction of salt from a distal por- 8 / tion of the nephron. 2 ACN 0)/ Effect on urea excretion. In all experiments, 7 /MO the urea clearance declined gradually with no 5/ acute change observed following aldosterone ad- 4/ ministration. These data are not given in the Ml/min~~ ~ COj m/~ 2 / tables. IM / SH

DISCUSSION 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A number of the observations made in the ACOSM Mlmi/m present study appear to confirm and extend the FIG. 4. RELATIONSHIP BETWEEN THE CHANGE IN OS- MOLAR CLEARANCE AND TWO TIMES THE CHANGE IN SODIUM 2 For a A C..,. of 1 ml, 1 X Po..1 (approximately 280 CLEARANCE PRODUCED BY ALDOSTERONE. Two times the gOsm) was abstracted from tubular lumen. For a A CNa decrement in sodium clearance after aldosterone ad- of 1 ml then, 1 X PNa (approximately 140 /LEq) of Na' ministration is plotted against the corresponding decre- was abstracted. Each microequivalent is an osmotically ment in osmolar clearance produced by the hormone. active particle. In abstraction of Na+ an equivalent num- The plot illustrates that the observed changes in osmolar ber of anions, also osmotically active particles, was re- clearance produced by the hormone are largely accounted moved. Hence, to relate A CNa to A COSm, one must mul- for by a similar change in sodium reabsorption with tiply A CNa X 2. attendant anion. 910 EDMUND H. SONNENBLICK, PAUL J. CANNON AND JOHN H. LARAGH fore, it would appear that the observed effects on can cause the abstraction of sodium chloride with- electrolyte and water excretion are the result of out water from the tubular urine, a finding which induced alterations in the activity of tubular trans- has not been reported heretofore.3 During main- port systems. tained water diuresis aldosterone caused the re- The intravenous administration of aldosterone moval of sodium chloride from the urine, produc- caused increased tubular reabsorption of sodium ing a fall in osmolar clearance while urine flow chloride and a kaliuresis. The increased potas- was maintained; this resulted in a concomitant sium excretion often began prior to salt retention, rise in free water clearance. For Subjects S.H. was relatively small in degree, and at times had and M.U., the relationships between solute ab- ceased before the sodium retention had reached straction and free water formation were such its peak. Similar effects of aldosterone have been (Figure 3) as to suggest that salt was abstracted described both during acute administration (2, 7, virtually without water. However, in Subject J.O. 25, 26, 31-33) and in more prolonged balance the increment in free water clearance was less studies (1, 3-6, 37). than the decrement in osmolar clearance indicating In the present study aldosterone usually caused that, in this subject, in addition to selective so- sodium retention in excess of chloride, confirming dium chloride reabsorption, some additional isos- the results of August and Nelson (7), who ad- motic reabsorption may also have been induced. ministered aldosterone intravenously with iso- Previous studies have indicated (24, 39, 40) tonic saline infusions. It thus appears that aldo- that, during water diuresis, there is a direct rela- sterone acted to augment the active renal tubular tionship between solute excretion and free water reabsorption of sodium ion with chloride. Prece- clearance, a rise in Cosm resulting in a rise in CHO- dent for the stimulation of active sodium trans- Therefore, the rise in free water clearance noted port by aldosterone has been found in vitro by after aldosterone may have more significance be- Crabbe (27), using an isolated toad bladder. cause it occurred in the face of a falling solute ex- According to present concepts (38), filtered cretion. Further, because the hormone was ad- potassium is completely reabsorbed before the po- ministered only after a peak of water diuresis was tassium destined for excretion is secreted into the achieved, when urine flow was either stable or de- tubular urine by a distal Ki for Na+ ion exchange clining, the increment in free water excretion after process. However, while the kaliuresis observed aldosterone administration cannot be simply the in these experiments may have resulted from an result of an increasing water diuresis. acceleration of this ion exchange mechanism, con- Because aldosterone facilitates net abstraction of siderable evidence indicates that the predominant sodium chloride without water from the urine, it effect of aldosterone-i.e., to cause sodium and thus appears to act in the nephron at a locus dis- chloride reabsorption-occurred independently of, tal to the site of isosmotic reabsorption. The con- and at a different locus in the distal nephron from cept that free water is formed in the more distal the K+ for Na+ ion exchange process. Thus, the tubular segments by selective reabsorption of kaliuresis in general was not temporally related to solute without water is well supported by a number the sodium retention, the magnitude of the kaliure- of studies (14-17). Micropuncture studies have sis was far less than the sodium retention, and shown that in the proximal tubule, sodium reab- the degree of kaliuresis in each subject was not sorption is isosmotic (14-16), while fluid from related to the corresponding degree of sodium re- the early distal tubule has been found to be hypo- tention. Ion exchange, Na+ for K+, does not ex- tonic regardless of whether the final urine is plain the significant chloride retention which oc- hypo-or hyperosmotic (16). Vander and co- curred concomitant with sodium reabsorption. workers, using a stop-flow technique (41), have Furthermore, ion exchange does not explain the reported that in adrenalectomized dogs, aldo- reduced osmolarity of the urine after administra- sterone increased the maximal concentration gra- tion of the hormone, since the observed decrements by in NaCl excretion were, in fact, accompanied 3 Dingman and associates measured the osmolar clear- comparable reductions in total solute excretion. ance during infusion of aldosterone. However, water di- The present study demonstrates that aldosterone uresis was not maintained in these studies (2). ALDOSTERONE AND URINARY DILUTION 911 dient for sodium which could be developed be- but this effect was often temporally dissociated tween the plasma and distal tubular urine. from the major action of the hormone, which was Because the hormone caused a distal abstrac- to cause sodium and chloride retention. tion of salt without water from the urine, an in- After aldosterone administration urine flow creased plasma/urine sodium concentration gradi- either did not change or declined slightly; the ent was formed and the urine became more dilute. osmolar clearance was reduced, and hence the free The results thus suggest that aldosterone is con- water clearance was increased. In some of the cerned with the production of a hypotonic urine. studies, the decrement in osmolar clearance ap- Inferential support for this role of aldosterone in proached or was equal to the increment in free urinary dilution may be derived from previous water clearance produced by the hormone. studies of electrolyte and water metabolism in The results suggest that, under circumstances adrenalectomized dogs (29, 30, 42, 43) and in of water diuresis, aldosterone can promote net patients with adrenal or pituitary insufficiency abstraction of sodium chloride from the urine, (35, 44, 45). In this group a characteristic pic- virtually without water, in a distal portion of the ture is seen with low glomerular filtration, in- renal tubule. creased loss of sodium chloride (43), and a defi- The action of aldosterone results in the crea- cient ability to excrete a water load (47). Min- tion of an increased plasma/urine sodium con- eralocorticoid (46) alone, while promoting salt centration gradient and the formation of a more retention, does not repair the defect in water ex- hypotonic urine. It is therefore suggested that cretion. Cortisol (20, 30, 44, 46) increases the fil- the hormone plays a role in urinary dilution. tration rate, increases filtered sodium load, and allows more salt to be reabsorbed from the dis- REFERENCES tal tubule with the production of free water and 1. Mach, R. S., Fabre, J., Duckert, A., Borth, R., and the excretion of a more dilute urine. However, Ducommun, P. Action clinique et metabolique de this process is not very efficient, and although the l'aldosterone (electrocortine). Schweiz. med. ability to excrete water is improved, this occurs Wschr. 1954, 84, 407. at the expense of substantial urinary wastage of 2. Dingman, J. F., Finkenstaedt, J. T., Laidlaw, J. C., Renold, A. E., Jenkins, D., Merrill, J. P., and sodium chloride. 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