COMPOSITION OF THE RENAL MEDULLA DURING WATER DIURESIS
Howard Levitin, … , Gilles Pigeon, Franklin H. Epstein
J Clin Invest. 1962;41(5):1145-1151. https://doi.org/10.1172/JCI104567.
Research Article
Find the latest version: https://jci.me/104567/pdf Journal of Clinical Investigation Vol. 41, No. 5, 1962 COMPOSITION OF THE RENAL MEDULLA DURING WATER DIURESIS * By HOWARD LEVITIN,t ALVIN GOODMAN,* GILLES PIGEON § AND FRANKLIN H. EPSTEIN 11 (From the Department of Internal Medicine, Yale University School of Medicine, New Haven, Conn.) (Submitted for publication December 7, 1961; accepted January 15, 1962) During antidiuresis, sodium is concentrated in tubules in kidney sections from rats undergoing the papilla and medulla of mammalian kidneys as water diuresis was lower than that of cortex (3). a result of active sodium reabsorption from medul- Finally, direct micropuncture of loops of Henle lary tubules and countercurrent flow through the and vasa recta in hamsters with diabetes insipidus loops of Henle and the medullary capillaries. It yielded fluid with an osmolality higher than that is clear from chemical (1) and cryoscopic (2, 3) of vena cava plasma but lower than that observed analysis of sections of kidney, and from direct mi- in normal animals excreting a concentrated urine cropuncture (4-6), that under these circumstances (6). the osmolality of medullary interstitial fluid is ap- The present experiments were designed to clarify proximately that of collecting-duct urine and that the action of antidiuretic hormone on the sodium sodium concentration rises progressively along a content of the renal medulla. The chemical com- gradient from cortex to medulla. position of papilla, medulla, and cortex of dogs The precise role of antidiuretic hormone (ADH) was measured during hydropenia, during water in establishing and maintaining this gradient is not diuresis, and at varying intervals after the infusion entirely clear, partly because comparable studies of vasopressin. The results confirm previous evi- in the absence of vasopressin (i.e., during water dence that medullary fluid is hypertonic during diuresis) have been more difficult to accomplish. water diuresis, although not as concentrated as Ullrich, Jarausch and Drenckhahn demonstrated during hydropenia. They further indicate that, that the osmolality and sodium concentration of in addition to the fall in sodium concentration ex- papillary water approached that of peripheral pected as a result of an increase in water content., plasma in dogs during water diuresis (1, 7). water diuresis is associated with a decline in the That medullary interstitial fluid is actually hyper- absolute amount of sodium per unit of dry solids tonic to plasma in the absence of ADH was sug- in the renal medulla. The latter is restored by in- gested by the demonstration (8) that compression fusions of vasopressin or by dehydration. The of the renal artery of one kidney during water data suggest that, in addition to increasing the diuresis led to production of hypertonic urine by permeability of the collecting ducts to the back- that kidney. Recently, Bray reported that the diffusion of water, ADH enhances the sequestra- melting point of the contents of small medullary tion of sodium in the interstitial fluids of medulla and papilla. * Aided by grants from the American Heart Associa- tion, the National Heart Institute (H-834), the National METHODS Institute of Arthritis and Metabolic Diseases (2A-5015), Unanesthetized female mongrel dogs weighing 8 to 13 and the Lawrence Gelb Foundation. kg were trained to lie quietly with a urethral catheter in tEstablished Investigator of the American Heart place. Their standard dog ration was supplemented with Association. half a pound of horsemeat daily. All of the animals had t Postgraduate Fellow of the U. S. Public Health been previously tested and were not used if their urinary Service. osmolality after 24 hours of dehydration did not exceed § Traveling Fellow of the R. Samuel McLaughlin 1,400 mOsm! per kg of water. Foundation, 1960-1961; Research Fellow of the Connecti- Four groups of dogs were studied. The first group (6 cut Heart Association, 1961-1962. dogs) was studied during a water diuresis which had been 11 During the tenure of an Established Investigatorship induced 2 hours earlier by the intragastric administration of the American Heart Association. of water amounting to 5 per cent of their body weight. 1145 1146 LEVITIN, GOODMAN, PIGEON AND EPSTEIN
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Group 2 (5 dogs) and group 3 (5 dogs) received a similar water load, followed 2 hours later, at the height of the en- suing water diuresis, by the intravenous infusion of vaso- pressin at the rate of 50 mU per kg per hour. Group 2 received the vasopressin infusion for 30 minutes, and group 3 received the vasopressin infusion for 2 hours. Group 4 (6 dogs) was studied during antidiuresis which resulted from 24 hours of food and water deprivation. In all dogs, timed urine collections were obtained prior to the conclusion of the experiment, at which time an intravenous injection of pentobarbital was given, and both kidneys were removed in 1 to 2 minutes. The pelvis of the kidney was opened and the longitudinal papillary ridge was exposed. A thin strip of this ridge WATER 30 MIN 2 HRS 24 HRS DIURESIS p ADH p ADH DEHYD. (papilla), 2 mm in thickness, was cut. A deeper longi- (6) (5) (5) (6) tudinal strip (medulla), 4 mm thick, was then dissected free. The capsule was stripped and pieces of cortex ob- FIG. 1. PAPILLARY CONTENT OF SODIUM AND POTAS- tained. Duplicate samples of papilla, medulla, and cortex SIUM PER 100 G DRY SOLIDS DURING WATER DIURESIS AND were examined. One sample was weighed by tare to con- AT VARYING STAGES OF ANTIDIURESIS. stant weight for water content. The other sample was ground in electrolyte-free, fine mesh carborundum and di- ture at the time the kidneys were clamped; in these cases luted with 7 ml of water (papilla and medulla) or 10 ml the specific activity of plasma sodium corresponded of water (cortex) and analyzed for sodium, potassium, closely to that of the sodium of renal cortex, suggesting ammonia, and urea, employing techniques previously pub- that in analyzing the data the specific activity of medul- lished (9). The average weight of the samples was as fol- lary or papillary sodium might conveniently be referred lows: papilla, 138 mg; medulla, 390 mg; cortex, 291 mg. to that of cortex. Four dogs were studied during water Urine samples were analyzed for the same solutes, as well diuresis and 5 after 24 to 48 hours of dehydration. as for osmolality, with a Fiske osmometer. In order to eliminate possible artifacts arising from losses of blood and interstitial fluid from the severed pedi- RESULTS cle of an unclamped kidney (10), two further groups of 5 dogs each were studied-one group during water diure- Composition of papilla, medulla, and cortex of sis and the other during hydropenia. In these experi- unclamped kidneys (Table I, Figure 1). The con- ments the renal pedicle was occluded with two large centration of solutes in tissue water [calculated as clamps. The renal artery, vein, and ureter were cut, and the sum of the concentrations of urea + 2(Na + the kidney with attached pedicle clamp was immediately K + increased frozen in acetone and dry ice. Cross sectional cuts near NH4)] progressively from cortex the middle of the frozen kidney were made with a power- to papilla in dehydrated dogs. This gradient was driven scroll saw. Duplicate samples of papilla, medulla, markedly reduced during water diuresis, a result and cortex, weighing an average of 169, 218, and 783 mg, of decreases in the concentration of sodium and respectively, were obtained. One sample was weighed by urea. Nevertheless, at the height of water diure- tare and dried to constant weight for water content. The sis, while the kidneys were elaborating a urine of other sample was placed in a weighed 10-ml volumetric flask to which 4 ml of concentrated nitric acid was added. concentration below 100 mOsm per kg, papilla Digestion was accomplished for 24 hours on a steam and medulla were distinctly hypertonic to plasma table, after which the clear nitric acid digest was brought (average 381 and 401 mOsm per kg, respectively, to volume and analyzed for sodium and potassium. Urea while mean plasma osmolality was 285 mOsm per and ammonia were not determined in this series of ex- It is of periments. kg). interest that under these circum- In order to estimate the rate of turnover of medullary stances the concentration of sodium and of total sodium during water diuresis and during hydropenia, 0.04 solutes was consistently slightly higher in water of to 0.09 /Ac of Na22Cl per kg of body weight per minute the inner medulla than at the papillary tip, in con- was infused intravenously into trained, unanesthetized trast to the pattern seen in hydropenia. dogs, using a syringe-type, constant infusion pump. At The quantity of sodium per unit of dry solids 3 to 4 minutes after the beginning of the infusion, samples of papilla, medulla, and cortex were analyzed for sodium (DS) declined significantly in papilla and medulla as described above, after their radioactivity had been during water diuresis. When water diuresis was measured in a y-ray, well-type scintillation counter. In interrupted by infusing vasopressin, sodium content some experiments blood was obtained by cardiac punc- of papilla per 100 g of dry solids rose progressively 1148 LEVITIN, GOODMAN, PIGEON AND EPSTEIN (Figure 1). Papillary sodium was higher in dogs
00 OF killed after 2 hours of vasopressin infusion than (S -H after 30 minutes, and was higher still after 24 '0 hours of dehydration. The rate of urine flow was N -H 4 similar in all three groups of antidiuretic animals. Cortical sodium was little affected by the transi- x ,o tion from diuresis to antidiuresis. Tissue potas- 0 b4040 u o sium tended to decrease slightly when water diu-
0) -H -H resis was replaced by antidiuresis. io6 0o-00 te seems 0o 0 It unlikely that changes in the concen- C0 tration of sodium and potassium in the urine con- i-i 0) N tributed importantly to the observed changes in 00 if)
0 tissue content of these ions. Bray estimated the x' volume of urine in segments of papilla from anti- m2X . i4 diuretic kidneys of dogs at not more than 5 per 00) if -H cent of the water of tissue ( 11 ). Despite a change .X 00 X0 in potassium concentration in the urine from 6 mEq per L during water diuresis to 160 mEq per _4 e ---U) 0- el; L during antidiuresis, there was no increase in medullary potassium. '0.; V ._ before analysis contained more water and sodium "0 CZ than those processed by the usual technique, while 11 M: ._! C -H -H 0) potassium was unaffected. The increase in water NI 81 a a) N content was most pronounced in the cortex of both X on w0 a1 'o diuretic and antidiuretic kidneys. These observa- ~ - ..d t, tions are consistent with those of Swann and co- '0 workers (10, 12) and Hanssen (13), who called -) toI 14 of 00 attention to the prominence of the interstitial space * 0i 0 0 in the cortex of kidneys clamped and frozen be- tf) 0) fore sectioning. '0i N,- (, * 0 When compared with kidneys from dehydrated 0o -H -H To N To 4 Q+ (1 > dogs, water diuresis was again clearly associated with a decrease in the quantity of sodium per 100 g -H -H of dry solids in the renal papilla and medulla. Perhaps as a result of increased distention with Z-z -H -H Cd extracellular fluid, sodium content of cortex, re- U, ferred to dry solids, was actually higher during water diuresis than in hydropenia. Histological of - sections frozen kidneys were * e fixed by a freeze-substitution technique. Portions of of medulla were examined with particular atten- .0 C'4N 00 (-4 oS ; o 6 i Cd.W= TABLE 111 Relative specific activity of sodium in various portions of the dog kidney after injection of Na22 Specific activity Sodium content Papilla/ Medulla/ Duration of cortex cortex Uo0m Papilla Medulla Cortex Na'2 infusion mOsmlkg mEq/100 g DS min Dehydrated 0.348* 0.455 1686 136.6 140.6 31.3 3.43 5 dogs 40.145 ±0.147 4:530 i117.4 ±22.3 46.9 ±0.36 Water diuresis 4 dogs 0.539 0.679 67 106.4 116.8 36.2 3.64 ±0.177 ±0.104 ±21 ±29.5 ±9.4 +6.6 +0.45 p <0.05 <0.01 <0.01 <0.05 < 0.02 NSt NS * Mean i standard deviation. t NS =not significant. medulla, as compared with cortex, was signifi- this action of posterior pituitary hormone. It is cantly more rapid in dogs undergoing water diu- conceivable that active reabsorption of sodium resis than in dogs excreting a maximally con- chloride from the ascending loop of Henle is ac- centrated urine. celerated by ADH, resulting in an increased depo- sition of sodium salts in medullary interstitial DISCUSSION fluid. Active transport of sodium by frog skin and toad bladder is enhanced by vasopressin (15, These experiments add to the accumulating evi- 16). Although infusions of vasopressin have not dence that, in the absence of ADH, medullary in- been shown to decrease sodium excretion, the terstitial fluid is hypertonic, although not as total quantity of sodium necessary to raise the strongly so as when a maximally concentrated content of sodium of the medulla from that ob- urine is being excreted. Calculated osmolality of served during water diuresis to that present dur- tissue water in medulla and papilla was about 400 ing hydropenia is very small (40 /LEq per minute mOsm per kg in water-loaded dogs. These for only 10 minutes, in a dog with kidneys weigh- values are similar to those obtained by Gottschalk ing 50 g each). Such a transient diminution in in fluid aspirated from the loop of Henle and the urinary excretion of sodium would be difficult to vasa recta of the papilla in hamsters with diabetes detect. insipidus (6). It would seem that the counter- A second possibility is that ADH decreases the current mechanism for concentrating sodium in rate of removal of sodium from the medulla by di- the medulla continues to operate, although at re- minishing medullary blood flow. Circulation time duced efficiency, during water diuresis. through the medulla has in fact been shown to be It was suggested by Kiil and Aukland (14) shortened by water diuresis and prolonged by that more water is actually reabsorbed from the vasopressin (17). The observation that urinary medullary collecting ducts during water diuresis oxygen tension is elevated by water diuresis (18) than during hydropenia, since in the former state, is also compatible with the hypothesis that blood large volumes of dilute urine, unable to equilibrate flow through the countercurrent arrangement of with isotonic interstitial fluid in the distal con- capillary loops in the medulla is depressed by hy- voluted tubules, are delivered to the medulla. dropenia and increased in the absence of ADH. Under these circumstances one might expect the Such an increase in blood flow through the medulla concentration of sodium in medullary fluid to be during water diuresis might result either from the diluted. The present experiments show clearly removal of a vasoconstrictive action on the vasa that the absolute amount of sodium in medulla recta induced by vasopressin itself, or from in- and papilla, as well as its concentration in tissue creased diffusion of water back through the col- water, is depressed by water diuresis and increased lecting ducts, as a consequence of the delivery of a by ADH. larger volume of dilute urine to the medulla. Several possible mechanisms might account for Studies of the rate of turnover of sodium in me- 1150 LEVITIN, GOODMAN, PIGEON AND EPSTEIN dulla and cortex were undertaken in an attempt ACKNOWLEDGM ENTS to clarify these questions. When radioactive so- The authors are especially grateful to Dr. Michael dium was infused, the rate of enrichment of medul- Kashgarian for preparing and examining the histological lary sodium was accelerated during water diure- sections. Mrs. Eva Taborsky and Mrs. Nadia Mykety sis and retarded during antidiuresis. 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