Behavior of various enzyme activities during high blood lactate and pyruvate levels in albino rats reared in a normobaric hypoxic atmosphere for 1 or 2 generations

Albino rats Wistar family raised in normobaric hypoxic environment (10% O2 in N2) since one or two generations showed an increase in arterial blood creatine-kinase, glutamate-dehydrogenase, lactic-dehydrogenase, lactate and pyruvate when compared with normoxic controls. Moreover the values found in hypoxic rats of second generation were intermediate between those found in hypoxic rats of first generation and normoxic controls. These differences are probably due to an improved efficiency of the processes of cellular adaptation to the hypoxic environment when named species remain in hypoxic environment for more than one generation.     

Arterial LDH, 2,3-DPG, lactate, pyruvate and acid-base balance in hypoxic albino rats of first or second generation

Arterial acid-base balance, lactate, pyruvate, lactate dehydrogenase activity (LDH), 2,3-diphosphoglycerate content (2,3-DPG) of normoxic control rats were compared with those of rats exposed to a hypoxic normobaric environment (10% O2 in N2) within a few hours after birth (hypoxic animals of first generation or H1), and with those of rats of second generation (H2) conceived and born in the above mentioned hypoxic environment of H1 parents and maintained always in the same place since their utilization. The H1 rats showed a displacement of acid-base balance towards acidosis and an increase of lactate, pyruvate, LDH and 2,3-DPG in comparison with normoxic controls. The H2 rats showed a significant attenuation of acidosis in comparison with H1 rats; the values of lactate, pyruvate, LDH and 2,3-DPG were intermediate between those found in H1 and normoxic control rats. We believe that these results are in relation with the evolution of adaptative processes to hypoxic environment in hypoxic animals of second generation.     

Acid-base balance and lactatemia in acute hypoxia in normoxic or hypoxic albino rats

Albino rats Wistar family were raised since birth in normobaric hypoxic environment (10% O2 in N2). This hypoxic animal group and a normoxic control group were subjected to acute hypoxia in two spaced tests. The rats were exposed for 15 minutes to 7% O2 and later to 5% O2 gas mixture. At the end of the test with 7% O2 the hypoxic animals since birth showed a smaller quantity of blood lactate and their acid-base balance was more acid when compared to control animals. These differences were significant. In the considered metabolic parameters the differences between the 2 groups became not significant at the end of the test with 5% O2. We believe that the found differences in mentioned parameters between hypoxic and normoxic animals, also according to cellular adaptative processes, occurred during the rearing in hypoxic environment. In the test with 5% O2 the seriousness of the hypoxia overcomes the effects of adaptative mechanisms in hypoxic animals since birth. We believe that hypoxic rats since birth represent, limitedly to some aspects, different metabolic models compared to normoxic animals.     

Metabolic effects of propionate in normal and vitamin B12-deficient rats

1. Administration of propionate caused a twofold increase in the concentrations of lactate and pyruvate in the blood of vitamin B(12)-deficient rats, whereas there was a slight decrease in lactate and a 50% increase in pyruvate in normal rats. 2. Concentrations of total ketone bodies in the blood of normal rats were not significantly altered by propionate administration but the [3-hydroxybutyrate]/[acetoacetate] ratio decreased from 3.0 to 2.0. In the vitamin B(12)-deficient rats there was a 40% decrease in total ketone bodies and a change in the ratio from 3.4 to 1.2. 3. The changes in the concentration of ketone bodies in freeze-clamped liver preparations were similar in pattern to those observed in blood. 4. Propionate administration caused a decrease in the concentration of acetyl-CoA in the livers of both groups of animals, but the absolute decrease was greater in the vitamin B(12)-deficient group. The decrease in the concentration of CoA was similar in both groups. 5. As in blood, there were threefold increases in the concentrations of lactate and pyruvate in the livers of the vitamin B(12)-deficient rats after propionate administration, whereas there was no significant change in the concentrations of these metabolites in the normal rats. 6. There was a 50% inhibition of glucose synthesis in perfused livers from vitamin B(12)-deficient rats when lactate and propionate were substrates as compared with lactate alone. 7. It is concluded that the conversion of lactate into glucose is inhibited in vitamin B(12)-deficient rats after propionate administration, and that this effect is due to inhibition of the pyruvate carboxylase step resulting from a decrease in acetyl-CoA concentration and a postulated increase in methylmalonyl-CoA concentration.     

P50 values in hypoxic albino rats of first and second generation.

We determined the "in vivo" (arterial pH and PCO2) and standard (pH = 7.4, PCO2 = 40 mm Hg) PO2 at 50% O2 saturation of hemoglobin (P50, vv and P50, st) in Wistar albino rats when living in a normobaric hypoxic environment. Two generations of hypoxic rats were observed for changes in their P50, vv, P50, st, (n50) 2,3-diphosphoglycerate (2,3-DPG), hemoglobin (Hb) and DPG-Hb ratio: the first generation (H1) and the second generation (H2). A few hours after birth, the H1 rats were placed and raised in a normobaric hypoxic environment (10% O2 in N2). The H2 rats were born from hypoxic parents of first generation and were raised in the same hypoxic environment. The control group had a normoxic environment. The P50, st was significantly higher in H1 rats than both H2 and controls. P50, st was similar in H2 and control rats. The P50, vv was significantly higher in H1 rats than both H2 and controls but it was significantly lower in H2 when compared with both controls and H1. Hb and 2,3-DPG had values significantly greater for both H1 and H2 when compared with their controls. However, the values of H2 were significantly lower than H1. The effectiveness of an increase in Hb-O2 affinity as an adaptive mechanism in H2 rats is discussed.     

The development of gluconeogenesis in rat liver. Experiments in vivo

1. The injection of substrate amounts of lactate into newborn rats produced an increase in the concentration of phosphoenolpyruvate in liver. Similar experiments with foetal rats showed no increase in phosphoenolpyruvate concentration although pyruvate formation was observed. 2. The administration of pyruvate to foetal rats was also without effect on the hepatic phosphoenolpyruvate concentration, although a 20-fold increase in this was observed when pyruvate was injected into newborn animals. 3. Analogous experiments with aspartate produced qualitatively similar differences between foetal and newborn rats. 4. When [(14)C]-lactate, -pyruvate or -aspartate was injected into foetal or newborn rats incorporation of radioactivity into liver glucose was observed only in the newborn animals. 5. Lactate/pyruvate ratios of 213 in foetal liver and 13.5 in the livers of newborn rats indicated a relatively reduced environment in the cytosol of foetal liver. This difference in redox state was illustrated experimentally by a greater conversion of pyruvate into lactate and an increased formation of malate in foetal liver. 6. Although both the substrate-loading and tracer experiments indicated a block in gluconeogenesis in foetal liver at the stage of conversion of oxaloacetate into phosphoenolpyruvate, gluconeogenesis was also hindered by a highly reduced environment.     

Influence of Perfusate Glucose Concentration on Dialysate Lactate, Pyruvate, Aspartate, and Glutamate Levels Under Basal and Hypoxic Conditions: A Microdialysis Study in Rat Brain

Abstract: The aim of this study was to evaluate the influence of perfusion media with different glucose concentrations on dialysate levels of lactate, pyruvate, aspartate (Asp), and glutamate (Glu) under basal and hypoxic conditions in rat brain neocortex. Intracerebral microdialysis was performed with the rat under general anesthesia using bilateral probes (o.d. 0.3 mm; membrane length, 2 mm) perfused with artificial CSF containing 0.0 and 3.0 m M glucose, respectively. Basal dialysate levels were obtained 2 h after probe implantation in artificially ventilated animals. Dialysate levels of glucose were also measured for the two different perfusion fluids. The mean absolute extracellular concentration of glucose was estimated by a modification of the no-net-flux method to be 3.3 mmol/L, corresponding to an average in vivo recovery of 6% for glucose. Hypoxia was induced by lowering the inspired oxygen concentration to 3%. Hypoxia caused a disturbance of cortical electrical activity, evidenced by slower frequency and lower amplitudes on the electroencephalogram compared with prehypoxic conditions. This was associated with significant elevations of lactate, Asp, and Glu levels. There were no statistically significant differences in dialysate metabolite levels between the two perfusion fluids, during either normal or hypoxic conditions. We conclude that microdialysis with glucose-free perfusion fluid does not drain brain extracellular glucose in anesthetized rats to the extent that the dialysate lactate, pyruvate, Asp, and Glu levels during basal or hypoxic conditions are altered.     

高原低氧胁迫对小鼠肝脏功能及基因表达的影响

低氧作为青藏高原最为特殊的环境因素之一,对高原动物的适应进化产生了深刻的影响。持续的低氧暴露会损伤肝脏功能,引起动物机体代谢紊乱,但连续低氧处理对子代肝脏的影响仍缺乏相关研究。本研究将成年小鼠转移至高原低氧环境(海拔3 220 m)饲养并繁殖,以常氧条件下饲养小鼠为对照,统计低氧处理小鼠(低氧第0代)及其子代(低氧第1～5代)生长数据,发现长期低氧暴露导致小鼠肝脏比重增加,肝细胞肿胀,肝索间红细胞浸润,并且子一代小鼠肝小叶出现脂肪变性。血液生化指标显示,相比于对照组(常氧第0代),低氧第0代和低氧第1代的谷丙转氨酶和谷草转氨酶水平显著上升(P <0.05);血清白蛋白、球蛋白、总胆红素和总胆固醇水平在低氧第0代中下降,低氧第1代中上升(P <0.05)。空腹注射葡萄糖和胰岛素后低氧组小鼠的葡萄糖耐受能力和胰岛素敏感性显著减弱(P <0.05)。常氧第0代、低氧第0代及低氧第1代肝脏RNA-seq分析发现,低氧第0代和低氧第1代共有的459个差异基因显著富集在MAPK、细胞凋亡、脂质代谢和内质网等信号通路。本研究发现低氧胁迫对子代小鼠肝脏具有重要影响,此结果对肝脏低氧生...     

The role of the cytoplasmic redox potential in the control of fatty acid synthesis from glucose, pyruvate and lactate in white adipose tissue

The metabolism of lactate, pyruvate and glucose was studied in epididymal adipose tissue of starved, normally fed and starved-re-fed rats. Lactate conversion into fatty acid occurred at an appreciable rate only in the adipocyte of starved-re-fed animals. NNN'N'-Tetramethyl-p-phenylenediamine, an agent that transports reducing power from the cytoplasm to the mitochondria, caused large increments of fatty acid synthesis from lactate and a smaller one from glucose but a decrease in that from pyruvate. Glucose (1.0mm) increased fatty acid synthesis from lactate 4.3-fold but only 1.67-fold from pyruvate in adipocytes from normally fed animals. 2-Deoxyglucose decreased fatty acid synthesis from lactate to a greater degree (threefold) compared to that from pyruvate in adipocytes from starved-re-fed animals. l-Glycerol 3-phosphate contents were approximately equal in epididymal fat-pads, incubated in the presence of lactate or pyruvate, from normally fed animals, whereas the addition of 1mm-glucose resulted in a tenfold increase in l-glycerol 3-phosphate content only in the presence of lactate. The l-glycerol 3-phosphate content was tenfold higher in adipose tissue from starved-re-fed animals incubated in the presence of lactate than in the presence of pyruvate. 2-Deoxyglucose caused these values to be slightly lowered in the presence of lactate. We suggest that lactate metabolism is limited by the rate of NADH removal from the cytoplasm. In the starved-re-fed state, this occurs by reduction of dihydroxyacetone phosphate formed from glycogen to produce l-glycerol 3-phosphate, thus permitting lactate conversion into fatty acid. When glucose is the substrate, and rates of transport are not limiting, the rate of removal of cytoplasmic NADH limits glucose conversion into fatty acid.     

Response of blood vessels in vitro to hyperbaric oxygen (HBO): Modulation of VEGF and NOx release by external lactate or arginine

Hyperbaric oxygen therapy (HBO) is suggested to promote angiogenesis during wound healing, but the mechanisms involved are not understood. This study used a novel isolated blood vessel preparation to explore the effects of air, normobaric oxygen or hyperbaric oxygen (2.2 ATA for 90 min) on the angiogenesis factor, vascular endothelial growth factor (VEGF), nitrite and nitrate (NO_x), lactate dehydrogenase (LDH) and lactate release from the tissue in normal Krebs Ringer, and the Ringer supplemented with either l-arginine, or 15 mM lactate to mimic a wound environment, or both (l-arginine + lactate). The in vitro blood vessel preparation remained viable during all experiments. There were no effects of HBO treatment on any of the parameters measured in normal Krebs Ringer, but some treatment-dependent effects were observed in supplemented Krebs Ringer. In the lactate supplemented Krebs Ringer, medium LDH levels increased in response to either normobaric oxygen (NBO) or HBO, compared to air alone. There were also small, but statistically significant increases in total glutathione due to HBO treatment, compared to NBO or air in the lactate supplemented medium, and in the combined supplement. There were no effects of HBO on NO_x, changes in external medium lactate levels, or tissue VEGF in any of the Krebs Ringers tested. However, post treatment increases in VEGF were observed in the lactate supplemented medium, and for lactate release into the medium for the combined supplement. We conclude that HBO does not cause NO or VEGF production from the blood vessel in normal Krebs Ringer, but the data from supplemented medium show that the response of the tissue is subtly affected by the chemical environment around the blood vessel, and the tissue is more responsive to HBO when wound conditions are mimicked.     

Metabolic interactions of dichloroacetate and insulin in experimental diabetic ketoacidosis.

1. The infusion of sodium dichloroacetate into rats with severe diabetic ketoacidosis over 4h caused a 2mM decrease in blood glucose, and small falls in blood lactate and pyruvate concentrations. Similar findings had been reported in normal rats (Blackshear et al., 1974). In contrast there was a marked decrease in blood ketone-body concentration in the diabetic ketoacidotic rats after dichloroacetate treatment. 2. The infusion of insulin alone rapidly decreased blood glucose and ketone bodies, but caused an increase in blood lactate and pyruvate. 3. Dichloroacetate did not affect the response to insulin of blood glucose and ketone bodies, but abolished the increase of lactate and pyruvate seen after insulin infusion. 4. Neither insulin nor dichloroacetate stimulated glucose disappearance after functional hepatectomy, but both agents decreased the accumulation in blood of lactate, pyruvate and alanine. 5. Dichloroacetate inhibited 3-hydroxybutyrate uptake by the extra-splachnic tissues; insulin reversed this effect. Ketone-body production must have decreased, as hepatic ketone-body content was unchanged by dicholoracetate yet blood concentrations decreased. 6. It was concluded that: (a) dichloroacetate had qualitatively similar effects on glucose metabolism in severely ketotic rats to those observed in non-diabetic starved animals; (b) insulin and dichloroacetate both separately and together, decreased the net release of lactate, pyruvate and alanine from the extra-splachnic tissues, possibly through a similar mechanism; (c) insulin reversed the inhibition of 3-hydroxybutyrate uptake caused by dichloroacetate; (d) dichloroacetate inhibited ketone-body production in severe ketoacidosis.     

Effect of artificial hibernation state on intensity of metabolic processes in rabbits

Metabolic processes were investigated in the rabbit organism when modeling a condition of hibernation. It is established that during hibernation respiratory subcompensated acidosis develops in animals; the content of lactate and glutamate rises in their blood; activity of lactate dehydrogenase, malate dehydrogenase and isocytrate dehydrogenase increases in the liver cytosol of rabbits, while activity of pyruvate carboxylase and aldehyde dehydrogenase is reduced.     

Increased blood ammonia in hypoxia during exercise in humans

The effect of acute hypoxia on blood concentration of ammonia ([NH3]b) and lactate (la-]b) was studied during incremental exercise(IE), and two-step constant workload exercises (CE). Fourteen endurance-trained subjects performed incremental exercise on a cycle ergometer under normoxic (21% O2) and hypoxic (10.4% O2) conditions. Eight endurance-trained subjects performed two-step constant workload exercise at sea level and at a simulated altitude of 5000 m (hypobaric chamber, P(B)=405 Torr; P(O2)=85 Torr) in random order. In normoxia, the first step lasted 25 minutes at an intensity of 85 % of the individual ventilatory anaerobic threshold (AT(vent), ind) at sea level. This reduced workload was followed by a second step of 5 minutes at 115% of their AT(vent), ind. This test was repeated into a hypobaric chamber, at a simulated altitude of 5,000 m. The first step in hypoxia was at an intensity of 65 % of AT(vent), ind., whereas workload for the second step at simulated altitude was the same as that of the first workload in normoxia (85 % of AT(vent), ind). During IE, [NH3]b and [la-]b were significantly higher in hypoxia than in normoxia. Increases in these metabolites were highly correlated in each condition. The onset of [NH3]b and [la-]b accumulation occurred at different exercise intensity in normoxia (181W for lactate and 222W for ammonia) and hypoxia (100W for lactate and 140W for ammonia). In both conditions, during CE, [NH3]b showed a significant increase during each of the two steps, whereas [la-]b increased to a steady-state in the initial step, followed by a sharp increase above 4 mM x L(-1) during the second. Although exercise intensity was much lower in hypoxia than in normoxia, [NH3]b was always higher at simulated altitude. Thus, for the same workload, [NH3]b in hypoxia was significantly higher (p<0.05) than in normoxia. Our data suggest that there is a close relationship between [NH3]b and [la-]b in normoxia and hypoxia during graded intensity exercises. The accumulation of ammonia in blood is independent of that of lactate during constant intense exercise. Hypoxia increases the concentration of ammonia in blood during exercise.     

Comparison of glucose metabolism in the lactating mammary gland of the rat in vivo and in vitro. Effects of starvation, prolactin or insulin deficiency

1. Measurements of arteriovenous differences across mammary glands of normal and starved lactating rats, and lactating rats made short-term insulin-deficient with streptozotocin or prolactin-deficient with bromocryptine, showed that only in the starved animals was there a significant decrease in glucose uptake. This decrease was accompanied by release of lactate and pyruvate from the gland, in contrast with the uptake of these metabolites by glands of normal lactating rats. 2. There were no marked differences in metabolite concentrations in freeze-clamped glands in the four conditions studied, apart from a decrease in [lactate] and [pyruvate] and an increase in [glucose] in the glands of the streptozotocin-treated group. 3. Acini isolated from the glands of starved, insulin or prolactin-deficient rats had a higher production of lactate and pyruvate from glucose than did glands from normal rats; this is in agreement with the reported decrease in the proportion of active pyruvate dehydrogenase in these situations [Field & Coore (1976) Biochem. J.156, 333-337; Kankel & Reinauer (1976) Diabetologia12, 149-154]. 4. Addition of insulin did not increase the uptake of glucose by acini from normal glands, but it caused a significant increase in the utilization of glucose by acini from glands of starved rats. Insulin did not decrease the accumulation of lactate and pyruvate in any of the experiments. 5. It is concluded that isolated acini represent a suitable model for the study of mammary-gland carbohydrate metabolism in that they reflect metabolism of the gland in vivo.     

The effect of energy substrate concentration and amino acids on the in vitro development of preimplantation porcine embryos

As the pig becomes increasingly used for biomedical research, an effective and efficient in vitro culture system is essential. This study aimed to improve the commonly used porcine embryo culture medium, NCSU23, by altering the energy substrates and adding amino acids, using electrically activated diploid parthenotes from oocytes obtained from the ovaries of prepubertal and adult animals. Morphological development to day 6 and blastocyst cell number were examined. Glucose (5.56 mM) was replaced by pyruvate and lactate (0.2 mM and 5.7 mM, respectively) for either the entire culture period or for the first 48 h only. Blastocyst rates were not different between any of the treatments, and were similar for prepubertal and adult oocytes. When the embryos were cultured with pyruvate and lactate for the first 48 h and then glucose, there was a significant increase in blastocyst cell number compared to glucose only. Blastocysts produced using pyruvate and lactate for the entire time tended to have more cells than those exposed to glucose only and less than those who were cultured in pyruvate and lactate for the first 48 h and then glucose. Nonessential amino acids added for the first 48 h and nonessential and essential amino acids added for the remaining time significantly increased blastocyst cell number only when the embryos were grown in pyruvate and lactate followed by glucose. Blastocyst rates were not different between any of the treatments, and this result was the same when using sow or gilt oocytes. The modified medium was then tested using in vitro matured and fertilized embryos from sow oocytes. Blastocyst rates and cell number were significantly increased in the modified medium compared to those grown in unmodified NCSU23. This shows that altering energy substrates and adding amino acids can increase the quantity and cell number of IVP blastocysts compared with NCSU23.     

Plasmodium berghei: lactic acidosis and hypoglycaemia in a rodent model of severe malaria; effects of glucose, quinine, and dichloroacetate

Fulminant malaria infections are characterised by hypoglycaemia and potentially lethal lactic acidosis. In young adult Wistar rats (n = 26) infected with Plasmodium berghei (ANKA strain), hyperparasitaemia (greater than 50%), anaemia (PCV 19.6 +/- 5.3%; mean +/- SD) hypoglycaemia (1.04 +/- 0.74 mmol/litre), hyperlactataemia (13.2 +/- 2.20 mmol/litre), hyperpyruvicaemia (0.51 +/- 0.12 mmol/litre) and metabolic acidosis (arterial pH 6.96 +/- 0.11) developed after approximately 14 days of infection. Hypoglycaemia was associated with appropriate suppression of plasma insulin concentrations. In a second series of experiments the metabolic effects of treatment with glucose (500 mg/kg/hr), quinine (5 mg/kg bolus followed by 10 mg/kg over 1 hr) and a potent activator of pyruvate dehydrogenase, dichloroacetate (300 mg/kg) were studied over a 1-hr period. In control animals quinine had no measurable effects, but dichloroacetate significantly reduced arterial blood lactate (74%) and pyruvate (80%). In infected animals, glucose infusion attenuated the rise in lactate (38% compared with 82%; P less than 0.01) but quinine had no additional metabolic effects. Dichloroacetate further attenuated the rise in lactate (14%; P less than 0.01).     

The metabolic effects of sodium dichloroacetate in the starved rat

1. Sodium dichloroacetate (300mg/kg body wt. per h) was infused in 24h-starved rats for 4h. 2. Blood glucose decreased significantly, an effect that had previously only been noted in diabetic animals 3. Plasma insulin concentration decreased by 63%; blood lactate and pyruvate concentrations decreased by 50 and 33%, whereas concentrations of 3-hydroxybutyrate and acetoacetate increased by 81 and 73% respectively. 4. Livers were freeze-clamped at the end of the 4h infusion. There were significant decreases in hepatic [glucose], [glucose 6-phosphate], [2-phosphoglycerate], the [lactate]/[pyruvate] ratio, [citrate] and [malate], and also [alanine], [glutamate] and [glutamine], suggesting a diminished supply of gluconeogenic substrates. 5. Animals subjected to a functional hepatectomy at the end of 2h infusions showed no difference in blood-glucose disappearance but a highly significant decrease in the rate of accumulation of lactate, pyruvate, glycerol and alanine, compared with control animals. Dichloroacetate decreased ketone-body clearance. 6. After functional hepatectomy an increase in glutamine accumulation appeared to compensate for the decrease in alanine accumulation. 7. It is concluded that dichloroacetate causes hypoglycaemia by decreasing the net release of gluconeogenic precursors from extrahepatic tissues while inhibiting peripheral ketone-body uptake. 8. These findings are consistent with the activation of pyruvate dehydrogenase (EC 1.2.4.1) in rat muscle by dichloroacetate previously described by Whitehouse & Randle (1973).     

Effects of acute hypoxia and hyperoxia on respiratory rate in albino rats chronically exposed to hypoxia

Changes in respiratory frequencies with hypoxic or hyperoxic exposure were studied in: 12 normoxic control rats (N) born and raised in normoxic environment at sea level; 12 rats (A) born and raised in normoxic environment at sea level exposed to normobaric hypoxia (10% O2 in N2) as adults; 12 rats of first generation (G1) raised in the above mentioned hypoxic environment since a few hours after birth; 12 rats of third generation (G3) conceived and born in the hypoxic environment of hypoxic parents of second generation and maintained continuously under hypoxic conditions until their utilization. The response of A rats to 10% O2 and 7% O2 breathing was elevated (57% and 86% over air breathing). The mean respiratory frequency of A rats exposed to 7% O2 rose to a greater extent than did that of N rats. The G1 and G3 rats were less responsive to 7% O2 (64% and 37% over air breathing, respectively) than N and A rats; however, in G1 rats the exposure to 7% O2 produced a greater rise of frequency than in G3 rats. Furthermore A rats, G1 rats and G3 rats were less responsive to 97% O2 breathing (19%, 19% and 11% below air breathing, respectively). Comparing these data with previous findings we suggest that, with chronic exposure to hypoxia, changes in ventilatory response to hypoxia and hyperoxia occur in the following manner: I) loss of response to hypoxia if chronic exposure is begun in the immediate postnatal period; 2) degree of response to hypoxia or hyperoxia influenced by duration of chronic exposure.     

Profound hypoglycemia in starved, ghrelin-deficient mice is caused by decreased gluconeogenesis and reversed by lactate or fatty acids

When mice are subjected to 7-day calorie restriction (40% of normal food intake), body fat disappears, but blood glucose is maintained as long as the animals produce ghrelin, an octanoylated peptide that stimulates growth hormone secretion. Mice can be rendered ghrelin-deficient by knock-out of the gene encoding either ghrelin O-acyltransferase, which attaches the required octanoate, or ghrelin itself. Calorie-restricted, fat-depleted ghrelin O-acyltransferase or ghrelin knock-out mice fail to show the normal increase in growth hormone and become profoundly hypoglycemic when fasted for 18-23 h. Glucose production in Goat(-/-) mice was reduced by 60% when compared with similarly treated WT mice. Plasma lactate and pyruvate were also low. Injection of lactate, pyruvate, alanine, or a fatty acid restored blood glucose in Goat(-/-) mice. Thus, when body fat is reduced by calorie restriction, ghrelin stimulates growth hormone secretion, which allows maintenance of glucose production, even when food intake is eliminated. In humans with anorexia nervosa or kwashiorkor, ghrelin and growth hormone are known to be elevated, just as they are in fat-depleted mice. We suggest that these two hormones prolong survival in starved humans as they do in mice.     

Regulation of Alternative Oxidase Activity by Pyruvate in Soybean Mitochondria

The regulation of alternative oxidase activity by the effector pyruvate was investigated in soybean (Glycine max L.) mitochondria using developmental changes in roots and cotyledons to vary the respiratory capacity of the mitochondria. Rates of cyanide-insensitive oxygen uptake by soybean root mitochondria declined with seedling age. Immunologically detectable protein levels increased slightly with age, and mitochondria from younger, more active roots had less of the protein in the reduced form. Addition of pyruvate stimulated cyanide-insensitive respiration in root mitochondria, up to the same rate, regardless of seedling age. This stimulation was reversed rapidly upon removal of pyruvate, either by pelleting mitochondria (with succinate as substrate) or by adding lactate dehydrogenase with NADH as substrate. In mitochondria from cotyledons of the same seedlings, cyanide-insensitive NADH oxidation was less dependent on added pyruvate, partly due to intramitochondrial generation of pyruvate from endogenous substrates. Cyanide-insensitive oxygen uptake with succinate as substrate was greater than that with NADH, in both root and cotyledon mitochondria, but this difference became much less when an increase in external pH was used to inhibit intramitochondrial pyruvate production via malic enzyme. Malic enzyme activity in root mitochondria declined with seedling age. The results indicate that the activity of the alternative oxidase in soybean mitochondria is very dependent on the presence of pyruvate: differences in the generation of intramitochondrial pyruvate can explain differences in alternative oxidase activity between tissues and substrates, and some of the changes that occur during seedling development.