THE EFFECTS OF SELECTIVE DEPLETION OF HYDROCHLORIC ACID ON ACID-BASE AND ELECTROLYTE EQUILIBRIUM

Incidence of hypochloremic metabolic alkalosis in dogs and cats with and without nasogastric tubes over a period of up to 36 hours in the intensive care unit

OBJECTIVE

To evaluate the incidence of hypochloremic metabolic alkalosis (HCMA) in dogs and cats in the ICU that had intermittent nasogastric tube (NGT) aspiration for up to 36 hours.

DESIGN

Prospective cohort study (December 2013 to October 2014).

SETTING

Privately owned emergency and referral teaching hospital.

ANIMALS

Forty-nine client-owned dogs and 16 client-owned cats.

INTERVENTIONS

Patients wherein NGT placement was recommended and client consent was obtained were included in the interventional group. Those with an NGT placed (NGT group) had the NGT aspirated every 4 hours. Patients for whom placement of a NGT was declined by the owner served as a reference group (NoNGT). Venous blood gas and electrolyte values were obtained every 12 hours.

MEASUREMENTS AND MAIN RESULTS

Thirty-five dogs and cats had an NGT placed. Thirty dogs and cats did not have an NGT placed. The serum venous blood gas and electrolyte changes were compared over time within the NGT group and between the NGT and NoNGT groups. No cases developed HCMA. In the NGT group, blood pH increased over time. There was no significant difference between the NGT and the NoNGT group in the average value of pH, HCO₃^- , base excess, chloride, or corrected chloride. Serum venous blood gas, chloride, and corrected chloride changes were not associated with the volumes of gastric fluid aspirated over time.

CONCLUSIONS

In this small population of dogs and cats, intermittent NGT aspiration was not associated with the development of HCMA over a period of up to 36 hours after NGT placement.

Exercise-associated hyponatremia in Alaskan sled dogs: urinary and hormonal responses

Exercise-associated hyponatremia occurs in horses and humans, both species that sweat, and in sled dogs, which do not sweat. To investigate the mechanism of exercise-associated hyponatremia in sled dogs, we measured water turnover, serum electrolyte concentrations and osmolality, plasma renal hormone concentrations, and urine composition of 12 fit Alaskan sled dogs before, during, and after a 490-km sled dog race (Ex group). Water turnover and serum electrolyte concentrations were measured in six similarly fit dogs that did not run (Sed group). Water turnover was significantly larger (P < 0.001) in Ex [190 +/- 19 (SD) ml . kg-1 . day-1] than in Sed dogs (51 +/- 13 ml . kg-1 . day-1). There were significant (P < 0.001) decreases in serum sodium concentration (from 148.6 +/- 2.8 to 139.7 +/- 1.9 mmol/l) and osmolality (from 306 +/- 9 to 296 +/- 5 mosmol/kgH2O) of Ex, but not Sed, dogs during the race. Plasma concentrations of arginine vasopressin decreased, whereas aldosterone and plasma renin activity increased significantly (P < 0. 01) during the race. Urine osmolality was unchanged, whereas urine sodium, potassium, and chloride concentrations decreased significantly (P < 0.05) and urine urea concentration increased (P = 0.06). These results demonstrate increased water turnover associated with hyponatremia and renal sodium conservation with maintained high urine osmolality in exercising Alaskan sled dogs.

Application of multivariate autoregressive modelling for analysing chloride/potassium/bicarbonate relationship in the body

The authors repeatedly analysed course data of acid-base disturbances accompanying hypochloraemia and/or hypokalaemia by means of multivariate autoregressive modelling. It was found that the regulatory relationship between chloride and bicarbonate is inverse between the following two hypochloraemic hyperbicarbonataemic states: the one induced by chloride depletion and the other induced by CO2 retention. Also, the study revealed an independent role of potassium deficiency in the development of metabolic alkalosis, especially in cases with mineralocorticoid-induced alkalosis. The present approach enabled the authors to solve a long-standing problem, i.e. to differentiate between the roles of chloride and potassium in the development of metabolic alkalosis.

Chronic neutral phosphate supplementation induces sustained, renal metabolic alkalosis

The aim of the present study was to test whether intravenous neutral phosphate supplementation, recently shown in our laboratory to acutely stimulate proton secretion in the distal nephron, was able to induce a sustained metabolic alkalosis. Neutral Na and K phosphate supplementation for seven days, with equivalent reduction in chloride supply and unchanged intake of sodium and potassium, in ADX rats receiving fixed physiological doses of aldosterone and dexamethasone (group 1, N = 7), was responsible for a severe metabolic alkalosis (MA; delta [HCO3] 11 +/- 1.3 mM, and delta pH 0.11 +/- 0.06 unit). Metabolic alkalosis was at least in part of renal origin, since net acid excretion (NAE) transiently increased, principally due to an increment in titratable acid excretion rate. Balances were equilibrated for sodium and negative for chloride and potassium, which may have contributed to the severity of the MA. Chronic i.v. neutral Na phosphate, without change in potassium and chloride supply, in ADX rats receiving the same doses of steroids (group 2, N = 5), was responsible for a less severe MA (delta [HCO3] 7.5 +/- 0.9 mM, and delta pH 0.07 +/- 0.01 unit), also of renal origin. In this group, balances were positive for chloride and sodium and equilibrated for potassium. Finally, neutral Na and K phosphate supplementation with reduction in chloride supply in intact rats (group 3, N = 4) was also able to induce a MA (delta [HCO3] 5.5 +/- 1.8 mM, and delta pH 0.06 +/- 0.01 unit) of renal origin, with balances negative for chloride and equilibrated for potassium and sodium. In all groups, the generation and maintenance of MA probably resulted from stimulated proton secretion in the distal nephron, as suggested by the observed increase of PCO2 over HCO3 concentration ratio in the urine and a fall in urine pH despite augmented urinary buffer content throughout the phosphate infusion period. Glomerular filtration rate did not significantly vary in any group. In conclusion, chronic supplementation of neutral phosphate appears to stimulate per se proton secretion in the distal nephron, independently of sodium, chloride, and potassium balances, and adrenal steroid secretion. Thus neutral phosphate supplementation should be added to the previously known factors able to induce MA.

Chloride-depletion metabolic alkalosis induces ECF volume depletion via internal fluid shifts in nephrectomized dogs

We recently reported that chloride-depletion metabolic alkalosis (CDMA) results in renal losses of Na, K, and water. In these studies we investigated whether CDMA (induced using a new model that avoids external changes in Na and water balance) was also associated with internal Na and water shifts out of the ECF. CDMA was induced using haemofiltration in functionally nephrectomized dogs. Plasma ultrafiltrate was substituted quantitatively with a solution duplicating each dog's plasma electrolyte composition in control animals, and with a solution containing HCO3 as the sole anion in CDMA animals. ECF volume was estimated as the space of distribution of [3H]-mannitol. Plasma composition and [3H]-mannitol distribution space were unchanged in control dogs. In CDMA dogs metabolic alkalosis developed; despite the absence of external changes in Na and water balance, the space of distribution of [3H]-mannitol decreased by 335 +/- 46 ml (equivalent to 8% of baseline ECF volume), calculated chloride space fell by 304 +/- 50 ml, and haematocrit increased from 45.6 to 48.5 vol%. We conclude that CDMA causes an internal shift of fluid out of the ECF. The resulting ECF volume contraction appears to be an inherent feature of CDMA.

On the mechanism by which chloride corrects metabolic alkalosis in man

To determine whether administration of chloride corrects chloride-depletion metabolic alkalosis (CDA) by correction of plasma volume contraction and restoration of glomerular filtration rate or by an independent effect of chloride repletion, CDA was produced in normal men by the administration of furosemide and maintained by restriction of dietary sodium chloride intake. Negative sodium balance (-112 +/- 16 meq) and reduced plasma volume (2.53 versus 2.93 liters, p less than 0.05) developed. The cumulative chloride deficit of 271 +/- 16 meq was then repleted by oral potassium chloride (267 +/- 19 meq) over 36 hours with continued serial measurements of glomerular filtration rate, effective renal plasma flow, plasma volume, body weight, and plasma renin and aldosterone levels. CDA was corrected, even though body weight, plasma volume, glomerular filtration rate, and renal plasma flow all remained reduced and plasma aldosterone was elevated; urinary bicarbonate excretion increased during correction. Administration of an identical potassium chloride load to similarly sodium-depleted but not chloride-depleted normal subjects produced no change in acid-base status. It is concluded that chloride repletion can correct CDA by a renal mechanism without restoring plasma volume or glomerular filtration rate or by altering sodium avidity.

Renal response to metabolic alkalosis induced by isovolemic hemofiltration in the dog

We describe a new model of chloride-depletion alkalosis (CDMA), in which the method of induction of alkalosis does not itself cause a direct alteration in sodium and fluid balance. We have used this model, which is based on hemofiltration techniques in the dog, to study the immediate response of the kidney to the induction of CDMA. Normal dogs maintained with a NaCl-free diet for several days underwent hemofiltration of 50 ml/kg over a 35 minute period. The hemofiltrate was replaced ml for ml with a solution containing sodium and potassium in the same concentrations as found in each animal's plasma water. In control animals, the replacement solution contained chloride and bicarbonate in the same ratio as in the plasma; in the experimental (CDMA) animals the replacement solution contained bicarbonate as the only anion. In the control group, the procedure of hemofiltration coupled with isovolemic replacement caused no appreciable changes in plasma composition, urinary excretion rates, GFR, or tubular handling of bicarbonate. In the CDMA group, 106 +/- 8.4 mEq of chloride were removed in exchange for bicarbonate. A marked metabolic alkalosis resulted, plasma bicarbonate concentration increasing from 21.9 +/- 0.6 to 33.3 +/- 0.6 mEq/liter. The hemofiltration procedure itself, by design, did not alter sodium or fluid balance. Nevertheless, cumulative urinary sodium excretion increased over 2.5 hours by 23.0 +/- 6.4 mEq. A natriuresis of this magnitude is equivalent to a loss of ECF volume of approximately 200 ml. GFR did not change significantly. The rate of tubular reabsorption of bicarbonate increased significantly from 1209 +/- 82 to 1559 +/- 148 mu Eq/min in CDMA animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-base disturbances in gastrointestinal disease

Gastrointestinal disorders are associated with severe and often complex acid-base disturbances. We review the most important types of metabolic alkalosis and metabolic acidosis associated with gastrointestinal disorders, excluding liver disease. Special emphasis is placed on pathophysiologic mechanisms. This information may help the clinician understand the generation and maintenance of these disorders and to plan an effective therapeutic approach.

Effects of chloride and extracellular fluid volume on bicarbonate reabsorption along the nephron in metabolic alkalosis in the rat. Reassessment of the classical hypothesis of the pathogenesis of metabolic alkalosis

Volume expansion has been considered essential for the correction of chloride-depletion metabolic alkalosis (CDA). To examine the predictions of this hypothesis, rats dialyzed against 0.15 M NaHCO3 to produce CDA and controls, CON, dialyzed against Ringer-HCO3 were infused with either 6% albumin (VE) or 80 mM non-sodium chloride salts (CC) added to 5% dextrose (DX) and studied by micropuncture. CDA was maintained in rats infused with DX. VE expanded plasma volume (25%), maintained glomerular filtration rate (GFR), but did not correct CDA despite increased fractional delivery of total CO2 (tCO2) out of the proximal tubule (36 +/- 2%) as compared with VE/CON (24 +/- 4%; P less than 0.05). In contrast, CC corrected CDA despite volume contraction (-16%) and lower GFR than CC/CON; proximal tCO2 delivery in CC/CDA (29 +/- 4%) did not differ from VE/CDA. CC was associated with an increment in tCO2 excretion. The data strongly suggest that maintenance and correction of CDA are primarily dependent upon total body chloride and its influences on intrarenal mechanisms and not on the demands of sodium or fluid homeostasis.

The regulation of renal acid secretion: new observations from studies of distal nephron segments

In this review we have attempted to present for the general reader the new information on renal acidification that has emerged from the study of discrete segments of the distal nephron. We have structured our presentation in the context of the cation exchange hypothesis which has strongly influenced modern thinking of acid-base regulation. We have shown that distal nephron acidification is active and can proceed even in the absence of sodium. We have also shown beyond doubt, that pH or the determinants of pH can influence the rate of proton secretion in probably all of the distal nephron segments. We have drawn attention to an exciting new means by which chloride (or its substitution) could alter the rate of net bicarbonate transport. A possible role for bicarbonate secretory activity in the mammalian distal nephron has been discussed as has the influence of mineralocorticoids on acid secretion. There is no question that all of this new information has created the need for a reassessment of the validity of the cation exchange hypothesis. After all, this is a view which specifically denies that renal acid excretion is modulated by pH of the blood, and affirms that it is intrarenal sodium handling that is the "driving force", so to speak, behind acidification responses. However, it seems inappropriate at this time to insist that current data do not allow for a component of sodium transport by the distal nephron to modulate the rate of acid secretion. It is also possible, as we have suggested, that an important effect of chloride gradients, independent of blood pH, could alter bicarbonate retrieval. Most importantly, we wish to stress that much of the in vitro perfusion data does not derive from animals subjected to the chronic acid-base derangements which were precisely those situations to which the cation exchange hypothesis was directed. Simply put, the whole animal studies of Schwartz and his colleagues provided no experimental observations on intrarenal sodium handling or acidification mechanisms, just as the microperfusion studies, both in vivo and in vitro, provide insufficient data that can be applied to whole animals subjected to chronic disturbances.(ABSTRACT TRUNCATED AT 400 WORDS)

Segmental chloride and fluid handling during correction of chloride-depletion alkalosis without volume expansion in the rat

To determine whether chloride-depletion metabolic alkalosis (CDA) can be corrected by provision of chloride without volume expansion or intranephronal redistribution of fluid reabsorption, CDA was produced in Sprague-Dawley rats by peritoneal dialysis against 0.15 M NaHCO3; controls (CON) were dialyzed against Ringer's bicarbonate. Animals were infused with isotonic solutions containing the same Cl and total CO2 (tCO2) concentrations as in postdialysis plasma at rates shown to be associated with slight but stable volume contraction. During the subsequent 6 h, serum Cl and tCO2 concentrations remained stable and normal in CON and corrected towards normal in CDA; urinary chloride excretion was less and bicarbonate excretion greater than those in CON during this period. Micropuncture and microinjection studies were performed in the 3rd h after dialysis. Plasma volumes determined by 125I-albumin were not different. Inulin clearance and fractional chloride excretion were lower (P less than 0.05) in CDA. Superficial nephron glomerular filtration rate determined from distal puncture sites was lower (P less than 0.02) in CDA (27.9 +/- 2.3 nl/min) compared with that in CON (37.9 +/- 2.6). Fractional fluid and chloride reabsorption in the proximal convoluted tubule and within the loop segment did not differ. Fractional chloride delivery to the early distal convolution did not differ but that out of this segment was less (P less than 0.01) in group CDA. Urinary recovery of 36Cl injected into the collecting duct segment was lower (P less than 0.01) in CDA (CON 74 +/- 3; CDA 34 +/- 4%). These data show that CDA can be corrected by the provision of chloride without volume expansion or alterations in the intranephronal distribution of fluid reabsorption. Enhanced chloride reabsorption in the collecting duct segment, and possibly in the distal convoluted tubule, contributes importantly to this correction.

Metabolic alkalosis in the rat. Evidence that reduced glomerular filtration rather than enhanced tubular bicarbonate reabsorption is responsible for maintaining the alkalotic state

Maintenance of chronic metabolic alkalosis might occur by a reduction in glomerular filtration rate (GFR) without increased bicarbonate reabsorption or, alternatively, by augmentation of bicarbonate reabsorption with a normal GFR. To differentiate these possibilities, free-flow micropuncture was performed in alkalotic Munich-Wistar rats with a glomerular ultrafiltrate total CO2 concentration of 46.5 +/- 0.9 mM (vs. 27.7 +/- 0.9 mM in controls). Alkalotic animals had a markedly reduced single nephron GFR compared with controls (27.4 +/- 1.5 vs. 51.6 +/- 1.6 nl/min) and consequently unchanged filtered load of bicarbonate. Absolute proximal bicarbonate reabsorption in alkalotic animals was similar to controls (981 +/- 49 vs. 1,081 +/- 57 pmol/min), despite a higher luminal bicarbonate concentration, contracted extracellular volume, and potassium depletion. When single nephron GFR during alkalosis was increased toward normal by isohydric volume expansion or in another group by isotonic bicarbonate loading, absolute proximal bicarbonate reabsorption was not substantially augmented and bicarbonaturia developed. To confirm that a fall in GFR occurs during metabolic alkalosis, additional clearance studies were performed. Awake rats were studied before and after induction of metabolic alkalosis associated with varying amounts of potassium and chloride depletion. In all cases, the rise in blood bicarbonate concentration was inversely proportional to a reduction in GFR; filtered bicarbonate load remained normal. In conclusion, a reduction in GFR is proposed as being critical for maintaining chronic metabolic alkalosis in the rat. Constancy of the filtered bicarbonate load allows normal rates of renal bicarbonate reabsorption to maintain the alkalotic state.

Perimolysis: unveiling the surreptitious vomiter

Perimolysis is a dental condition linked to chronic regurgitation. When perimolysis is found in the patient who denies vomiting, one must suspect anorexia nervosa, a disorder with a high rate of morbidity and mortality. The dental literature has not provided guidelines for confirming the suspicion of surreptitious vomiting. The purpose of this case report is to describe our approach, using simple blood and urine studies, which establishes whether a patient who has perimolysis but denies vomiting is a surreptitious vomiter.

The nature of the renal response to chronic disorders of acid-base equilibrium

The rate of acid excretion by the kidney appears to be determined by factors regulating the site and the rate of sodium reabsorption, rather than by a homeostatic mechanism that responds to systemic pH. This hypothesis, although unconventional, is supported by much experimental evidence, and it accounts for a wide variety of clinical and physiologic findings that heretofore have been difficult or impossible to explain.

Regulation of acid-base equilibrium in chronic hypocapnia. Evidence that the response of the kidney is not geared to the defense of extracellular (H+)

It is generally believed that the reduction in plasma [HCO3] characteristic of chronic hypocapnia results from renal homeostatic mechanisms designed to minimize the alkalemia produced by.the hypocapneic state. To test this hypothesis, we have induced chronic hypocapnia in dogs in which plasma [HCO3] had previously been markedly reduced (from 21 to 15 meq/liter) by the prolonged feeding of HCl. The PaCO2 of chronically acid-fed animals was reduced from 32 to 15 mm Hg by placing the animials in a large environmental chamber containing 9% oxygen. In response to this reduction in PaCO2, mean plasma [HCO3] fell by 8.6 meq/liter, reaching a new steady-state level of 6.4 meq/liter. This decrement in plasma [HCO3] is almost identical to the 8.1 meq/liter decrement previously observed in normal (nonacid-fed) animals in which the same degree of chronic hypocapnia had been induced. Thus, in both normal and HCl-fed animals, the renal response to chronic hypocapnia causes plasma [HCO3] to fall by approximately 0.5 meq/liter for each millimeter of Hg reduction in CO2 tension. By contrast, the response of plasma [H+] in the two groups was markedly different. Instead of the fall in [H+] which is seen during chronic hypocapnia in normal animals, [H+] in HCl-fed animals rose significantly from 53 to 59 neq/liter (pH 7.28-7.23). This seemingly paradoxical response is, of course, an expression of the constraints imposed by the Henderson equation and reflects the fact that the percent fall in [HCO3] in the HCl-fed animals was greater than the percent fall in PaCO2. These findings clearly indicate that in chronic hypocapnia the kidney cannot be regarded as the effector limb in a homeostatic feedback system geared to the defense of systemic acidity.

Renal regulation of acid-base equilibrium during chronic administration of mineral acid

Previous studies in metabolic alkalosis have demonstrated that two factors are the prime determinants of acid excretion and bicarbonate reabsorption; first, the diversion to distal exchange sites of sodium previously reabsorbed in the proximal tubule and loop of Henle; and, second, a stimulus to sodium-cation exchange greater than that produced by a low-salt diet alone. In the present study we have examined the hypothesis that these two factors are also the prime determinants of acid excretion during the administration of mineral acid loads. To test this hypothesis, we have administered to dogs ingesting a low NaCl diet a daily dose of 7 meq/kg of H+ with anions (chloride, sulfate, or nitrate) whose differing degrees of reabsorbability influence the speed and completeness with which each is delivered to the distal nephron with its accompanying Na+. After 2-3 wk of acid administration, and after an initial urinary loss of Na+ and K+, the steady-state value for plasma [HCO3-] was 8.6 meq/liter below control in the HCl group, 3.7 meq/liter below control in the H2SO4 group, and unchanged from control in the HNO3 group; all of these values were significantly different from each other. We would propose the following explanation for our findings: when HCl is administered chronically, marked acidosis occurs because distal delivery of Cl- is restricted by the ease with which the Cl- can be reabsorbed in the proximal portions of the nephron. Only when Cl- retention produces sufficient hyperchloremia to insure delivery of Na+ (previously reabsorbed in proximal tubule and loop of Henle) to the distal nephron in quantities equal to ingested Cl is this primary constraint removed. In the case of sulfuric and nitric acids, there is no constraint on distal delivery, the nonreabsorbability of the administered anion causing prompt, total delivery of Na+ to exchange sites in quantities equal to administered hydrogen. Thus, with H2SO4 and HNO3 the sole constraint on removal of the acid load is the inability of the distal exchange mechanism to conserve the Na+ increment fully by means of H+ exchange. Escape of Na+ and K+ into the urine and the resulting stimulus to Na(+)-H+ exchange remove this constraint and are responsible for establishment of a new steady-state of acid-base equilibrium at plasma [HCO3-] levels significantly higher than those seen with HCl. The feeding of HCl in the presence of a normal salt intake led to a degree of metabolic acidosis not significantly different from that seen in dogs ingesting a low-salt diet. We suggest that the presence of dietary sodium at distal exchange sites did not enhance acid excretion because it is only after a loss of body sodium stores that sodium avidity is increased sufficiently to allow full removal of the acid load. The present findings indicate that the fundamental factors controlling acid excretion and bicarbonate reabsorption in metabolic acidosis are closely similar to those operative in metabolic alkalosis.

Therapy of bicarbonate-losing renal tubular acidosis

A 2-year-old-girl with severe bicarbonate-losing renal tubular acidosis was treated successively with bicarbonate, THAM, and two diuretics, hydrochlorothiazide and frusemide. Only with hydrochlorothiazide was adequate correction of the acid-base balance achieved. The relative importance of changes induced by this treatment in the extracellular fluid volume and in chloride depletion was assessed.

Regulation of renal bicarbonate reabsorption by extracellular volume

The ability of the kidney to reabsorb bicarbonate is held to be a function of plasma CO(2) tension, carbonic anhydrase activity, and potassium stores. The effects of alterations of extracellular volume on bicarbonate reabsorption were studied in dogs whose arterial Pco(2) was kept constant at 40 mm Hg (range 35-45 mm Hg). The effect of extracellular volume expansion was studied in dogs receiving hypertonic bicarbonate and isotonic saline, isotonic saline alone (two of the animals in this group received HCl to lower the plasma bicarbonate concentration), and isotonic bicarbonate. The results were similar in each group. Extracellular volume expansion depressed bicarbonate reabsorption. This depression was related not to changes in glomerular filtration rate (GFR) or bicarbonate concentration, but to the increase of fractional sodium excretion. In addition, volume expansion with bicarbonate increased chloride excretion. Bicarbonate loading was performed in two groups of dogs in which effective expansion of extracellular volume was minimized by hemorrhage or acute constriction of the thoracic vena cava. Both groups demonstrated enhanced bicarbonate reabsorption relative to that seen in the volume-expanded groups. Release of the caval ligature promptly decreased bicarbonate reabsorption. Plasma potassium decreased in all animals studied, but the changes in bicarbonate reabsorption noted could not be related to the decrease. This study demonstrates that the state of effective extracellular volume is a major determinant of bicarbonate reabsorption by the kidney.

Gastric secretion after massive small bowel resection

This paper confirms that gastric hypersecretion can occur in man and dogs after massive intestinal resection. The assumption, made by others, that hypersecretion in the clinical situation is similar to that observed in dogs is challenged. An acute hypersecretory state occurred in eight of 19 patients after massive intestinal resection. This was apparent as an increased rate of basal secretion. It was usually transient and unrelated to the length of intestine resected. A correlation was noticed between hypersecretion and jaundice in the immediate postoperative period. Histamine release after acute hepatic injury was postulated as the cause of the hypersecretion. By contrast a chronic gastric hypersecretory state was demonstrated in dogs after massive intestinal resection. The rate of basal secretion was not significantly altered. The increased daily acid output was shown to be due to prolonged and enhanced response to food. The cause was thought to be loss of inhibitory agents, such as enterogastrone, normally released by the small intestine when in contact with food. The rationale of performing vagotomy and pyloroplasty at the same time as the intestinal resection is questioned.

Correction of metabolic alkalosis by the kidney after isomertric expansion of extracellular fluid

Metabolic alkalosis was induced in dogs by administering ethacrynic acid and sustained by feeding a chloride-deficient diet. At the height of the alkalosis extracellular fluid was expanded "isometrically," i.e., with an infusion that duplicated plasma sodium, chloride, and bicarbonate concentrations. Correction of metabolic alkalosis promptly followed such expansion and was attributed to the selective retention by the kidneys of chloride from the administered solution. Since plasma chloride concentration was not increased as an immediate consequence of the infusion, it is concluded that the change in renal tubular function that led to the selective retention of chloride must have been mediated by factors independent of filtrate chloride concentration.A decrease in circulating mineralocorticoid level, as a consequence of volume expansion, does not seem to account for this change in tubular function since identical studies in dogs receiving excessive amounts of 11-deoxycorticosterone acetate during the day of infusion yielded similar findings. Moreover, no other consequence of volume expansion appears to be sufficient to cause this change in tubular function in the absence of metabolic alkalosis; when the alkalosis was corrected with hydrochloric acid before infusion, isometric expansion of extracellular volume did not induce selective chloride retention. We suggest that isometric expansion during metabolic alkalosis causes a decrease in proximal sodium reabsorption that relinquishes filtrate to a more distal site in the nephron and that this site may retain chloride preferentially when hypochloremia or chloride deficiency is present.

Aldosterone in metabolic alkalosis

Studies have been carried out in human volunteer subjects to evaluate the role of aldosterone in the development, maintenance, and correction of metabolic alkalosis induced by selective depletion of hydrochloric acid. During the first phase of our study the rate of aldosterone secretion was measured before the induction of alkalosis (while the subjects were on a low salt diet) and again after a steady state of metabolic alkalosis had been established. The data demonstrate a fall in aldosterone secretion from a value of approximately 500 mug/day to a value of approximately 200 mug/day. Thus, it appears that an increased rate of aldosterone secretion is not a prerequisite to the elevation of the renal bicarbonate threshold. During the second phase of our study, aldosterone was administered to the alkalotic subjects in doses of 1000 mug/day (or deoxycorticosterone acetate in doses of 40 mg/day) in order to determine the effects of a persistent steroid excess on the ability of sodium chloride to correct the acid-base disturbance. The data demonstrate that despite the administration of steroid, the ingestion of sodium chloride led to a reduction in plasma bicarbonate concentration from 39 to 29 mEq/liter, accompanied by a suppression of renal acid excretion. This reduction in plasma bicarbonate concentration occurred without a concomitant retention of potassium, a deficit of as much as 400-500 mEq of potassium persisting during repair of the acid-base disturbance. Our findings suggest that "saline-resistant" alkalosis, when it occurs in the absence of primary hyperadrenalism, cannot be attributed to aldosterone excess and/or potassium depletion of the magnitude seen in our study. We also suggest the need for a reappraisal of the way in which aldosterone excess contributes to the genesis and maintenance of alkalosis in primary aldosteronism.

The renal response to acid loads in metabolic alkalosis; an assessment of the mechanisms regulating acid excretion

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