Search

Background: The source of glutamine for renal ammonium production is ultimately dietary protein in the fed state and body proteins in fasting. Objective: Our objective was to determine if less NH+4 would be excreted by fasted dogs with chronic metabolic acidosis resulting in conservation of lean body mass. Methods: Acid-loaded fed and fasted dogs were given 10 mmol NH4Cl/kg for 5 days; the fasted group had food withheld on days 4 and 5. Results: The renal production of NH+4 was not significantly different in both acid-loaded groups, yet the rate of NH+4 excretion was significantly lower in the fasted dogs (8 vs. 21 mmol NH+4/mmol creatinine). The urine pH was significantly higher (6.0 versus 5.5) while titratable acid and the urine flow rate were significantly lower in these fasted dogs. Despite nearly equal urine flow rates and Na+ excretion rates after an infusion of saline, the fasted dogs failed to increase the rate of excretion of NH+4 to rates seen in the fed group. Conclusions: The lower rate of excretion of NH+4 in fasted, acidotic dogs appeared to be due to a lower distal H+ secretion. This may help preserve lean body mass during fasting.

Antikaliuretic action of trimethoprim is minimized by raising urine pH. This study was designed to test the hypothesis that the antikaliuresis caused by trimethoprim could be diminished by alkalinizing the luminal fluid in the CCD, thereby converting trimethoprim from its cationic, active form to an electroneutral, inactive form. Timethoprim-induced inhibition of transepithelial Na + transport was examined in A6 distal nephron cells by analysis of short circuit current. The voltage-dependence of the trimethoprim-induced block of Na + channels was examined with patch clamp recordings of A6 cells. The antikaliuretic effect of trimethoprim was examined in vivo in rats pretreated with desoxycorticosterone and with NH 4 Cl to lower urine pH, and in rats also receiving acetazolamide to raise urine pH. We found that the concentration of trimethoprim required to inhibit the amiloride sensitive component of short circuit current by 50% (IC 50 ) was 340 µ m (at pH 8.2) and 50 µ m (at pH 6.3). The IC 50 s of protonated trimethoprim were similar (34 µ m at pH 8.2 and 45 µ m at pH 6.3). The mean time open for the high selectivity, Na + channel was reduced from 1679 ± 387msec to 502 ± 98msec with addition of 10 -5 m trimethoprim to patch pipette solution at the resting membrane potential (-V pipette = 0 mV). Further decreases in mean time open were observed as -V pipette was reduced (that is, apical membrane hyperpolarization) to -40mV (mean time open=217 ± 85 msec) and to -80mV (mean time open=69 ± 13 msec). In vivo , trimethoprim caused a > 50% reduction in potassium (K + ) excretion due primarily to a fall in the [K + ] in the lumen of the terminal CCD. This effect of trimethoprim was markedly attenuated in an alkaline urine induced by acetazolamide. We conclude that it is the charged, protonated species of trimethoprim which blocks epithelial Na + channels. Increasing urinary pH decreases the concentration of the charged species of trimethoprim and minimizes its antikaliuretic effect.

The purpose of this study was to provide a better understanding of the physiological role of endogenous net organic acid production in rats consuming their usual diet. Balance studies were performed over 24 h, and urine was collected in the day and night portions of the diurnal cycle. A supplemented low-electrolyte diet (LED) was fed to determine whether urinary organic anions were identical to those in the diet. A titration procedure was developed to determine the p K of titratable groups in the urine of rats studied with and without an acid load. Although normal rats excreted net acid (NAE), the latter was inversely related to the amount of food consumed. The rates of excretion of bicarbonate ([Formula: see text]), citrate, unmeasured organic anions, and [Formula: see text] were higher in the night portion of the diurnal cycle. NAE rose dramatically when alkali intake was decreased by consuming the LED. Dietary and urinary organic anions were not identical because rats fed the LED supplemented with potassium citrate excreted 4Cl was given intraperitoneally, H+did not appear to be retained, yet NAE rose by only close to 2,000 μeq. The rate of excretion of titratable groups with a p K in the 3 to 5 pH range fell by close to 1,000 μeq; most of these changes occurred in the first 7 h after NH4Cl was given. We conclude that rat chow provides a large net alkali load. There appear to be two types of endogenous acid production, a form associated with a rise in NAE (e.g., sulfuric acid) and dietary alkali-driven endogenous net acid production, which titrates this alkali. Renal excretion of organic anions makes these acids end products of metabolism.

What is the impact of potassium excretion on the intracellular fluid volume: Importance of urine anions. Hyponatremia is a common electrolyte abnormality that causes symptoms as a result of swelling of brain cells. We evaluated the impact of a negative balance for sodium (Na) and potassium (K) salts on the intracellular fluid (ICF) volume, emphasizing the role of anions excreted with K. Rats (N = 10) were deprived of food and water for 24 hours. They received half-isotonic saline to expand their extracellular fluid (ECF) volume by 20%; a long acting antidiuretic hormone (DDAVP) preparation was given to prevent the excretion of electrolyte-free water. The concentration of Na in plasma fell from 139 ± 1mm to 120 ± 2mm 24 hours after the infusion of hypotonic saline (P < 0.01). Since these rats had a small negative balance for water (4 ± 1 ml), hyponatremia was due to their negative balances for Na (2.2 ± 0.3 mmol) and K (2.2 ± 0.1). There were negative balances for Cl (2.4 ± 0.2 mmol) and phosphate (0.7 ± 0.05 mmol). Despite the negative balance for NaCl, the ECF volume as assessed by 3H-inulin space was not contracted. In this model for acute hyponatremia, its basis was electrolyte loss, but the ECF volume was not contracted, suggesting that water shifted from the ICF to the ECF. Hyponatremia is associated with cell swelling only if its cause is positive water balance and/or is loss of Na from the ECF. It is critical to examine the urine anions to determine the compartment of origin of particles excreted with K and thereby whether hyponatremia will result in overall expansion or contraction of the ICF volume.

The goal of this study was to evaluate whether sodium bicarbonate might be a useful form of therapy for hypoxic L-lactic acidosis; our aim was to determine if alkali could extend the time of survival in this setting. Hypoxia was induced in anesthetized, paralyzed, artificially ventilated rats by lowering inspired O2 to 5.5%, an amount sufficient to develop a severe degree of L-lactic acidosis. Measuring arterial blood gases frequently permitted maintenance of a near-constant arterial O2 content. Three groups of hypoxic rats were studied: first, no infusions (n = 10); second, sodium bicarbonate at a rate equal to H+ production in the no-infusion group (n = 12); and third, a control for the Na load in the second group as NaCl (n = 17). Survival was close to twofold longer in the sodium bicarbonate group. Part of this beneficial effect seemed to be increased anaerobic glycolysis, producing ATP along with L-lactic acid. In addition, there was a large decrease in the metabolic demand (consumption of O2) in the 7- to 15-min period in the sodium bicarbonate group. Rats exposed to hypoxia and infused with NaCl for 15 min or alkali for 15, 27, or 40 min were then returned to room air; all survived for the subsequent experimental period of 150 min. We found that there is both a rationale and experimental evidence for giving sodium bicarbonate to prolong survival during hypoxia.

The purpose of this study was to explore the interrelations among energy turnover, the selection of fuels, and the production of ammonium (NH4+) in the kidney during chronic metabolic acidosis. Experiments were carried out in dogs because of the extensive background literature in this species. The specific question addressed was, will a diminished rate of oxidation of fatty acids in the kidney permit the rate of extraction of glutamine and the production of NH4+ to rise? Chronic metabolic acidosis was induced by the ingestion of NH4Cl for 5 days to stimulate the rate of production of NH4+. Insulin was administered to diminish the delivery of fatty acids to the kidney. The concentration of fatty acids in plasma fell from 350 ± 104 to 188 ± 45 μM, yet there was no significant increase in the rates of production of NH4+, consumption of oxygen, or extraction of glutamine after insulin. Notwithstanding, there was a significant rise in the rate of extraction of lactate by the kidney when expressed per 100-mL glomerular filtration rate. Because there was a significant decline in the level of glutamine in plasma (512 ± 76 to 359 ± 42 μM) 1 h after giving insulin, a second series of experiments was carried out. When glutamine was infused after the insulin period, there was no longer a fall in the concentration of this metabolite. Notwithstanding, the rates of extraction of glutamine and production of NH4+ were not higher in the presence of insulin. These data suggest that the rate of oxidation of fatty acids did not limit the rate of oxidation of glutamine in the kidneys of fed dogs with chronic metabolic acidosis. Rather, there was an enhanced oxidation of lactate when the delivery of fatty acids was decreased.Key words: acid–base balance, ammonium, energy turnover, glutamine metabolism, insulin, oxygen consumption.

The purpose of this study was to explore further the relation between the rates of oxygen consumption and ammonium (NH4+) production in the kidney during chronic metabolic acidosis. The experimental model was the dog with chronic metabolic acidosis because of the extensive background literature in this species. Chronic metabolic acidosis was produced by the ingestion of 10 mmol NH4Cl/kg body weight for 5 days. There was a significant increase in the rate of oxygen extraction when hypernatremia was present. Despite this rise in the rate of oxygen consumption, there was no increase in the rate of NH4+ production nor in the rate of glutamine extraction. These data suggest that hypernatremia might prevent a further augmentation in glutamine extraction when the rate of oxygen consumption rises. In addition, a larger proportion of the NH4+ produced was excreted in the urine during hypernatremia. This increase was associated with a rise in the urine flow rate, but not with a fall in urine pH.Key words: Acid–base, ATP, glutamine, energy metabolism, metabolic acidosis, metabolic regulation, net acid excretion, oxygen consumption.

The purpose of these studies was to clarify the basis of the relationship between the urine bicarbonate concentration and the urine minus blood PCO2 difference in alkaline urine (U-B PCO2) and hence shed light on factors that influence hydrogen ion secretion in the collecting duct in vivo. The U-B PCO2 was used to monitor this latter parameter. In dogs with a normal extracellular fluid (ECF) volume, the U-B PCO2 was not primarily influenced by the urine bicarbonate concentration but rather it was related to the rate of sodium excretion. The U-B PCO2 could be abolished by amiloride when the urine bicarbonate concentration was less than 60 mm. At higher urine bicarbonate concentrations, there was a linear correlation between the U-B PCO2 and the urine bicarbonate concentration in normovolemic dogs given amiloride, but the absolute values were lower than they were in normovolemic animals not treated with amiloride. In the dogs with an expanded ECF volume, the U-B PCO2 was lower than it was in the normovolemic animals, and the U-B PCO2 was nor directly related to the urine bicarbonate concentration and not influenced by the rate of sodium excretion. Amiloride had little influence on the U-B PCO2 under these conditions. These results are interpreted to suggest that the magnitude of collecting duct hydrogen ion secretion is determined primarily by the electrical gradient generated by sodium reabsorption in normovolemic dogs and by the intracellular and lumenal hydrogen ion concentrations when the ECF volume is expanded or when active sodium reabsorption is inhibited by amiloride.

Studies on the mechanism whereby acidemia stimulates collecting duct hydrogen ion secretion in vivo. The purpose of these studies was to elucidate the mechanism whereby collecting duct hydrogen ion secretion was augmented by acidemia. The urine minus blood P CO 2 difference in alkaline urine (U-B P CO 2 ) was used to evaluate this parameter. In dogs with a normal ECF volume, the U-B P CO 2 was high, and there was no significant relationship between the U-B P CO 2 factored for the urine bicarbonate concentration and the blood hydrogen ion concentrations unless amiloride, an agent that abolishes the transtubular potential difference, was present. In this latter case, the U-B P CO 2 was a linear function of the urine bicarbonate concentration, and the U-B P CO 2 factored for the urine bicarbonate concentration was directly proportional to the blood hydrogen ion concentration. To extend the pH range considerably, we used lysine to induce bicarbonaturia in dogs with an expanded ECF volume. Amiloride now caused only a small decrease in the U-B P CO 2 at any urine bicarbonate concentration, and furthermore, it did not influence the linear relationship between the U-B P CO 2 factored for the urine bicarbonate concentration and the blood hydrogen ion concentration. These results suggest that acidemia stimulates collecting duct hydrogen ion secretion by a mechanism that appears to be independent of the amiloride-sensitive component of the U-B P CO 2 . We speculate that the mechanism might involve an increased intracellular hydrogen ion concentration during acidemia. Etude du mecanisme par lequel l'acidemie stimule la secretion d'ion hydrogene par le canal collecteur in vivo. Le but de ce travail est d'elucider le mecanisme par lequel la secretion d'ion hydrogene est augmentee par l'acidemie. La difference urine-sang de P CO 2 en urine alcaline (U-B P CO 2 ) a ete utilisee pour evaluer ce parametre. Chez des chiens avec un volume extracellulaire (ECF) normal, la difference U-B P CO 2 est elevee et il n'y a pas de relation significative entre cette difference rapportee a la concentration urinaire de bicarbonate et la concentration sanguine d'ion hydrogene sauf quand de l'amiloride, un agent qui abolit la difference de potentiel transtubulaire, est administre. Dans ce cas la difference U-B P CO 2 est une fonction lineaire de la concentration urinaire de bicarbonate et U-B P CO 2 rapportee a la concentration de bicarbonate urinaire est directement proportionnelle a la concentration sanguine d'ion hydrogene. Afin d'etendre considerablement l'eventail de pH la lysine a ete employee pour determiner une bicarbonaturie chez le chien dont le volume extracellulaire est augmente. Dans cette situation, l'amiloride ne determine qu'une faible diminution de U-B P CO 2 a n'importe quelle concentration urinaire de bicarbonate, et, de plus, il n'influence pas la relation lineaire entre U-B P CO 2 rapportee a la concentration de bicarbonate urinaire et la concentration sanguine d'ion hydrogene. Ces resultats suggerent que l'acidemie stimule la secretion d'ion hydrogene par le canal collecteur par un mecanisme qui parait independant de la composante sensible a l'amiloride de U-B P CO 2 . Nous faisons l'hypothese que ce mecanisme peut impliquer une augmentation de la concentration intracellulaire d'ion hydrogene au cours de l'acidemie.

Large quantities of ammonium and bicarbonate are produced each day from the metabolism of dietary protein. It has recently been proposed that urea synthesis is regulated by the need to remove this large load of bicarbonate. The purpose of these experiments was to test whether the primary function of ureagenesis in vivo is to remove ammonium or bicarbonate. The first series of rats were given a constant acid load as hydrochloric acid or ammonium chloride; individual rats received a constant nitrogen load at a time when their plasma acid-base status ranged from normal (pH 7.4, 28 mM HCO3) to severe metabolic acidosis (pH 6.9, 6 mM HCO3). Urea plus ammonium excretions and the blood urea, glutamine, and ammonium concentrations were monitored with time. Within the constraints of non-steady-state conditions, the rate of urea synthesis was constant and the plasma glutamine and ammonium concentrations also remained constant; thus it appears that the rate of urea synthesis was not primarily regulated by the acid-base status of the animal in vivo over a wide range of plasma ammonium concentrations. In quantitative terms, the vast bulk of the ammonium load was converted to urea over 80 min; only a small quantity of ammonium appeared as circulating glutamine or urinary ammonium. Urea synthesis was proportional to the nitrogen load. A second series of rats received sodium bicarbonate; urea synthesis was not augmented by a bicarbonate load. We conclude from these studies that the need to dispose of excess bicarbonate does not primarily determine the rate of ureagenesis in vivo. The data support the classical view that ureagenesis is controlled by the quantity of ammonium to be removed.

The purpose of these studies was to determine the reasons for the hypokalaemia observed in rabbits studied in our laboratory. The rabbits consumed standard rabbit chow which is rich in potassium and remained in potassium balance. Hypokalaemia was only observed following anaesthesia. A number of additional investigations were undertaken to clarify the mechanisms involved. The hypokalaemia could not be attributed to technical factors, alkalaemia, hyperinsulinaemia or hyperaldosteronism, but seemed to be a function of anaesthesia. This effect of pentobarbitone anaesthesia was not unique to the rabbit, as similar changes also occurred in the anaesthetized dog. The findings reported in this paper have significant implications with respect to the interpretation of plasma potassium concentrations in anaesthetized subjects or animals.

There is a linear relationship between the [Formula: see text] and blood hydrogen ion concentration in normal dogs, but for theoretical reasons to be discussed, we questioned whether this relationship would apply in animals with metabolic acidosis or alkalosis. To study this in more detail, animals were divided into three groups: normal, metabolically acidotic, and metabolically alkalotic. Following anesthesia and bilateral ureteral ligation, dogs were intubated and ventilated to produce acute steady-state [Formula: see text] values corresponding to the range observed during disease states. Changes in the volume and electrolyte composition of the gastrointestinal fluid and urine as well as the concentration and distribution of lactate were evaluated in all experiments. We observed the previously described linear relationship between the [Formula: see text] and blood hydrogen ion concentration in normal dogs, but the slope of the regression line differed significantly from those of dogs with metabolic acidosis and metabolic alkalosis. On the other hand, there was a consistent relationship between the ratio of the [Formula: see text] values, but not the absolute [Formula: see text], and the change in the plasma bicarbonate concentration over a wide range of [Formula: see text] values in all groups of dogs. The chemical basis for these observations will be discussed.

Formation of calcium carbonate or carbamino compounds in a bicarbonate solution should generate hydrogen ions and thereby elevate the [Formula: see text] of that solution. The presence of these substances in rabbit urine was established by demonstrating a significantly lower value for urine total carbon dioxide content measured by microgasometry (number of moles) than with the titration technique (number of equivalents).As there was a significant correlation between the calcium and the carbonate contents in the urine, we surmised that most of the carbonate was in the form of a suspension of calcium carbonate. Direct analysis of precipitates from rabbit bladders confirmed this impression.The formation of calcium carbonate in a solution should raise the [Formula: see text], by the reaction: [Formula: see text] with subsequent dehydration of the H2CO3. In vitro studies demonstrated that the addition of 1 mmol calcium to 1 L of a 200 mM bicarbonate solution raised the [Formula: see text] by approximately 50 mmHg (1 mmHg = 133.322 Pa). However, in vivo measurements of the [Formula: see text] of rabbit urine containing a similar quantity of calcium carbonate revealed that there was no such rise in vivo (urine values = blood values). Therefore, the formation of calcium carbonate should have occurred at an earlier site in the nephron, thereby allowing the [Formula: see text] to diffuse into peritubular capillaries during transit through the nephron.