Liver Phosphoenolpyruvate Carboxykinase Activity Research Articles

Effects of nutritional history on stress response in gibel carp (Carassius auratus gibelio) and largemouth bass (Micropterus salmoides).

The stress response of omnivorous gibel carp (Carassius auratus gibelio) and carnivorous largemouth bass (Micropterus salmoides) with different nutritional history were evaluated. A 2×2 layout, including two fish species (gibel carp or largemouth bass) and two nutritional history (fasted or fed to satiation for four weeks), was used. After feeding or fasting, the fishes were subjected to an acute handling. Fasting resulted in decrease of plasma glucose level and liver glycogen content of gibel carp and largemouth bass. After handling stress, plasma levels of cortisol, glucose and lactate of gibel carp and largemouth bass increased, regardless the fasted fish or fed fish. During the period from 0h to 24h post-stress, the fasted gibel carp exhibited lower plasma cortisol and glucose levels, brain and liver glycogen contents, and liver phosphoenolpyruvate carboxykinase (PEPCK) activity compared with the fed counterpart. The plasma glucose level, brain glucose level, brain and liver glycogen contents were lower, while the liver PEPCK and hexokinase (HK) activities were higher, in the faster largemouth bass than the fed counterpart. This study indicates that nutritional history can influence stress response of gibel carp and largemouth bass, and the stress response is less severe in the fasted fish relative to the fed counterpart. This study also reveals that gibel carp and largemouth bass may have different strategies in response to fasting and acute handling stress.

Cytokines (IL-1β and TNFα) in relation to biochemical and immunological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats

Previous studies in different strains of rats and mice have shown that the inhibition of gluconeogenesis as a result of reduced liver phosphoenolpyruvate carboxykinase (PEPCK) activity together with appetite suppression play critical roles in the acute toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Recent immunological studies in rats demonstrated that exposure to low doses of TCDD resulted in an early and enhanced IgG response to immunization with sheep red blood cells (SRBC) and an enhanced delayed-type hypersensitivity (DTH) reaction as well as a positive popliteal lymph node (PLN) response. However, high doses of TCDD suppressed the DTH reaction. This study aimed at examining the involvement of cytokines (IL-1 and TNF) in mediating the above effects. Liver samples from a previous dose-response study on DTH reaction were investigated, in which rats were treated with TCDD (1, 3, 10, 30 and 90 μg/kg) and immunized with an antigen. mRNA levels of IL-1β were elevated begining at the 1 μg/kg (non-lethal) dosage group with a maximum increase of about 5-fold above controls in the 90 μg/kg (lethal) dosage group. mRNA levels of TNFα were also significantly elevated begining at the 30 μg/kg dosage group. These results suggest that at low doses of TCDD, increased IL-1β could be responsible for immune function stimulation, whereas at high doses of TCDD, greatly elevated TNFα and IL-1β levies may exacerbate or mediate acute toxicity including immune suppression and related biochemical effects. A time course study (60 μg TCDD/kg without immunization) revealed that liver mRNA levels of TNFα were significantly elevated starting 24 h, and reaching a maximum 48 h after dosing with TCDD. This change was accompanied by a transient increase of mRNA levels of IL-1β at day 4 after TCDD dosage. Thus, these data demonstrated that TCDD alone (without immunization) can cause transient increases of mRNA levels of TNFα and IL-1β in liver. Results from these experiments suggest that TCDD-induced cytokine changes may play important roles in various effects of TCDD.

Glycerol synthesis in the rainbow smelt Osmerus mordax

Rainbow smelt, Osmerus mordax, maintain high glycerol levels in winter to avoid freezing. After intramuscular injection of 14C-labeled glucose, [14C]glycerol was found in the blood, liver and muscle, indicating that glycogen is a source of glycerol. Levels of both the active and inactive forms of glycogen phosphorylase were higher in muscle in winter than in autumn, although the fraction in the active form did not change significantly. More of the phosphorylase was in the active form in the liver than in the muscle. Short-term starvation resulted in a significant decrease in the level of glycogen soon after the stomachs were emptied, presumably to replace glycerol lost to the water. However, tissue glycerol levels remained relatively high, despite a near depletion of glycogen reserves. Triglyceride levels increased slightly during starvation, indicating that triglycerides were not involved in glycerol synthesis. After intramuscular injection of 14C-labeled pyruvate, [14C]glycerol was found in the blood, liver and muscle, indicating a second route, presumably from muscle protein, to glycerol synthesis. Liver phosphoenolpyruvate carboxykinase activity was slightly higher in winter, possibly to assist in the conversion of pyruvate to glycerol.

Involvement of liver and skeletal muscle in sucrose-induced insulin resistance: dose-response studies.

The ability of dietary sucrose to induce insulin resistance independent of changes in body weight is controversial. In the present study male rats were fed a high-starch (ST) diet (starch 68% of total kcal) ad libitum for 2 wk and then were fed equicalorically either the ST diet or a high-sucrose (SU) diet (sucrose 68% of total kcal) for 8 wk. Euglycemic, hyperinsulinemic (0, 1.2, 4.1, 8, 15 mU.kg-1.min-1, n = 6-8/group per dose) clamps were then used to establish dose-response relationships for glucose kinetics and metabolism. Body weight (513 +/- 3 g) and composition were similar between groups after the 8-wk dietary period. Glucose infusion rates (GIR; mg.kg-1.min-1) were significantly less in SU (0.9 +/- 5.8 +/- 0.6, 14.8 +/- 1.3, and 18 +/- 1.1) than in ST rats (4.1 +/- 0.9, 12.3 +/- 1.2, 22.6 +/- 1.5, and 25.9 +/- 1.8) at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Impaired suppression of endogenous glucose production accounted for 46, 43, 23, and 0% of the reduction in GIR in SU rats at 1.2, 4.1, 8, and 15 mU.kg-1.min-1, respectively. Despite basal hyperinsulinemia (38 +/- 2 microU/ml in SU vs. 26 +/- 2 microU/ml in ST rats), liver phosphoenolpyruvate carboxykinase (PEPCK) activity was 50% higher in SU than in ST rats and remained elevated in SU rats (by 30-40%) at the two lower insulin doses. No skeletal muscle glycogen accumulation occurred in SU rats at any of the insulin doses, and glycogen synthase I activity was significantly lower in SU rats at the two highest insulin doses.(ABSTRACT TRUNCATED AT 250 WORDS)

The acinar heterotopy of phosphoenolpyruvate carboxykinase activity in rat liver under the influence of the oestrous cycle

The acinar localization of phosphoenolpyruvate carboxykinase was investigated in livers from untreated female rats during the 4-day oestrous cycle. The results were correlated with plasma levels of insulin, glucagon and oestrogens. Total activity was highest in dioestrus and lowest in metoestrus. The highest activities were present in the periportal zone and decreased continuously towards the perivenous zone in all four phases of the cycle. This general pattern was modified under the influence of the cycle. The periportal-perivenous gradient was subject to cycle dependent changes, being steepest in proestrus. In addition to oestrogens the concentrations of plasma insulin also varied during the female cycle. Insulin was highest in oestrus and lowest in proestrus. Glucagon showed only minor variations. Oestrogen concentrations increased continuously from low values in oestrus to high values in proestrus. These changes were directly related to the changes in the slope of the activity gradient.

Metabolic changes during early starvation in rats fed a low-protein diet in the postweaning growth period

Metabolic changes during the first 24 hours of starvation were studied in rats previously adapted for 3 weeks during the postweaning growth period to a low-protein diet using lactalbumin as a dietary protein source. Previous adaptation to a high-quality, low-protein diet reduced the effects of early starvation on the loss of body and liver weight. In rats fed a low-protein diet (6% lactalbumin, LP rats), free triiodothyronine (T 3) concentration remained higher than in control rats (13% lactalbumin, C rats) throughout the experiment (+38%, 24 hours), and the plasma insulin concentration, which was lower than in C rats during the first 6 hours (−56%), was not different thereafter. Plasma insulin to glucagon molar ratio was lower (−54%) and liver cyclic adenosine monophosphate (cAMP) concentration was higher (+28%) in LP than in C rats in the fed state, but these were not different at 24 hours of starvation. Plasma glucose concentration was slightly lower in LP than in C rats (−15%) in the fed state, but it was not different in both groups during starvation. Whereas they were unchanged in the fed state, plasma lactate concentration was lower (−57%) and free fatty acid and total ketone body concentrations were higher (+38% and + 183%, respectively) in LP than in C rats at 24 hours of starvation. Liver glycogen, fructose-2,6-bisphosphate (F-2,6-P 2), and fructose-1,6-bisphosphate (F-1,6-P 2) concentrations were higher in LP than in C rats in the fed state (+63%, +105%, and +74%, respectively); liver glycogen, F-2,6-P 2, and F-1,6-P 2 concentrations decreased during starvation in both groups and were not different at 24 hours, except for F-2,6-P 2 concentration, which was lower in LP than in C rats (−50%). Liver pyruvate kinase activity measured at 0.4 mmol/L phosphoenolpyruvate (PK v) and pyruvate kinase activity measured at 4 mmol/L phosphoenolpyruvate (PK V) were higher in LP than in C rats over the first 6 hours, and PK v and the PK v PK V ratio were lower at 24 hours of starvation. Liver phosphoenolpyruvate carboxykinase (PEPCK) activity was higher in LP than in C rats in the fed state; during starvation, enzyme activities increased but were not different in both groups. Thus, previous adaptation to a low-protein diet delayed the down-regulation of the glycolytic pathway during the first period of starvation; then, the observed increase in plasma lipids might be consistent with their use as metabolic fuel.

Modulation by oxygen of the glucagon‐dependent activation of the phosphoenolpyruvate carboxykinase gene in rat hepatocyte cultures

In liver phosphoenolpyruvate carboxykinase (PCK) activity, protein and mRNA are localized predominantly in the periportal zone. The activation of the PCK gene by glucagon was studied in primary rat hepatocyte cultures under physiological arterial and venous oxygen tensions [16% and 8% (by vol.)]. PCK gene expression was monitored on the level of transcription, mRNA abundance and enzyme activity as well as enzyme synthesis and degradation. 1. Transcription of the PCK gene was increased by 10 nM glucagon maximally after 0.5 h; it reached nearly basal levels again after 2 h. The increase in transcription was 45% lower under 8% oxygen than under 16% oxygen. 2. PCK mRNA was maximally increased after 2 h under 16% oxygen and after 4 h under 8% oxygen; it subsequently declined to twice the basal values after 8 h. The maximal increase after 2 h was 50% lower under 8% oxygen than under 16% oxygen. 3. PCK enzyme activity was maximally increased after 4-6 h. The maximal enhancement after 4 h was 50% lower under 8% oxygen than under 16% oxygen. 4. The increase in PCK enzyme activity was due to an enhanced synthesis rate of PCK protein. The rate increased after 3 h was 35% lower under 8% oxygen than under 16% oxygen. 5. The degradation of PCK protein was equal under both oxygen tensions. The results show that in cultured rat hepatocytes the induction of PCK gene expression is modulated by physiological concentrations of oxygen. The modulation occurred at the level of gene transcription, mRNA abundance, enzyme protein synthesis and enzyme activity. The periportal to perivenous oxygen gradient could be the major factor responsible for the predominant expression of the PCK gene in the periportal zone.

Subcellular localization of two glutamine‐dependent carbamoyl‐phosphate synthetases and related enzymes in liver of Micropterus salmoides (largemouth bass) and properties of isolated liver mitochondria: Comparative relationship with elasmobranchs

AbstractTwo different glutamine‐dependent carbamoyl‐phosphate synthetase (CPSase) activities are preset in tissues of Squalus acanthias (spiny dogfish shark, a representative elasmobranch) (Anderson, Biochem. J. 261:523–529, 1989). CPSase III (acetylglutamate‐dependent) activity is present in liver mitochondria; the function of this enzyme is related to urea synthesis for the purpose of osmoregulation, and the properties are analogous to the classical ammonia and acetylglutamate‐dependent CPSase I in liver mitochondria of ureotelic species (except that the nitrogen‐donating substrate is glutamine). CPSase II activity is present in spleen and other extrahepatic tissues, but is apparently absent from liver; the function of this enzyme is related to pyrimidine nucleotide biosynthesis, and the properties are analogous to mammalian CPSase II activities (independent of acetylglutamate, inhibited by UTP, and activated by 5‐phosphoribosyl 1‐pyrophosphate). Glutamine synthetase in shark liver is localized in the mitochondria, but the spleen glutamine synthetase is localized in the cytosol. Liver of largemouth bass (Micropterus salmoides, a freshwater teleost) also has CPSase III activity; however, unlike shark, aspartate carbamoyltransferase activity is also present in bass liver. Consequently, a major objective of this study was to establish if two different glutamine‐dependent CPSase activities are present in a single tissue (liver). Two different glutamine‐dependent CPSase activites were found to be present in bass liver, a mitochondrial CPSase III and a cytosolic CPSase II. The CPSase II activity, in contrast to the shark spleen CPSase II, appears to be associated with aspartate carbamoyltransferase and dihydro‐orotase activities, as found in mammalian species. As in shark, ornithine carbamoyltransferase, arginase, and phosphoenolpyruvate carboxykinase activities in bass liver are localized in the mitochondria, but, in contrast to shark, glutamine synthetase activity is localized in the cytosol. The properties of isolated, actively respiring bass liver mitochondria were investigated for comparison with previously reported properties of shark liver mitochondria. Respiration of bass mitochondria is supported by succinate and glutamate plus malate, but not by β‐hydroxybutyrate, palmitoyl‐CoA, citrate, or glutamine, all of which serve as excellent substrates for dogfish shark liver mitochondria. In contrast to shark mitochondria, bass mitochondria are not capable of ketone body formation and, of particular interest, do not catalyze citrulline formation from glutamine. CPSase III activity was not present in two other species of teleost fishes closely related to largemouth bass. The occurrence and function of CPSase III in teleost fishes are discussed.

Inhibition of phosphoenolpyruvate carboxykinase by 6-phosphogluconate in rat liver

Various concentrations of 6-phosphogluconate inhibit rat liver phosphoenolpyruvate carboxykinase activity. 0.04 mM 6-phosphogluconate, which is the concentration found in vivo, caused a 50% inhibition of 6-phosphoenolpyruvate carboxykinase activity. 6-Phosphogluconate lowered the Vmax of the enzyme and increased the concentration of phosphoenolpyruvate required to achieve one-half of the maximum velocity. The role of 6-phosphogluconate as a regulator of the coordination of fluxes through three metabolic pathways is discussed.

Impaired insulin action but normal insulin receptor activity in diabetic rat liver: effect of vanadate

In vivo insulin resistance is a characteristic of the liver and peripheral tissues in 10-wk-old female rats with non-insulin-dependent diabetes induced by streptozotocin given on day 5 after birth. Oral administration of vanadate (0.2 mg/ml) for 20 days in the diabetic rats lowered their plasma glucose levels to normal values without affecting their basal plasma insulin levels. In the basal state as well as after submaximal or maximal hyperinsulinemia (euglycemic clamp studies), peripheral glucose utilization and hepatic glucose production in vivo were normalized in the diabetic rats after the vanadate treatment. In wheat germ agglutinin purified receptors, 125I-labeled porcine insulin binding, basal and insulin-stimulated insulin receptor kinase activities for both the autophosphorylation of the beta-subunit and the phosphorylation of the artificial substrate poly (Glu-Tyr) 4:1, were found identical in diabetic and control rats, treated or not with vanadate. Liver phosphoenolpyruvate carboxykinase activity was significantly enhanced in untreated diabetic rats (P less than 0.01) as compared with control rats and returned to normal values after the 20-day vanadate treatment. Thus, in that model of non-insulin-dependent diabetes, 1) oral vanadate exerts a corrective insulin-like effect on impaired insulin action both at the level of liver and peripheral tissues, 2) impaired insulin action with no alteration of the insulin receptor tyrosine kinase is observed in the liver of untreated rats, and 3) corrective effect of vanadate on liver glucose metabolism is probably distal to the insulin receptor kinase activity.

Effects of starvation and refeeding a high carbohydrate diet on the intra-acinar distribution pattern of phosphoenolpyruvate carboxykinase activity in the liver of male and female rats.

Phosphoenolpyruvate carboxykinase activity in rat liver was shown to be heterotopically distributed within the acinus under varying feeding conditions. Highest values of PEPCK activity were found in the periportal zone of the acinus from where it decreased continuously towards the perivenous zone. 84 h of starvation resulted in an increase of activity, which was most prominent in the perivenous zone, but nevertheless resulted in a steeper gradient. Refeeding of starved rats with a high carbohydrate diet for 6 nights led to a decrease in PEPCK activity which was most prominent in the periportal zone, but almost negligible in the perivenous zone, resulting in a further change in the activity gradient. Sex-dependent differences for total PEPCK activity were found i) in controls, where the activity was lower in females, ii) after starvation, where the induction was much higher in females, and iii) after refeeding of starved rats, where the activity in females remained higher compared to that of the controls. Differences in the intra-acinar localization of the activity in dependence of the sex were registrated in the control group and in starved rats. Livers from female rats contained a higher periportal/perivenous ratio compared to males. In starved and starved and refed animals the periportal/perivenous ratios were almost the same in both sexes.

Effects of metal ions on cattle liver phosphoenolpyruvate carboxykinase activity in vitro.

Effects of metal ions on cattle liver phosphoenolpyruvate carboxykinase activity in vitro.

Metabolic effects induced by long-term feeding of medium-chain triglycerides in the rat

Energy intake, weight gain, carcass composition, plasma hormones and fuels, hepatic metabolites and the activities of phosphoenolpyruvate carboxykinase (PEPCK), malic enzyme, and glucose 6-phosphate dehydrogenase (G6P-DH) were examined in adult rats during a 44-day period of low fat, high carbohydrate (LF) feeding or of consumption of one or two high (70% metabolizable energy) fat diets composed of 63% (metabolizable energy) long-chain (LCT) or medium-chain (MCT) triglycerides. Energy intake was similar in the LCT and MCT groups but was less than that of LF group. The weight gain of rats fed MCT diet was 30% less than that of rats fed LF or LCT diets. Energy retention was less when the diet provided MCT than LCT or LF, and that resulted in a 60% decrease in the daily lipids deposition. Plasma glucose, free fatty acids, glycerol, and insulin/glucagon ratio were similar in the three groups. Blood ketone body (KB) concentrations in rats fed the high fat diets were extremely elevate, particularly in the MCT group, but declined throughout the experiment and by the 44 th day hyperketonemia decreased by 50% but remained higher than in the LF diet. The blood β-hydroxybutyrate/acetoacetate ( B A ) ratio remained slightly elevated in rats fed the high fat diets. Similar changes were observed in liver KB concentration and in the B A ratio. Liver lactate/pyruvate ratio elevated in the LCT and MCT groups at the initiation of the diets decreased by 50% at the end of the experiment. The consumption of high fat diets led to a 1.5-fold increase in liver PEPCK activity. Malic enzyme activity was not altered by the MCT diet, while feeding the LCT diet decreased by 40% malic enzyme activity. By the end of experiment, G6P-DH activity was 25% and 85% lower in MCT and LCT rats than in LF rats. The decrease of ketonemia throughout the experiment in the MCT rats which is associated with a decrease in B A ratio might be due to an adaptation of the rats to the MCT diet (ie, decrease hepatic ketone body production and/or peripheral ketone body utilization).

Lesions in the Lateral Part of the Dorsal Parabrachial Nucleus Caused Hyperphagia and Obesity

For clarification of the role of CCK-8-like immunoreactive neurons in the lateral part of the nucleus parabrachialis dorsalis (PBD), which have fibers projecting to the ventromedial hypothalamus (VMH), the effects of unilateral and bilateral lesions in the lateral part of the PBD on increase in body weight, food and water intake, and metabolism were examined in female Sprague-Dawley rats. Unilateral and bilateral lesions caused significant increases in food and water intake, body weight gain, Lee's index, and the weights of parametrial adipose tissue, liver, and kidney. These lesions resulted in increased serum concentrations of insulin and urea, while the liver phosphoenolpyruvate carboxykinase activity tended to be decreased. These effects were quite similar to, but slightly less than, the effects of bilateral lesions of the VMH. On the side of either unilateral or bilateral lesions, the VMH did not contain CCK-8-like immunoreactive fibers. These findings support the hypothesis that the CCK-8-like immunoreactive neurons in the lateral part of the PBD send signals to the VMH and by relaying signals there they participate in the regulation of food intake and metabolism, their firing suppressing food intake and insulin secretion. However, it is also possible that the lesions induced the above changes by destroying neurons descending and ascending to other brain sites or neural fibers passing through the lesion area.

Phosphoenolpyruvate carboxykinase activity in human liver

The activity of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) (PEPCK), a rate-limiting gluconeogenic enzyme, was found decreased by others in genetically determined disorders and in Sudden Infant Death Syndrome (SIDS). To understand these findings, we made a systematic study of normal human hepatic PEPCK activities in specimens obtained under various conditions from patients not suspected of having SIDS. PEPCK was assayed by the method of Ballard and Hanson [ J. Biol. Chem., 244 (1969) 5625] and activity reported as units (1 μmol/min) per gram protein. Intra-assay precision was 4.1% ( n = 1094); inter-assay precision using the same homogenate was 10.4% ( n = 51); and inter-assay precision using different homogenates of the same tissue specimen was 16.3% ( n = 17). The assay was linear with time and enzyme concentration for at least 60 min up to 1.3 mU/assay and for at least 5 min up to 20 mU/assay. Biopsy specimens had significantly ( P = 0.015) higher PEPCK activity, 12.60 ± 3.01 U/g (range 3.5–10.4, n = 9) compared to specimens obtained at autopsy, 3.20 ± 0.45 U/g (range 0–8.6, n = 33). Specific activity was not significantly correlated with the patient's age, fresh vs. frozen tissue, postmortem intervals up to 68 h, or length of storage at −70°C up to 21 years. One patient had activity at autopsy (tissue obtained < 2 h postmortem) 26% less than was observed in his biopsy specimen. Autopsy samples separated by differential centrifugation into mitochondrial and cytosolic fractions and checked with marker enzymes ornithine transcarbamylase (mitochondrial) and arginase (cytosolic) had considerable cross-contamination between the two fractions in fresh and frozen specimens.

Postnatal hypoglycaemia and gluconeogenesis in the newborn rat. Delayed onset of gluconeogenesis in prematurely delivered newborns.

The concentrations of glucose and lactate in the blood and of liver glycogen, and the phosphoenolpyruvate carboxykinase activity in liver and kidney of term and preterm newborn rats, were studied during the first 6 h post partum. Rates of lactate turnover and gluconeogenesis in vivo from [U-14C]lactate at 3 h and 6 h post partum were also quantified. The development of the prolonged postnatal hypoglycaemia observed after birth in the premature newborn rat is associated with lower rates of glucose production through glycogenolysis and gluconeogenesis; liver glycogenolysis was the main contributing factor to the glucose available during the neonatal period studied in both groups. Delayed induction of liver phosphoenolpyruvate carboxykinase activity was observed in premature newborn rats. Renal phosphoenolpyruvate carboxykinase activity increased 72% from birth in preterm newborns, but only a 25% increase was found in term newborns during the same experimental period. The gluconeogenesis in vivo from [U-14C]lactate paralleled the appearance of cytosolic phosphoenolpyruvate carboxykinase activity in the liver of both groups of newborns. Blood lactate concentrations remained higher in preterm than in term newborns. The postnatal utilization of lactate via the gluconeogenic pathway in either group of newborns was always less than 20% of the total lactate used. The results presented are discussed in relation to the development of postnatal hypoglycaemia and gluconeogenesis in the premature newborn rat.

A Metabolic Comparison of Cysteine and Methionine Supplements in the Diet of a Rat

Adult male Long-Evans rats (250–300 g) were fed diets containing 15% of casein not supplemented with amino acids, supplemented with 0.505% cysteine or supplemented with 0.620% methionine for a period of 17 days. Rats fed the diets supplemented with cysteine had an increased incorporation of the 14C-radioactivity from [U-14C]alanine into liver glycogen and a decreased incorporation from [U-14C]acetate into fatty acids. Pyruvate carboxylase activity was slightly increased and citrate cleavage enzyme activity decreased in the livers of those rats fed the diets supplemented with cysteine. Rats fed diets supplemented with methionine had a decreased liver phosphoenolpyruvate carboxykinase activity. Based on these data it appears that rats fed diets supplemented with cysteine adapt metabolically to store energy as glycogen, while those fed diets supplemented with methionine tend to store energy as lipid.

Influence of endotoxin treatment on dexamethasone induction of hepatic phosphoenolpyruvate carboxykinase.

Decreased glucocorticoid binding has been observed at a time after endotoxin (3 to 6 h) when imparied liver enzyme induction is known to occur. This study was undertaken to characterize the early time course of hypoglycemia and decreased liver phosphoenolpyruvate carboxykinase (PEPCK) activity in intact and adrenalectomized mice given endotoxin. In addition, altered steroid induction of hepatic PEPCK was examined in adrenalectomized mice given dexamethasone at intervals before and after a median lethal dose of endotoxin. Intact mice demonstrated a dramatic hyperglycemia at 1 h after endotoxin treatment, a response absent in adrenalectomized mice. Plasma glucose levels were significantly reduced from control values at 3 and 6 h posttreatment, with the most pronounced endotoxin-induced hypoglycemia seen in adrenalectomized mice. Hepatic PEPCK activity in intact mice given endotoxin was decreased at 3 and 6 h after treatment, although no change from basal, noninduced levels was seen in poisoned adrenalectomized mice. The increased increment in hepatic PEPCK activity due to fasting of intact control mice was reproduced in adrenalectomized control mice by the administration of dexamethasone. Furthermore, the induction of hepatic PEPCK by dexamethasone was inhibited by 1 h after endotoxin treatment, with enzyme activity falling to basal, noninduced levels by 6 h posttreatment. At these same time intervals after endotoxin treatment, no evidence of histopathology in the liver or adrenal glands was seen. These results coincide with changes in steroid binding seen previously and indicate that endotoxin treatment produces significant alterations in glucocorticoid action at the subcellular or molecular level.

Hyperglycémie maternelle et développement foetal chez le rat : conséquences d'une perfusion continue de glucose à la rate en fin de gestation

Continuous glucose infusion was used to induce mild hyperglycemia in unrestrained pregnant rats during the last three days of pregnancy. Control rats were infused with distilled water. Compared with the controls, fetuses from glucose-infused rats showed higher plasma glucose levels, increased plasma insulin and lower plasma glucagon concentrations. Pregnancy prolonged until day 23.5 resulted in a sharp decrease in plasma insulin concentrations and a dramatic increase in plasma glucagon concentrations. In 23.5-day old fetuses from both groups, plasma insulin concentration rose when phentolamine was injected but not when propanolol was injected. Plasma glucagon concentration in 23.5-day old fetuses from glucose-infused rats dropped with propanolol injection. In fetuses from control rats, liver phosphoenolpyruvate activity increased markedly and liver glycogen stores decreased sharply. In fetuses from glucose-infused rats, liver phosphoenolpyruvate carboxykinase activity rose and glycogen content decreased, but to a lesser degree. Moreover, in postmature fetuses from glucose-infused rats, elevated plasma glucose and insulin concentrations were related to increased body weight and total carcass fat. Concurrently, the rate of lipogenesis in the carcass of these fetuses (estimated from the incorporation of 3H from 3H2O into fatty acids) was significantly increased.

Response of rainbow trout (Salmo gairdneri) to increased levels of available carbohydrate in practical trout diets.

1. The physiological response of rainbow trout (Salmo gairdneri) reared on different levels of available carbohydrate in practical trout diets having the same levels of energy and nitrogen for 16-24 weeks was determined. 2. Weight gain was significantly reduced in trout reared on the highest level of available carbohydrate, 210 g cerelose (alpha-glucose) kg, and there was a significant linear regression (R2 0.88 of dietary carbohydrate on weight gain. 3. Liver: body-weight values and liver glycogen levels increased in relation to increased dietary carbohydrate. 4. Liver glucose-6-phosphate dehydrogenase (EC 1.1.1.49) activity increased and liver phosphoenolpyruvate carboxykinase (EC 4.1.1.32) activity decreased per kg body-weight of fish with increasing dietary carbohydrate. However, no significant effect was noted on the activity of these liver enzymes above a dietary cerelose level of 140 g/kg. 5. Liver fructose diphosphatase (EC 3.1.3.11) activity increased with increasing dietary carbohydrate has been interpreted as meaning a recycling of triosephosphate to glucose-6-phosphate. 6. Dietary carbohydrate level had no significant effect on the liver pyruvate kinase (EC 2.7.1.40) activity, the rate of glucose utilization or the percentage conversion of [14C]alanine to glucose in the plasma of trout. 7. The results indicate that rainbow trout have a limited ability to adapt to increased dietary carbohydrate and a level in excess of 140 g/kg of the diet is not efficiently utilized.