depression, with consequent elevation of alveolar CO2 tension and acidosis,

Transcription

1 81 J. Physiol. (I953) I22, THE FAILURE OF THE KIDNEY TO RESPOND TO RESPIRATORY ACIDOSIS By D. LONGSON AND J. N. MILLS From the Department of Physiology, University of Manchester (Received 2 March 1953) The renal excretion rates of sodium, potassium, chloride and bicarbonate show simultaneous cyclic variations during the twenty-four hours, independently of sleep, food or other external periodicity. The low output of electrolytes at night is associated with an acid urine and a high output of ammonium ions. During the morning a rising output of electrolytes is associated with a more alkaline urine and a falling output of ammonia (Stanbury & Thomson, 1951; Mills & Stanbury, 1952). Phosphate excretion is somewhat out of phase with that of the other electrolytes, falling when they rise in the morning, and rising in the afternoon, as Fiske (1921) also observed, and is associated, unlike excretion of other electrolytes, with cyclic variation in plasma concentration. The morning behaviour of the kidney, an increased output of sodium, potassium, chloride and HCO3 and decreased output of hydrogen ions and phosphate, can easily be simulated by overbreathing (Stanbury & Thomson, 1952). It is therefore tempting to ascribe the nocturnal behaviour of the kidney to respiratory depression, with consequent elevation of alveolar CO2 tension and acidosis, particularly as cyclic diurnal variations of alveolar C02 tension may persist even if the subject does not sleep (Cohen & Dodds, 1924; Mills, 1953). Davies, Haldane & Kennaway (1920) claim that C02 inhalation increases urinary output of ammonia and titratable acid; and Haldane, Wigglesworth & Woodrow (1924) state that phosphate excretion and plasma concentration are likewise increased. Preliminary experiments (Stanbury & Thomson, 1951; Mills & Stanbury, unpublished) on C02 inhalation failed, however, either to confirm these results or to influence the output of sodium or potassium. As this seemed of interest to our understanding both of renal excretory rhythms and of behaviour of the kidney in acidosis, a fuller study has been carried out Ȧ preliminary account has already appeared (Longson & Mills, 1952). PH. CXXII. 6

2 82 D. LONGSON AND J. N. MILLS METHODS Three healthy male subjects, aged 27, 29 and 38, were investigated. The evening before the experiment the subject abstained from excessive salt, and caffeine alkaloids. At about 6.0 or 9.0 a.m. he arrived at the laboratory, and remained seated until the end of the experiment, drinking 100 ml. water hourly and eating light sandwich meals of similar composition at regular times. No tobacco was smoked, nor were caffeine alkaloids consumed. CO2 experiments were performed exactly as controls except that for about 3 hr the subject was in an atmosphere of 5-6j% C02, in a chamber with capacity approximately The atmosphere was mixed with a fan, and aliquots were removed at intervals for analysis. Urine was collected under paraffin on waking, on arrival at the laboratory, and hourly thereafter. Blood samples from an antecubital vein were collected in a well-fitting oiled syringe and transferred to heparinized tubes. The air space was promptly filled with the subject's alveolar air before the tube was stoppered and mixed, to prevent exchange of C00 between plasma and cells before the plasma was separated by centrifugation. Alveolar air was collected hourly or half-hourly, usually by the method of Henderson & Haggard (1925), as adapted by Mills (1953) for continuous infra-red analysis of alveolar air. Analytical methods Chloride: Volhard-Whitehorn (Douglas & Priestley, 1948). Potassium and sodium: flame photometer, external standard. Phosphate: Fiske & Subarrow (1925). Creatinine: Bonsnes & Taussky (1945). Bicarbonate: Van Slyke & Neill (1924). Ammonium: Aeration and titration (Hawk, Oser & Summerson, 1947). Urinary ph: glass and calomel reference electrode. Earlier determinations were made at room temperature, and 0-01 ph unit added for each 1 difference from 370 C; later determinations were made at 370 C. Plasma ph was calculated in a few experiments by the one-point method of Eisenman (1927), using the alveolar as arterial CO2 tension and equilibrating at a tension as near this as possible with a gas-mixture from a cylinder. Small systematic errors enter into the calculation, since the blood collected was venous, and equilibration was performed at room temperature. The fraction of urinary phosphate titratable to ph 7-4 was calculated from the figure pk2 at 38 = Vt',cited by Sendroy & Hastings (1927)., was taken as [Na] +[K] +[NH4]. RESULTS Six experiments were performed on the three subjects when exposed to CO2 (Table 1) and nineteen controls under exactly similar conditions. A further pair of experiments was performed upon subject M in a state of alkalosis induced by taking 40 g NaHCO3 in divided doses, with and without exposure to C02. Not all the urinary constituents discussed were determined in the earlier experiments. Our essential conclusion is negative, that C02 inhalation altered neither acid nor electrolyte excretion. Since this is at complete variance with the conclusions of Davies et al. (1920) and Haldane et al. (1924), a detailed presentation is desirable; it is also an essential preliminary to further exploration of the diurnal excretory rhythms. Of the urinary contributions to acid-base balance, phosphate, ammonium and bicarbonate were determined in one CO2 exposure on each subject. In two, the phosphate output (Fig. 1) remained within normal limits. In one it

3 KIDNEY AND RESPIRATORY ACIDOSIS 83 rose, but the urine was rather more alkaline than usual, so that the calculated output of dihydrogen phosphate was about the same as in controls; and the phosphate output fell again sharply while the subject was still in the chamber. TABLE 1. Summary of experiments on exposure to C02 Alveolar CO2 tension (mm Hg) During Subject Initial exposure Periods of exposure B Ll Ml MA* * Subject alkalotic through ingestion of NaHC03. E,, 40_, i20 0 HO is Time (hr) Fig. 1. Above: NH4 output, range of 3 controls, and 1 expt. in C02 on each subject. Middle: phosphate output, range of 7 controls, and 1 expt. in COs on each subject. Below: bicarbonate output, subject B, 1 control and 1 expt. in C00. Discontinuous lines represent period in C02. Outputs plotted at mid-point of collection period except for initial level, which represents mean night output. Plasma phosphate was also determined in these three experiments, and was never raised by the exposure to CO2 as Haldane et al. (1924) claimed. In the upper pair of curves of Fig. 2 are plotted the plasma phosphate concentrations 6-2

4 84 D. LONGSON AND J. N. MILLS of subject B, who on exposure to C02 showed a high peak of phosphate excretion; the most that can be said is that the fall of plasma level is less steep than in controls. The curves on subject M (middle group to Fig. 2) follow a similar course whether or not C02 was inspired. The lower curves of Fig. 2 show that the ingestion of sodium bicarbonate reduced the plasma phosphate far below 4) E v 4) -o c vc E (4 Time (hr) Fig. 2. Plasma inorganic phosphate concentration. Above: subject B. Middle: subject M. Below: subject M, taking NaHCO3. 0-0O, control expts. *--- *, expts. with exposure to CO2 during period indicated. the level found in controls, and that the further inhalation of C02, which exactly neutralized the alkalaemia (Fig. 5), had no effect at all upon the hypophosphataemia. The phosphate excretion was also reduced by bicarbonate ingestion below the lower limit of controls, and was unaffected by CO2 inhalation (Fig. 5). The ammonium outputs in CO2, shown in Fig. 1, are unaltered by CO2 inhalation. The bicarbonate output, almost zero during the night, rose in the

5 KIDNEY AND RESPIRATORY ACIDOSIS 85 morning in control experiments at a time characteristic for each subject to between 5 and 40,uequiv/min, and fell to near zero again usually between and The experiments of Fig. 1 show a rise just as large when the subject breathed C02, despite the elevation of alveolar C02 tension from 41 to 53 mm Hg. Other subjects behaved similarly. Time (hr) Fig. 3. Outputs of K+ and H+, and alveolar C02 tension (* ) in control expts. (left) and during exposure to C02 (right). Subjects M, above; L, middle; B, below. The most informative indication of acid excretion by the kidney is probably output of ammonia plus phosphate titratable to ph 7-4, minus bicarbonate (modified from Albright & Reifenstein, 1948), and in Fig. 3 this is plotted with the potassium output, since the competition between potassium and hydrogen ions for exchange with sodium in the renal tubules (Berliner, Kennedy

6 86 D. LONGSON AND J. N. MILLS & Orloff, 1951) may connect the diurnal rhythm in excretion of acid and electrolytes (Mills & Stanbury, unpublished). It will be seen that CO2 inhalation has neither raised the acid output nor depressed the potassium output. Dietary alkalosis (Fig. 4) did however reduce the acid excretion to a large negative value, consisting largely of bicarbonate, since little ammonium or dihydrogen phosphate was excreted in these experiments. Inversely with the acid output, the output of sodium and potassium was very high. The correction of the alkalaemia by C02 (Fig. 5), however, neither depressed these high 1250 NaHCO, 10g taken c u Na 1000 o 500 I 'o (U vp18 10 HCO ~ 0 \~~~~~0 200 a.~~~~~1 -~~~~~~~~~~~~~~0 40I- Sodum poasu n hoieotushvebe eemndi lxei Fig.t4. ments, Subec andec non M,nNaHCO hasc, evern taken bee byemuth dpouhuressedry Urinrese y 002.ut The Tesdu output sodiumc ofnwaso n K.00 outputwas mcmoevralincontrol exp.. experimen, 1C2 0 xp.oup xt upurets potedat pothdan mid-point was-pthatof coletionpeiodėxep poetasspeium. Inep Forinitialeplevel, whihrepretentsmean ofevent forig.i6iare the plottedthihrepoutputs morning rise ngthout eput. ns in CO2. fromngthosetepermnsutrintalyi.h trin alyih morning.o moutputsgo soince Soiumeansowdpoassunoremokthndifid Masowdpoaslater peak thandifid theonthernsubecs inthensubecs alauia. hlauis rhesut Thesut kideyaplotdsparentely.respondedto sodiu bicarbonatehing 2estion,y whcfaisedt ardeyaplotdsparantely.reitowillbe seenu thcatrbreathing02entirelyfhcaiedt preventhae mlorning rise intut s rodim toexetion. t satigealih

7 KIDNEY AND RESPIRATORY ACIDOSIS 87 oo 40. s E o C 0o Z._A <: a I i 7:50 c 30 [_ X 20F _ f- 10o 0 L Fig. 5. Subject M. NaHCO3 taken by mouth. Alveolar CO2 tension, plasma ph and urinary output of phosphate. * -*, control expt.; , CO2 expt. Outputs plotted at midpoint of collection period except for initial level, which represents mean night output. I 100 's 300- CL 0~ 41: V z 100i - Subject M n 2 U Time (hr) Fig. 6. Sodium outputs, early morning expts. only. Above: subjects B and L, range of 3 controls, and 2 expts. in C02. Below: subject M, range of 3 controls, and 2 expts. in C02. Discontinuous lines represent period in C02. Outputs plotted at mid-point of collection period except for initial level, which represents mean night output.

8 88 D. LONGSON AND J. N. MILLS Chloride output followed a course much like that of sodium and at a very similar level, except in the experiments when sodium bicarbonate was ingested. In these the chloride output rose and fell much as in controls, although the sodium output rose to far higher levels. There was no indication that the high output of bicarbonate depressed the chloride output, although since the flows were large the chloride concentration fell. The hourly ingestion of 100 ml. water produced in control experiments a diuresis rather irregular in both timing and magnitude, but usually disappearing in the afternoon. A similar but larger diuresis occurred in all except one exposure to C02, reaching on one occasion a peak flow of 7-2 ml./min. We never observed a fall in flow comparable with nocturnal oliguria. The output of urinary solutes did not appear to be affected by these irregularities of flow; for a steady trend of solute output was often associated with erratic variations of flow, as in the example in Table 2. TABLE 2. Erratic variations in urine flow associated with steady trend in potassium output. Subject L Flow K conen. K output Time (ml./min) (m.equiv/l.) (,uequiv/min) The output of endogenous creatinine was measured in most experiments, since Brod & Sirota (1948) claim that it is proportional to glomerular filtration rate. This output was remarkably constant and never affected by 002. Occasionally, however, when the urine flow was very low and incomplete micturition might significantly affect results, an exceptionally low creatinine output was followed by an unduly high one. It is quite probable that such findings were due to incomplete micturition, and the two consecutive urine samples were therefore pooled for further calculations. DISCUSSION It is well known that the kidney responds to a dietary or metabolic acidosis by an increased acid output, and the claim of Davies et al. (1920) that it responded similarly to a respiratory acidosis seemed so reasonable that it appears to have escaped critical examination. The two experiments these authors describe were however performed at a time of day when acid excretion commonly increases as part of the habitual diurnal rhythm, and no control experiments were recorded. The acid and ammonia outputs recorded as ml. 041 N acid/hr have only to be multiplied by 1-67 to convert them to our units of,equiv/min, when it will be seen that the supposed increase in acid and ammonia output

9 KIDNEY AND RESPIRATORY ACIDOSIS 89 is actually less than we have often observed in controls with no CO2 inhalation. The percentage of C02 breathed was much the same as in our experiments, but the tension attained in alveolar air is not recorded. The phosphate figures of Haldane et al. (1924) need more careful consideration. These authors were aware of the diurnal phosphate rhythm, though it is not clear whether the control figures they cite in the 'discussion' are personal observations upon the same subject, or are taken from the literature. They exposed their subject to C02 at a time of day when phosphate excretion might be expected to increase spontaneously, and when in control experiments we have observed quite sharp rises in plasma phosphate concentration. Admittedly we have never in controls observed so large a rise in excretion; our plasma figures are not strictly comparable, as Haldane et al. determined whole blood inorganic phosphate, but the observations of these authors would be much more convincing if published with control observations on the same subject at the same time of day. In addition, no figures of urinary acidity were published so there is nothing to indicate that any increase in phosphate output aided in the correction of plasma acidity. Our exposures to C02 were much earlier in the day, at a time when plasma phosphate and phosphate output habitually fall; the fall in excretion rate was only once reversed, the fall in plasma level never; and on the one occasion when excretion rate rose, the urine became more alkaline, so that the total acid output still fell; in this experiment phosphate excretion also fell abruptly during continued exposure to C02. The high blood inorganic phosphate and phosphate excretion during nocturnal sleep, recorded by Haldane et al. as evidence of the effect of high alveolar C02 upon blood and urinary phosphate, are probably irrelevant. We (Longson, Mills & Stanbury, unpublished) have observed just as large swings of plasma level and excretion rate during sleepless nights when changes in alveolar C02 tension were minimal. Haldane et al. admit that any effect of C02 upon phosphate excretion is due, mainly at any rate, to a change in plasma level; there is no satisfactory evidence that, either by an effect of its own or by altering the plasma acidity, C02 directly affects the kidney's handling of phosphate. When sodium bicarbonate was taken, the morning fall in phosphate output was rather more profound and prolonged than in controls. Fiske (1921) with 5-10 g sodium bicarbonate, failed to observe any such change, but Haldane et al., with doses similar to ours, mention 'an undecided tendency for the morning fall in the phosphate output to be more profound and the rise delayed longer than under normal conditions'. When we prevented alkalaemia by breathing C02, the renal response was the same; it cannot therefore have been directly due to the change in plasma ph. The plasma phosphate concentration likewise was depressed by bicarbonate ingestion more profoundly than in any controls; Haldane et at., determining whole blood inorganic phosphate, failed

10 90 D. LONGSON AND J. N. MILLS to observe such a change. Again, this profound depression was quite unmodified by a concentration of inspired C02 which completely prevented any change in plasma ph, thus demonstrating the apparent indifference to blood ph per se of another mechanism often supposed to participate in acid-base regulation. Perhaps the most striking instance of the indifference of the kidney to respiratory acidosis is the large matutinal rise of bicarbonate excretion, seen in Fig. 1, occurring whilst the subject was in the C02 chamber, which actually exceeded if it differed at all from the rise in a control experiment. The excretion of sodium and potassium was as completely unaffected as was the acid output by respiratory acidosis. Barbour, Bull, Evans, Hughes Jones & Logothetopoulos (1953) likewise find that breathing 5-7% C02 does not affect sodium nor potassium output, but as their experiments were performed in the afternoon, when outputs are relatively low, they are not strictly comparable. Some uncertainty exists in the literature upon the magnitude of the rise in alveolar C02 tension during nocturnal sleep, estimates ranging from about 2 mm Hg or less (Bass & Herr, 1922; Harrison, King, Calhoun & Harrison, 1934; Magnussen, 1944) to as much as 10 mm (Endres, 1922). We have attained or exceeded the highest of these estimates, without in any way reducing the output of sodium and potassium or urine flow towards the nocturnal low level; and in unpublished experiments we have seen the habitual rhythm persisting during sleepless nights when rises of alveolar C02 tension were around the lower values cited for sleep. It may be that very high levels of blood C02 tension will increase the kidney's output of acid, and perhaps depress the potassium excretion. Singer, Clark, Barker & Elkington (unpublished) make such a claim for subjects spending 30 min in 7 % C02 after sodium bicarbonate ingestion, but their results were very inconsistent, and they always produced a large diuresis, which is very different from the condition during normal sleep. More prolonged exposure to high blood tensions of C02, such as may occur in emphysema, again might affect the kidney in a way not revealed by 3 hr exposures. We have deliberately confined our attention to changes not too far different from those which may occur during sleep. We do not wish in this paper to discuss either the connexion between acidbase balance and output of electrolytes by the kidney, nor the immediate cause of either. Competition between hydrogen and potassium for ionic exchange with sodium in the renal tubules (Berliner et al. 1951) is a possibility quite in accordance with the data of Figs. 3 and 4, which will be discussed in a later paper. It is clear, however, from the present data that the familiar nocturnal aciduria with low electrolyte output cannot be due simply to respiratory depression and consequent elevation of blood 002 tension.

11 KIDNEY AND RESPIRATORY ACIDOSIS 91 SUMMARY 1. Three subjects were exposed for 2-3 hr to 5-61% CO2 at a time in the morning when, in control experiments, outputs of sodium, potassium and bicarbonate were rising, and phosphate, acid and ammonium falling. 2. All these morning tides in excretion rates, except that of phosphate, continued exactly as in controls. 3. In one experiment only, phosphate output rose, but as the urine became more alkaline the total acid excretion fell as in controls. 4. Plasma phosphate concentration fell, as in controls. 5. In a subject in a state of dietary alkalosis, restoration of the plasma ph to normal by C02 inhalation in no way diminished the high sodium, potassium and bicarbonate output, nor raised the low plasma phosphate concentration and phosphate excretion. 6. The kidney did not, over 3 hr, correct a respiratory acidosis; nor can respiratory acidosis be the cause of the habitual behaviour of the kidney at night. Our thanks are due to F.B.B. for acting as subject; and one of us (J.N.M.) is indebted to the Medical Research Council for an Apparatus Grant. REFERENCES ALBRIGHT, F. & REIFENSTEIN, E. C. (1948). The Parathyroid Glands and Metabolic Bone Disease, p London: Baillibre, Tindail and Cox. BARBOuR, A., BuLL, G. M., EVANS, B. M., HUGHIES JONES, N. C. & LOGOTHETOPOULOS, J. (1953). The effect of breathing 5 to 7% carbon dioxide on urine flow and mineral excretion. Clin. Sci. 12, BASS, E. & HERR, K. (1922). Untersuchungen uber die Erregbarkeit des Atemzentrums im Schlaf (gemessen an der Alveolarspannung der Kohlensaure). Z. Biol. 75, BERLINER, R. W., KENNEDY, T. J. & ORLOFF, J. (1951). Relationship between acidification of the urine and potassium metabolism. Amer. J. Med. 11, BONSNES, R. W. & TAUSSKY, H. H. (1945). On the colorimetric determination of creatinine by the Jaffe reaction. J. biol. Cbhem. 158, BROD, J. & SIROTA, J. H. (1948). The renal clearance of endogenous 'creatinine' in man. J. clin. Invest. 27, COHEN, I. & DODDS, E. C. (1924). Twenty-four hour observations on the metabolism of normal and starving subjects. J. Physiol. 59, DAVIEs, H. W., HALDANE, J. B. S. & KENNAWAY, E. L. (1920). Experiments on the regulation of the blood's alkalinity. J. Physiol. 54, DoUGLAS, C. G. & PRIESTLEY, J. G. (1948). Human Physiology, p Oxford: Clarendon Press. EISENMAN, A. J. (1927). A gasometric method for the determination of ph in blood. J. biol. Chem. 71, ENDRES, G. (1922). tber Gesetzmassigkeiten in der Beziehung zwischen der wahren Harnreaktion und der alveolaren C02-Spannung. Biochem. Z. 132, FISKE, C. H. (1921). Inorganic phosphate and acid excretion in the postabsorptive period. J. biol. Chem. 49, FISKE, C. H. & SUBARROW, Y. (1925). The colorimetric determination of phosphorus. J. biol. Chem. 66, HALDANE, J. B. S., WIGGLESWORTH, V. B. & WOODROW, C. E. (1924). The effect of reaction changes on human inorganic metabolism. Proc. Roy. Soc. B, 96, 1-14.

12 92 D. LONGSON AND J. N. MILLS HARRIsON, T. R., KING, C. E., CAUHouN, J. A. & HARRISON, W. C. (1934). Congestive heart failure. Cheyne-Stokes respiration as the cause of paroxysmal dyspnoea at the onset of sleep. Arch. intern. Med. 53, HAWK, P. B., OSER, B. L. & SUMMERSON, W. H. (1947). Practical Physiological Chemistry, 12 ed. p London: Churchill. HENDERSON, Y. & HAGGARD, H. W. (1925). The circulation and its measurement. Amer J. Physiol. 73, LoNGsoN, D. & MILLS, J. N. (1952). Excess carbon dioxide and morning urine. J. Physiol. 118, 6P. MAGNUSSEN, G. (1944). Studies on the Respiration during Sleep, pp London: H. K. Lewis and Co. MTuTs, J. N. (1953). Changes in alveolar carbon dioxide tension by night and during sleep. J. Physiol. 122, MiLs, J. N. & STANBURY, S. W. (1952). Persistent 24-hour renal excretory rhythm on a 12-hour cycle of activity. J. Physiol. 117, SENDROY, J. & HASTINGS, A. B. (1927). The solubility of tertiary calcium phosphate in salt solutions and biological fluids. J. biol. Chem. 71, 788. STANBU-RY, S. W. & THOMSON, A. E. (1951). Diurnal variations in electrolyte excretion. Clin. Sci. 10, STANBURY, S. W. & THOmSON, A. E. (1952). The renal response to respiratory alkalosis. Olin. Sci. 11, VAN SLYKE, D. D. & NEIL, J. M. (1924). The determination of gases in blood and other solutions by vacuum extraction and manometric measurement. J. biol. Chem. 61,