Effect of chronic metabolic acidosis on ammonia production fromL-glutamine in microdissected rat nephron segments

To evaluate the role of each nephron segment in renal ammoniagenesis, distribution of renal ammoniagenic activity along the nephron in control and acidotic rats was examined. We used our original aerobic incubation system and ammonia produced from glutamine in 7 defined segments of microdissected nephron was measured using the enzymatic cycling method.When ammonia production in the control was compared in each nephron segment, the highest specific activity of ammoniagenesis per mm tubular length and that per g protein were observed in the proximal straight tubule (PST) and the thick ascending limb of Henle's loop, respectively. Chronic metabolic acidosis increased ammonia production per mm tubular length markedly in the proximal convoluted tubule (PCT) (+171%), moderately in the medullary collecting tubule (+123%) and PST (+77%), and slightly in the distal convoluted tubule (+52%), revealing that the highest activity of ammoniagenesis was located in PCT and PST in acidosis.These data indicate that proximal tubules have major roles in renal ammoniagenesis both in the control and in acidosis. From the early observation of glutaminase I isoenzyme distribution along the nephron, our data suggest that not only phosphate-dependent glutaminase but also phosphate-independent glutaminase may have important roles in renal ammoniagenesis.This study was presented in part at 26th Congress of Japanese Society of Nephrology, Kyoto, 1983     

Impaired urinary acidification in the hypothyroid rat

Summary Since abnormalities in the renal handling of sodium and water in both the proximal and distal tubule have been described in primary hypothyroidism, this study was undertaken to examine renal tubular hydrogen secretion in this disorder. Metabolic acidosis was induced in hypothyroid rats (H) and their age matched controls (C) by the administration of an oral ammonium chloride load of 0.15 g/24 h/kg for three days. On day 3 animals were prepared for clearance and acid-base studies, receiving an infusion of Ringer's solution of 0.6 ml/hr/100 g during surgery and the experimental procedure. A 26% decrease in GFR (P<0.005) and a doubling in fractional excretion of sodium (P<0.02) were observed in H rats. The lowest blood pH and average bicarbonate concentration and the excretion of chloride were similar in the two groups, indicating that the acid load was reabsorbed and led to similar degrees of systemic acidification. Urine flow also was comparable in the two groups. Minimal urine pH after NH₄Cl was 6.21±0.06 in H and 5.68±0.09 in C (P<0.001). Ammonium excretion was 28% (P<0.05) lower in H than in C. The defect in urine acidification in H was only partially corrected after 5 days on a low sodium diet and DOCA administration for 2 days. Fractional bicarbonate excretion at normal blood pH and bicarbonate concentration was not different in the two groups. These data indicate that hypothyroid rats have a mild defect in urine acidification and that it is localized predominantly in the distal tubule.     

Renal tubular acidosis in the Silver-Russell syndrome

Several patients with the Silver-Russell syndrome (SRS) attending our Genetics Clinic were diagnosed as having persistent metabolic acidosis. Since this abnormality has not been reported previously in the SRS, we reexamined 33 SRS patients to evaluate the frequency and type of metabolic acidosis, the clinical and laboratory findings, and the growth pattern in SRS patients with and without metabolic acidosis. Among them, 14 had a consistent decrease in HCO levels. Renal studies in acidotic patients showed urine pH of 5.8 and 24 h urine calcium of <2.4 mg/kg/24 h; serum creatinine, excretion of glucose, and aminoacids were normal, as were renal ultrasound and excretory urography findings. These data supported the diagnosis of renal tubular acidosis, probably type II; the patients were treated with oral bicarbonate and acidosis was corrected successfully. Clinical manifestations were similar in acidotic and non-acidotic patients. The nutritional indices at diagnosis and at last evaluation (at least 8 months after diagnosis) were abnormally low in all patients; however, acidotic patients, treated with bicarbonate, showed an improvement of nutritional status particularly in the weight/height index, although the difference between groups after follow-up did not reach statistical significance. We suggest that metabolic acidosis due to renal tubular acidosis, probably type II, may occur in children with the SRS and should be looked for and treated in all patients. © 1995 Wiley-Liss, Inc.     

Acute effects of acidosis on protein and amino acid metabolism in perfused rat liver

Acidosis is frequently associated with protein wasting and derangements in amino acid metabolism. As its effect on protein metabolism is significantly modulated by other abnormal metabolic conditions caused by specific illnesses, it is difficult to separate out the effects on protein metabolism solely due to acidosis. The aim of the present study was to evaluate, using a model of isolated perfused rat liver, the direct response of hepatic tissue to acidosis. We have compared hepatic response to perfusion with a solution of pH 7.2 and 7.4 (controls). Parameters of protein and amino acid metabolism were measured using both recirculation and single-pass technique with 4,5-[3H]leucine, [1-14C]leucine and [1-14C]ketoisocaproate (ketoleucine) as tracers and on the basis of difference of amino acid levels in perfusion solution at the beginning and end of perfusion. In liver perfused with a solution of pH 7.2, we observed higher rates of proteolysis, protein synthesis, amino acid utilization and urea production. Furthermore, the liver perfused with a solution of pH 7.2 released a higher amount of proteins to perfusate than the liver perfused with a solution of pH 7.4. Enhanced decarboxylation of ketoisocaproate in liver perfused by a solution of a lower pH indicates increased catabolism of branched-chain amino acids (leucine, valine and isoleucine), decreased reamination of branched-chain keto acids to corresponding essential amino acids and increased ketogenesis from leucine.     

Saccharin pre‐exposure enhances appetitive flavor learning in pre‐weanling rats

In adult rats, data suggest that consumption of sweet tastes that do not deliver anticipated caloric consequences using high‐intensity, non‐caloric sweeteners, such as saccharin, interferes with learned relations that may contribute to energy balance. The goal of the present study was to assess the development of learning about sweet taste and calories by assessing whether pre‐exposure to saccharin solutions reduces cue competition in pre‐weanling rats. The results demonstrated that rats pre‐exposed to saccharin and then trained with a novel grape flavor paired with a glucose‐sweetened solution consumed more of the novel grape flavor presented alone than rats that had been pre‐exposed to saccharin and given the grape flavor paired with water alone. No differences in intake of the novel grape flavor were observed in groups given pre‐exposure to water or glucose solutions. Thus, by 15 days of age, rats appear to have established an association between sweet tastes and calories, and this association can be weakened by exposure to saccharin. © 2012 Wiley Periodicals,Inc. Dev Psychobiol 54: 818–824, 2012     

Acute but not chronic metabolic acidosis potentiates the acetylcholine-induced reduction in blood pressure: an endothelium-dependent effect

Metabolic acidosis has profound effects on vascular tone. This study investigated the in vivo effects of acute metabolic acidosis (AMA) and chronic metabolic acidosis (CMA) on hemodynamic parameters and endothelial function. CMA was induced by ad libitum intake of 1% NH4Cl for 7 days, and AMA was induced by a 3-h infusion of 6 M NH4Cl (1 mL/kg, diluted 1:10). Phenylephrine (Phe) and acetylcholine (Ach) dose-response curves were performed by venous infusion with simultaneous venous and arterial blood pressure monitoring. Plasma nitrite/nitrate (NOx) was measured by chemiluminescence. The CMA group had a blood pH of 7.15±0.03, which was associated with reduced bicarbonate (13.8±0.98 mmol/L) and no change in the partial pressure of arterial carbon dioxide (PaCO2). The AMA group had a pH of 7.20±0.01, which was associated with decreases in bicarbonate (10.8±0.54 mmol/L) and PaCO2 (47.8±2.54 to 23.2±0.74 mmHg) and accompanied by hyperventilation. Phe or ACh infusion did not affect arterial or venous blood pressure in the CMA group. However, the ACh infusion decreased the arterial blood pressure (ΔBP: -28.0±2.35 mm Hg [AMA] to -4.5±2.89 mmHg [control]) in the AMA group. Plasma NOx was normal after CMA but increased after AMA (25.3±0.88 to 31.3±0.54 μM). These results indicate that AMA, but not CMA, potentiated the Ach-induced decrease in blood pressure and led to an increase in plasma NOx, reinforcing the effect of pH imbalance on vascular tone and blood pressure control.     

Aldosterone secretion during acute respiratory acidosis and NH4CI-induced metabolic acidosis in the goat

Acute respiratory acidosis was induced in goats by inhalation of 6% or 8% CO₂ in air for 30 min. The lower CO₂ concentration caused a significant rise in plasma Cortisol (PC), but had no appreciable influence upon plasma aldosterone (PA), and did not affect the arterial blood pressure (aBP). A more pronounced PC response was observed in association with the inhalation of 8% CO₂, but also here without concomitant increase in PA. However, the aBP became elevated by about 30% during the CO₂ exposure with a simultaneous increase in glomerular filtration rate and a water diuresis, suggesting that the release of arginine vasopressin temporarily became inhibited. It was confirmed that metabolic acidosis induced by duodenal NH₄Cl administration is preceded by a transient rise in PA. Dexamethasone-induced feedback inhibition of the ACTH secretion blocked the PA response, which possibly reflects NH₄ ion stimulation of the ACTH release. The combined results of the CO₂ and NH₄Cl experiments seem to justify the conclusion that increases in PA seen in conjunction with acidosis do not reflect a direct hydrogen ion stimulation of the adrenal glomerulosa cells.     

Hemodynamics and oxygen balance of the rat uterus

Gornyi Vozdukh (Mountain Air) Health Center, Central Research Laboratory, Central Postgraduate Medical Institute, Moscow. (Presented by Academician of the Russian Academy of Medical Sciences I. P. Ashmarin.) Translated from Byulleten Éksperimental'noi Biologii i Meditsiny, Vol. 114, No. 10, pp. 414–416. October, 1992.     

Influence of hypercapnic acidosis and hypoxia on abdominal expiratory nerve activity in the rat

We studied the influence of hypercapnic acidosis and hypoxia on the neural drive to abdominal muscles in anesthetized and decerebrate rats; this information is unavailable despite widespread use of the rat as an experimental model in respiratory physiology and neurobiology. To minimize confounding influences from receptors in the lungs and chest wall, the animals were vagotomized, paralyzed and mechanically ventilated, and electrical activity was recorded from abdominal muscle nerves. In anesthetized and decerebrate rats, both stimuli evoked steady, low amplitude expiratory discharge that persisted throughout the expiratory phase (E-all activity), but was inhibited during inspiration. We also observed late expiratory, high-amplitude bursts (E2 activity) superimposed on this steady activity, but only at the highest levels of respiratory drive. Hypoxia enhanced abdominal motor activity transiently, whereas hypercapnic acidosis caused a sustained increase in activity. Thus, both hypercapnic acidosis and hypoxia activate abdominal muscle motoneurons in the absence of phasic afferent inputs.     

Diet-induced metabolic acidosis and the performance of high intensity exercise in man

Summary The influence of four isolated periods of dietary manipulation upon high intensity exercise capacity was investigated in six healthy male subjects. Subjects consumed their normal (N) diet (45±2% carbohydrate (CHO), 41±3% fat, 14±3% protein) for four days after which they exercised to voluntary exhaustion at a workload equivalent to 100% . Three further four-day periods of dietary manipulation took place; these were assigned in a randomised manner and each was followed by a high intensity exercise test. The dietary treatments were: a low CHO (3±1%), high fat (71±5%), high protein (26±3%) diet (HFHP); a high CHO (73±2%), low fat (12±2%), normal protein (15±1%) diet (HCLF); and a normal CHO (47±3%), low fat (27±2%), high protein (26±2%) diet (LFHP). Acid-base status and blood lactate concentration were measured on arterialised-venous blood at rest prior to dietary manipulation on each day of the different diets, immediately prior to exercise and at 2, 4, 6, 10 and 15 min post-exercise. Other metabolite concentrations were measured in the blood samples obtained prior to dietary manipulation and immediately prior to exercise. Exercise time to exhaustion after the HFHP diet (179±63 s) was shorter when compared with the N (210±65 s; p<0.01) and HCLF (219±69 s; p<0.05) diets. Exercise time after the LFHP diet (188±63 s) was also reduced when compared with the HCLF diet (p<0.05) but not significantly when compared with the N diet. Immediately prior to exercise after the HFHP diet plasma pH, bicarbonate, blood PCO₂ and base excess levels were lower when compared with the N diet (p<0.05, p<0.001, p<0.001, p<0.001 respectively), the HCLF diet (p<0.05, p<0.001, p<0.01, p<0.001 respectively) and the LFHP diet (p<0.05, p<0.01, p<0.05, p<0.001 respectively). Levels of plasma bicarbonate and blood base excess were also lower after the LFHP diet when compared with the N (p<0.05) and HCLF (p<0.01, p<0.001 respectively) diets. Immediately prior to exercise, plasma free fatty acids (FFA; p<0.001, p<0.01, p<0.05), blood 3-hydroxybutyrate (3-OHB; p<0.05, p<0.05, p<0.05) and plasma urea (p<0.001, p<0.001, p<0.05) were all higher after the HFHP diet when compared with the N, the HCLF and the LFHP diets respectively; plasma total protein was higher when compared with the N diet (p<0.05). The results of the present experiment suggest that dietary composition influences acid-base balance by affecting the plasma buffer base and circulating non-volatile weak acids and by doing so may influence the time taken to reach exhaustion during high intensity exercise.     

Role of hyperglycaemia-related acidosis in ischaemic brain damage

Although previous results have shown unequivocally that pre-ischaemic hyperglycaemia aggravates brain damage due to transient ischaemia, several questions have remained unanswered. First, is the effect of hyperglycaemia due to a further fall in intra- and extracellular pH? Second, is aggravation of damage a step function or a continuous function of plasma glucose concentration or of pH? Third, which are the mechanisms responsible for aggravation of damage, notably for the transformation of selective neuronal damage to infarction, for oedema development, and for post-ischaemic seizures? Recent results have provided new information on all of these issues. Thus, normoglycaemic animals with superimposed hypercapnia showed a similar, albeit not identical, aggravation of ischaemic damage, suggesting that acidosis is one major mediator. Furthermore, experiments with graded increase in plasma glucose concentration revealed a threshold effect at values of 10–12 mM , while microelectrode measurements showed a narrow extracellular pH range (6.4–6.5) for post-ischaemic seizure development. These results suggest that aggravation of damage due to excessive acidosis is due to mechanisms with a steep pH dependence. Finally, results are now at hand suggesting that the effect of acidosis is not mediated by a further perturbation of cell calcium metabolism. The more likely mediators are free radicals. Thus, acidosis is known to enhance iron-catalysed production of reactive oxygen species, probably by releasing iron from its bindings to transferrin, ferritin and other proteins.     

心脏硫酸腺嘌呤预处理大鼠心肌微循环及胶原纤维的变化

目的：观察经典缺血预处理及硫酸腺嘌呤预处理大鼠心肌微循环及心肌问质胶原纤维的变化并探讨其意义。方法：大鼠分假手术组(S)、缺血再灌注组(1／R)、经典缺血预处理组(IPC)、硫酸腺嘌呤预处理组(ASP)，通过电镜二维图像立体计量法，测量心肌毛细血管横截面积，并观察问质胶原纤维的变化。结果：S组、IPC组与ASP组心肌毛细血管的横截面积显著大于I／R组。与I／R组相比较，IPC、ASP组心脏胶原纤维明显增加。结论：心脏经典缺血预处理与硫酸腺嘌呤预处理均能明显扩张心肌间质中血管及促进心脏胶原明显增多。4     

Melatonin‐evoked potentiation of the juvenile rat tail artery neurogenic reactivity depends on degree of the change in the reactivity

Aim: Dependence of the melatonin‐evoked potentiation of the rat tail artery neurogenic reactivity on degree of the change in the reactivity was studied. Method: Electrical field stimulation‐evoked contractile response of the juvenile rat tail artery segment under isometric conditions was recorded. 0.1 μm melatonin was administered after the change in the response produced both spontaneously and by acidification (pH 6.6) or alkalinization (pH 7.8) of the solution. Results: During the course of experiment, the contraction force continuously declined, being reduced by 12 ± 5, 24 ± 7 and 32 ± 6% at 20, 70, and 170 min after beginning of experiment, respectively. Melatonin applied at these time points increased the contraction by 20 ± 5, 41 ± 10, and 48 ± 8%, respectively, relative to control. This increase in potentiating effect of melatonin during the course of experiment was not because of sensitization of the segment to the hormone. Acidosis‐induced considerable decline in neurogenic contraction was counteracted by melatonin, while after alkalosis‐induced augmentation in the contraction the hormone was not effective. Melatonin increased the artery response to 0.1 μm noradrenaline. Conclusion: These data suggest that melatonin can restore an attenuated neurogenic reactivity of the juvenile rat tail artery. The effect is more pronounced with further decrease in reactivity and might be due to a change in sensitivity of the post‐junctional membrane to noradrenaline.     

The weanling rat ventromedial syndrome: males get just as fat as females

Weanling female and male Holtzman rats received bilateral electroytic lesions in the ventromedial hypothalamic nucleus (VMN) at the age of 27 and 26 days, respectively. Sham-operated rats served as controls. The animals were maintained on a synthetic diet (4.2 Cal/g) and tap water ad lib, and body weight, Lee (obesity) Index, tail length and food and water intake were recorded weekly for 6 weeks. The only parameters in which a significant sex difference could be demonstrated were body weight gains and water intake which were greater in the male VMN rats. Female and male VMN rats also utilized food energy for fat deposition, body weight and body length change to the same extent. The data also show that in growing animals, body weight is a poor criterion for the accurate assessment of obesity status and true growth.     

Age differences in the acid-base balance and blood clotting system during starvation

The state of the acid-base balance and of the blood clotting system during starvation was studied in young (5–6 months) and old (24–26 months) male rats. The times of maximal changes in the two systems were found to coincide, but in the young animals the acidotic crisis and hypercoagulation developed earlier and were more severe. The old animals were more resistant to starvation and died later than the young rats.Laboratory of Dietary Hygiene, Institute of Gerontology, Academy of Medical Sciences of the USSR, Kiev. (Presented by Academician of the Academy of Medical Sciences of the USSR D. F. Chebotarev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 10, pp. 1189–1191, October, 1976.     

Effect of L-dopa on emotional responses and serotonin metabolism in the rat brain

Experiments on male Wistar rats showed that injection of L-dopa in doses of 100–200 mg/kg causes a parallel increase in the dopamine and homovanillic acid concentrations in the brain, elevation of the 5-hydroxyindoleacetic acid level, and a decrease in the serotonin concentration. Increased emotional reactivity and aggressiveness of the animals was observed at the same time. L-dopa (100 mg/kg) reduced the binding of serotonin formed from tryptophan (100 mg/kg) and accelerated its catabolism in the brain. At the same time, L-dopa abolished the depressant effect of tryptophan on emotional reactivity and aggressiveness. It is suggested that inhibition of the serotoninergic system in the brain is an essential component of the mechanism of strengthening of emotional responses under the influence of L-dopa.Department of Pharmacology, Tartu University. (Presented by Academician of the Academy of Medical Sciences of the USSR S. V. Anichkov). Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 2, pp. 134–137, February, 1976.     

Basis for lactose aversion in the weanling rat

As reported previously, weanling rats will choose to consume more of a liquid diet composed of 12% lactose (low-L) than of an isocaloric liquid diet composed of 47% lactose (high-L) despite the greater sweetness of the latter diet. To investigate the basis for this, saccharin was added to the high-L diet to overwhelm any unpalatable qualities. The results of several choice tests indicate that pups initially prefer the saccharin-sweetened diet. However, if the low-L diet is the alternate choice, the preference shifts to the low-L diet after several days of exposure. This initial preference for the sweetened high-L diet suggests that the high lactose aversion is due to post-ingestive consequences rather than to low palatability of the high-L diet. Furthermore, it appears that the aversion to a high concentration of lactose takes precedence over a preference for the increased sweetness of the high-L diet.     

Intra- and inter-nephron heterogeneity of gluconeogenesis in the rat: effects of chronic metabolic acidosis and potassium depletion

The intra- and inter-nephron heterogeneity of renal gluconeogenesis within rat proximal tubules and the effects of chronic metabolic acidosis and chronic potassium(K)-depletion were studied using isolated proximal tubules of rats by directly measuring glucose synthesized.The gluconeogenic activity from pyruvate and glutamine in control rats was almost limited to within the early proximal tubule (S1: 45.4±5.7 pmol/mm/60 min from pyruvate; 58.0±6.0 from glutamine). Very low, but detectable gluconeogenesis was observed in the middle portion of the proximal tubule (S2:9.9±2.2 from pyruvate; 4.8±1.1 from glutamine). The rate of glucose production in the terminal proximal tubule (S3) was negligible. Furthermore, gluconeogenesis from glutamine of superficial (SF) nephrons was significantly higher than that of juxtamedullary (JM) ones, whereas no difference was seen in gluconeogenesis from pyruvate.In acidotic and K-depleted rats, significant increase could be seen in S1 and S2, but the increase in S3 was not significant. By the serial determination in acidosis, the glucose production from both substrates was found to be the highest at the second 1 mm segment from the glomerulus, and it decreased downward along the proximal tubule. In acidosis, glucose production from both substrates in SF nephrons and that from glutamine in JM ones were elevated significantly compared with the control, but that from pyruvate in JM nephrons did not change.These results suggest that S1 of the SF nephron plays the most important role in gluconeogenesis in the control, whereas S1 of the JM nephron and S2 contribute to gluconeogenesis in acidotic and/or possibly K-depleted rats.