(Received 27 September 1937)

Transcription

1 222 J. Physiol. (I937) 9I, I 6I2.46I:6I THE SECRETION OF URINE IN MAN DURING EXPERIMENTAL SALT DEFICIENCY BY R. A. McCANCE AND E. M. WIDDOWSON From the Biochemical Laboratory, King's College Hospital, London, S.E. 5 (Received 27 September 1937) IT has been recognized by clinicians for some time that the blood urea may rise to very great heights in diseases which are not "nephritis" in the usual sense of the term. This is particularly true of diseases in which there is a fall in the plasma electrolytes, particularly the chlorides. The causal connexion, if any, is still far from clear and very few attempts have been made to solve the matter experimentally. Hitherto, no experimental work has been done on man. The subject was reviewed by Kerpel-Fronius [1936] and McCance [1936b] and no great advance in knowledge appears to have been made during the past year. It will only be necessary, therefore, to refer to papers with a direct bearing on the matter in hand. In the present investigation five normal male adults have been made salt deficient by diet and sweating [McCance, 1936 a, b]. Their kidney function has been studied before, during, and after the deficiency, but the tests employed have varied somewhat from one subject to another. This will be made clear in the presentation of the results. The subjects were not confined to bed while tests were being made, but their activity was restricted to quiet movement in the laboratory. The chemical methods were the same as those employed by McCance & Widdowson [1937]. Cane sugar, which was not used in that investigation, has been determined in the same way as inulin. RESULTS (1) The blood ureas During the experiments on R.A.M. and R.B.N. blood was collected almost every day at about noon for the determination of the blood urea. The findings are shown in Fig. 1. It is perhaps well to emphasize that

2 SALT DEFICIENCY AND URINE SECRETION 223 although the salt deprivation was being brought about by sweating, and although salt deficiency in man is accompanied by anhydroemia, both of these subjects were drinking enough water to maintain their urine volumes at or above their normal levels. A diminished urine flow, therefore, was not the cause of the rise of the blood urea. It will be observed that during the recovery period the blood urea fell below its original level o30 o 50 - C3 ~40- ~20-10 Period of progressive deficiency Period of recovery Days Fig. 1. Behaviour of the blood urea during and after salt deficiency. o--o R.B.N. x - x R.A.M. This has been observed in the other subjects and is probably part of a general tendency of the body towards overcompensation during the recovery period. It is certainly not due to a diminished protein intake, and should rather be compared with the fall in the hiemoglobin and red blood cells to subnormal values which has always been found at about the same time [McCance, 1937]. (2) The concentration of urea in the urine No deliberate attempt was made to measure the ability of the kidney to concentrate urea or to produce a urine of high osmotic pressure. The observations which have been made suggest that its ability was not impaired. R.A.M. on several occasions had concentrations of urea of p.c. in his urine when he was salt deficient and higher concentrations have not been observed in this subject even when normal. One of R.B.N.'s 24 hr. urines, which had an unusually small volume, contained 3 p.c. of urea, and J.T.B. passed a specimen of urine containing 3*96 p.c. of urea when his blood urea was over 80 mg./100 c.c.

3 224 R. A. McCANCE AND E. M. WIDDOWSON (3) The excretion of water It became evident early in the investigation that the water metabolism of the salt deficient subjects was not normal. In the induction of a state of salt deficiency the removal of salt from the body was always followed by a loss of weight (presumably water). When the deficiency was well developed, however, the removal of further salt did not as a rule lead to a loss of weight [Mc Cance, 1936 a, b]. It was observed by most subjects at this stage that it was extremely hard to provoke a diuresis; ingested water was not excreted within the usual time and sometimes was retained for many hours. J.T.B. for example after emptying his bladder before lunch on 16 January weighed 87 kg. (naked). During the afternoon he lost 2080 g. by sweating and drank 1000 c.c. in the hot air bath. His net loss of water therefore was only 1080 g. He drank a considerable quantity of liquid during the evening and next morning in order to ensure a urine flow of more than 2 c.c./min. for the kidney function tests planned for the afternoon of the 17th. In spite of this his urine volume for the 24 hr. (1 p.m. to 1 p.m.) was only 550 c.c. and his naked weight at 1 p.m. on the 17th was kg., an increase of nearly 1000 g. Owing to nausea his food intake had been rather meagre, so this could not have been responsible for his increase in weight. The volumes during the kidney function tests were about 1 c.c./min. Other subjects managed to produce a much greater diuresis than this, but the highest rate of flow recorded in these salt deficient subjects has been 5-83 c.c./min. Minute volumes of more than 12 c.c. could always be obtained with ease when the subjects were normal. These results corroborate those of Baldes & Smirk [1934] who found that 1 litre of water provoked a subnormal diuresis in human subjects who had been made salt deficient. These authors employed diet and sweating to produce the deficiency which, however, was probably much less severe than that in the present subjects. (4) The urea clearances In the first two experiments (on R.A.M. and R.B.N.) a 2-hourly specimen of urine was collected almost every day before lunch, no attempt being made to produce a large diuresis. The clearances were calculated as a percentage of "normal" by the standard or maximum formula and their course is shown in Fig. 2. It will be noted that R.B.N.'s preliminary clearances were well over 100 p.c., they fell to p.c. of normal during salt deficiency, and returned to their original level at the end. R.A.M.'s were about 100 p.c. at first, they fell to about 70 p.c. and passed through a supernormal phase after the deficiency period was over. R.A.M.'s

4 SALT DEFICIENCY AND URINE SECRETION 225 clearances fell to much lower levels than those shown in Fig. 2 (32-36 p.c. of normal) during the 3-5 hr. following sweating in the hot air bath. His daily excretion of urea was much lower than it should have been considering the level of urea in his blood. This was demonstrated by 180 F~ c.120. Ca C) '80 60 Fig Period of rop sv fce Period of Irecovery Days Behaviour of the urea clearances (expressed as a percentage of normal) during and after salt deficiency. o-o R.B.N. x - x R.A.M. another experiment in which the subject ate about 250 g. of protein a day for 5 days. This raised his blood urea to similar levels, but also increased rather than decreased his urea clearances (Table I). Presumably TABLE I. A comparison of R.A.M.'s urea clearances while salt deficient and while on a very high protein intake A. Blood urea Urea clearance mg. per 100 c.c. p.c. of normal During a very high protein intake, ~~~A Blood urea Urea clearance mg. per 100 c.c. p.c. of normal * Cope [1933] failed to lower the urea clearances by reducing the salt content of the body because his measures to effect the latter were comparatively mild. In the other subjects urea clearances were not determined daily but only during the times when the creatinine, sucrose and inulin clearances were being carried out. These will now be described.

5 226 R. A. McCANCE AND E. M. WIDDOWSON (5) Clearances of substances without significant "augmentation" limits (a) Creatinine clearances. These were determined on four subjects, R.B.N., D.W., J.T.B. and R.M.L. Two to six experiments were carried out on each subject. Normal experiments were performed before and after the period of deficiency, except in the case of J.T.B. on whom only one normal experiment was carried out. In each experiment R.B.N. and D.W. took 5-6 g. of creatinine by mouth about 1-1 hr. before the clearances were carried out. The creatinine was injected intravenously into J.T.B. and R.M.L. as a 3 p.c. solution in distilled water. The collection periods began min. after the injection was finished. Urines were collected as a rule in half-hourly periods and four to eight specimens were obtained in each experiment. The subjects were not catheterized but were all able to empty their bladders without difficulty when specimens were required. Blood was taken by vein puncture half-way through each period. Coagulation was prevented by heparin and the corpuscles were separated from the plasma within a few minutes of taking the blood. The results are shown in Table II. It will be seen that in each subject TABLE II. The creatinine clearances during health and during salt deficiency Normal health clearance Clearance, clearance Clearance, periods c.c./mim. periods c.c./min. experi- in each Average and experi- in each Average and Subject ment experiment range ment experiment range R.B.N ( ) ( ) ( ) ( ) ( ) ( ) D.W ( ) ( ) ( ) ( ) ( ) - J.T.B ( ) ( ) R.M.L ( ) ( ) ( ) ( ) there was a considerable fall in the creatinine clearances during salt deficiency. In most cases there was no overlapping of the normal and salt deficient ranges. (b) Sucrose. This substance was used as a guide to glomerular filtration rates on one subject only, D.W. At this time inulin had just been found to be extremely toxic [Mc Canc e, 1936 b] and no method for its purification was available [Goldring & Smith, 1936]. 50 g. were given intravenously as a 25 p.c. solution in distilled water over a period of 30 min. The injection terminated at least half an hour before the collection

6 SALT DEFICIENCY AND URINE SECRETION 227 TABLE III. The cane sugar clearances of D.W. during health and during salt deficiency Normal health A A A clearance Clearance, clearance Clearance, periods c.c./min. periods c.c./min. experi- in each Average experi- in each Average ment experiment and range ment experiment and range ( ) (70-86) ( ) (62-94) ( ) periods began. Creatinine and urea clearances were determined simultaneously. The results are shown in Table III. It will be observed that there was a reduction in the sucrose clearances, similar in magnitude to that of the creatinine clearances (Table II). (c) Inulin clearances. These were determined on J.T.B. and R.M.L. (simultaneously with the creatinine and urea clearances). 50 g. were given intravenously as a 25 p.c. solution in distilled water containing 3 p.c. of creatinine. The inulin was purified as suggested by W. H. Smith, J. A. Shannon & H. Chasis in a personal communication, and the batch used for J.T.B. was quite non-toxic. A fresh batch was prepared for R.M.L.'s experiment and this subject experienced a slight chilliness and discomfort for about an hour during his preliminary normal experiment. TABLE IV. Inulin clearances during normal health and salt deficiency Normal health clearance dlearance, clearance Clearance, periods c.c./min. periods c.c./min. experi- in each Average and experi. in each Average and Subject ment experiment range ment experiment range J.TAI ( ) ( ) R.M.L ( ) (93-123) ( ) (84-105) The attack began about 60 min. after the inulin had been injected. The inulin was repurified and R.M.L. experienced no reaction following two equally large injections of this inulin when he was salt deficient. He had another mild reaction, however, during the last normal experiment even though the same repurified inulin was used. It is not easy to see why this should have happened but it seems advisable to place it on record although it is not thought to have had any influence upon the kidney function. The results are shown in Table IV, and again indicate a substantial fall of the clearances in both subjects during their periods of salt deficiency.

7 228 R. A. McCANCE AND E. M. WIDDOWSON (6) Clearance ratios With minute volumes of less than 2 c.c./min. the output of urea varies with the minute volume of the urine. The outputs of creatinine, inulin and sucrose do not. Thus clearance ratios involving urea vary with the minute volume when this is below 2 c.c./min. It was therefore originally intended to maintain the urine volumes above 2 c.c./min. throughout all the kidney function tests. This was found to be impossible owing to the difficulty of producing a satisfactory diuresis in several of the subjects. In order therefore to enable direct comparisons to be made of the clearance ratios during the normal and deficient periods attempts were made to carry out normal tests at minute volumes comparable with those produced during salt deficiency. This also proved difficult. Consequently, in order to compare the clearance ratios during the normal and deficient periods it is necessary either to use only the limited number of clearances available over comparable volumes of urine, or to use all the clearance periods after applying the appropriate formula to express the urea clearances as a percentage of "normal". Both alternatives have been tried (see Tables V and VI) and both give essentially the same results. The significant facts which emerge from a study of Table V seem to be: (a) that salt deficiency decreased the urea clearance/creatinine clearance ratio except between minute volumes of 148 and 2*1 in the case of J.T.B. TABLE V. A comparison of the (true) clearance ratios during health and during salt deficiency No. o: cf clearanice Clearance ratios* Range of period1r Subject min. vol. averag( ed U/C U/S Normal health R.B.N D.W. 2* J.T.B. 1* * *32 1 0*326 R.M.L R.B.N * * D.W * J.T.B * R.M.L. 2* * U = urea. C = creatinine. I S = suc rose. U/I C/S C/I * * * I =inulin *38 1* *

8 SALT DEFICIENCY AND URINE SECRETION 229 The validity of this exceptional ratio rests upon the results of a single test period and should possibly be questioned. (b) That salt deficiency decreased the urea clearance/sucrose clearance ratio and the urea clearance/inulin clearance ratio. Again, however, the ratios over J.T.B.'s minute volumes of 1* were exceptional. (c) That salt deficiency did not alter consistently the creatinine clearance/inulin clearance ratio or the creatinine clearance/sucrose clearance ratio. Table VI shows that when the urea clearances are expressed as a percentage of normal, salt deficiency produced in every subject a fall in the ratios urea clearance/creatinine clearance, urea clearance/sucrose TABLE VI. A comparison of all the creatinine, sucrose, inulin and urea clearance ratios. The urea clearances are expressed as a percentage of normal clearance Clearance ratios* periods A Subject averaged U/C U/S U/I C/S C/I Normal health R.B.N D.W J.T.B. 8 0* R.M.L R.B.N D.W J.T.B. 5 0* R.M.L * U = urea. C = creatinine. S = sucrose. I = inulin. clearance and urea clearance/inulin clearance. J.T.B. showed the least change and R.B.N. the greatest. There was no significant change in the creatinine/sucrose or creatinine/inulin clearance ratios. This confirms the results shown in Table V, which were obtained from a much smaller number of clearance periods. DISCUSSION It is probable from the work of Shannon & Smith [1935] and Hendrix et al. [1936] that inulin clearances give a measure of the glomerular filtration rates, and if this is the case, some creatinine is normally excreted by the tubules and some sucrose reabsorbed. Be that as it may, the clearances of all three substances appear to be reduced in exactly the same proportions by salt deficiency. The urea clearance is also reduced by salt deficiency but to a greater extent than the creatinine, inulin, or sucrose clearances. It is difficult to understand why salt deficiency should bring about differential filtration rates in the glomeruli. One must suppose, therefore, that the fall in the clearance

9 230 R. A. McCANCE AND B. M. WIDDOWSON ratios involving urea is due to increased urea reabsorption [Shannon, 1936; Gordon et al. 1937]. In other words Blum et at. [1928, 1929] were, to a limited extent, correct in postulating a reabsorption of urea " par manque de sel ". Why salt deficiency should lead to an increased reabsorption of urea is a matter of pure conjecture since nothing is known about even the normal mechanism. The main cause of the "ureemia", however, would appear to be a reduction in the glomerular filtration rate. The present experiments show that salt deficiency does not reduce the glomerular filtration by causing a fall of arterial blood pressure, since the blood pressure of these subjects did not fall [McCance, 1936b]. The decrease in filtration rates in these experiments, moreover, is not due to a diminished protein intake [Cope, 1933; Pitts, 1935; Shannon et at. 1932; Goldring et at. 1934; Herrin et at. 1937]. It is true that J.T.B. was so nauseated while he was salt deficient that he ate little for 2 days except carbohydrate, but the level of the blood ureas in all the subjects and the fact that they were excreting g. of N daily in the urine shows that their protein metabolism was high. The remaining possibilities seem to be: (a) an increase in the colloidal osmotic pressure of the blood (this certainly occurs in man, but may be unimportant, for in rabbits salt deficiency may lead to a fall in glomerular filtration without any concentration of plasma colloids [Wilkinson, 1937]). (b) A reduction in the number of "active" glomeruli owing to the diminution in blood volume. (c) A diminished circulation rate (caused by increased blood viscosity). (d) Something unknown and possibly unsuspected. It is necessary to make this reservation because of the fluctuations in glomerular filtration rates which seem to occur in beriberi [N a k a z awa & Kusakari, 1930], or uncompensated alkalosis [McC ance & Widdowson, 1937] and possibly following diabetic coma [McCance & Lawrence, 1935], or alkalosis during salt deficiency [McCance & Widdowson, 1936], etc., and for which none of the above explanations suffice. The work of Herrin et al. [1937] suggests that the rise and fall of glomerular filtration rates associated with variations in protein intake may be metabolic in origin. It is not at present clear why the metabolism of certain substances should affect the glomerular filtration rate, but the extension of this conception to the investigation of clinical problems seems to offer interesting possibilities.

10 SALT DEFICIENCY AND URINE SECRETION 231 SUMMARY Severe salt deficiency produced experimentally by diet and sweating in normal men was accompanied by: (a) A rise in the blood urea. (b) No obvious change in the power of the kidney to concentrate urea. (c) A diminution in the power of ingested water to produce a diuresis. (d) A fall in the creatinine, sucrose, inulin and urea clearances. The clearances of the first three fell together and to the same extent. The fall in urea clearance was proportionately greater. It is probable from a consideration of (d) that salt deficiency led to diminished glomerular filtration and also some additional urea reabsorption. The authors are very grateful to the subjects for their co-operation in some rather uncomfortable experiments. One of us (E. M. W.) is indebted to the Medical Research Council for a part-time grant. REFERENCES Baldes, E. J. & Smirk, F. H. (1934). J. Physiol. 82, 62. Blum, L., Grabar, P. & Van Caulaert (1928). Presse m&d. 36, Blum, L., Grabar, P. & Van Caulaert (1929). Ann. Med. 25, 34. Cope, C. L. (1933). J. clin. Invest. 12, 567. Goldring, W., Razinsky, L., Greenblatt, M. & Cohen, S. (1934). Ibid. 13, 743. GoIdring, W. & Smith, H. W. (1936). Proc. Soc. exp. Biol., N.Y., 34, 67. Gordon, W., Alving, A. S., Kretzschmar, N. R. & Alpert, L. (1937). Amer. J. Physiol. 119, 483. Hendrix, J. P., Westfall, B. B. & Richards, A. N. (1936). J. biol. Chem. 116, 735. Herrin, R. C., Rabin, A. & Feinstein, R. N. (1937). Amer. J. Physiol. 119, 87. Kerpel-Fronius, E. (1936). Ergebn. inn. Med. Kinderheilk. 51, 623. McCance, R. A. (1936a). Proc. Roy. Soc. B, 119, 245. McCance, R. A. (1936b). Lancet, 2, 643, 704, 765, 823. McCance, R. A. (1937). Biochem. J. 31, McCance, R. A. & Lawrence, R. D. (1935). Quart. J. Med. 4, 53. McCance, R. A. & Widdowson, E. M. (1936). Proc. Roy. Soc. B, 120, 228. McCance, R. A. & Widdowson, E. M. (1937). Lancet, 1, 247. Nakazawa, F. & Kusakari, H. (1930). Tohoku J. exp. Med. 16, 321. Pitts, R. F. (1935). J. Nutrit. 9, 657. Shannon, J. A. (1936). Amer. J. Physiol. 117, 206. Shannon, J. A., Jolliffe, N. & Smith, H. W. (1932). Ibid. 101, 625. Shannon, J. A. & Smith, H. W. (1935). J. clin. Invest. 14, 393. Wilkinson, B. M. (1937). Unpublished.