Postmaturity in the rat: glucose metabolism in the fetus and the neonate

The present study was designed to investigate glucose metabolism in the postmature fetus and newborn. In the fetus, the decreased hepatic glycogen content together with the decrease by the same percentage of total hepatic glycogen radioactivity from directly injected [6-3H]glucose demonstrate that fetal glycogenolysis occurs during prolonged gestation. Moreover, fetal glycogen synthesis as tested by in vivo [6-3H]glucose incorporation experiments is inhibited. In vivo experiments with [14C]lactate are consistent with gluconeogenesis, being inactive in the postmature fetus as well as in the normal-term fetus. During the first hr after delivery, our in vivo data about conversion of [14C]lactate to glucose show that the gluconeogenic pathway is not functioning in spite of very high phosphoenolpyruvate carboxykinase activity in the postmature. By 3 hr postpartum, the phosphoenolpyruvate carboxykinase activity, the blood lactate level, the percentage of conversion, and the rate of gluconeogenesis are very elevated in the postmatures as compared to the term neonates. By 6 hr postpartum, despite maintained phosphoenolpyruvate carboxykinase activity, gluconeogenic rate becomes very weak in postmatures kept fasting. This is the time characterized by a profound hypoglycemia. In contrast, fed postmature neonates exhibit normal blood glucose levels by 6 and 12 hr postpartum as a result of sustained rate of gluconeogenesis.     

Effects of metformin on glucose and glucagon regulated gluconeogenesis in cultured normal and diabetic hepatocytes

The effects of glucose and glucagon on the anti-gluconeogenic action of metformin were investigated in normal and diabetic hepatocytes. Glucose production from lactate was elevated by 88% in hepatocytes from fasted normal rats compared with hepatocytes from fed animals. Diabetes caused 3.5- and 2.1-fold increases in hepatic gluconeogenesis under fasting and fed conditions, respectively. Metformin (250 microM) suppressed glucose production by 37% in normal and by 30% in diabetic hepatocytes from fed rats. This drug was more effective (up to 67%) with increasing concentrations of glucose in the medium. Potentiation by metformin of insulin action on gluconeogenesis was elevated significantly (P < 0.01 to 0.001) by glucose in vitro. Metformin (75-250 microM) also counteracted the effects of glucagon at optimal concentrations in normal (32-68%) as well as diabetic (8-46%) hepatocytes. The findings of this study indicate that (i) the anti-gluconeogenic effect of metformin is enhanced by glucose in vivo and in vitro; and (ii) the suppression of glucagon-induced gluconeogenesis by metformin could play a role in its glucose-lowering effects in diabetic conditions.     

The role of the locus coeruleus and N-methyl-D-aspartic acid (NMDA) and AMPA receptors in opiate withdrawal

The turnover rates of plasma lactate, normalized for O2 consumption rate, are higher in the fetus than in the adult. This occurs despite very low rates of fetal gluconeogenesis which preclude the recycling of lactate carbon into glucose. In an effort to establish the main routes of disposal of fetal plasma lactate, 12 midgestation ovine fetuses (age 74 +/- 1 days) were infused intravenously at constant rate with L-[U-14C]lactate for a 4-hour period. At the end of the infusion, the amounts of 14C retained by the fetus and by the placenta, and the distribution of the retained 14C in free and protein-bound amino acids and in lipids were measured. Of the total 14C infused, 17.0 +/- 1.4% was recovered in the placenta, 4.0 +/- 0.3% in the fetal liver, and 15.0 +/- 0.8% in the extrahepatic fetal tissues. Of the retained radioactive carbon, 45-57% was recovered in the free and protein-bound amino acid fractions and 11-17% in the lipid fractions. Approximately 90% of the 14C in the free amino acid fractions was present as glutamate/glutamine, serine, glycine, and alanine carbon. In conjunction with data on fetal CO2 production from lactate carbon, these results demonstrate that the main routes of fetal lactate disposal are oxidation and synthesis of nonessential amino acids and lipids.     

Modulation of epinephrine-stimulated gluconeogenesis by insulin in hepatocytes isolated from genetically obese (fa/fa) Zucker rats

Genetically obese (fa/fa) Zucker rats present an impaired response of hepatic glucose production to the inhibition by insulin. In this work, we have investigated the modulation by this hormone of epinephrine-stimulated gluconeogenesis, in hepatocytes isolated from obese (fa/fa) rats and their lean (Fa/-) littermates. Epinephrine (1 microM) caused a maximal stimulation of [14C]lactate conversion to [14C]glucose in hepatocytes isolated from either obese or lean animals. The stimulation of gluconeogenesis by epinephrine was accompanied by a significant reduction of fructose 2,6-bisphosphate levels, an inactivation of both pyruvate kinase and 6-phosphofructo 2-kinase, and by a 2-fold increase in the cellular concentrations of cAMP. The presence of insulin in the incubation medium antagonized, in a concentration-dependent manner, the effects of epinephrine. In hepatocytes isolated from lean rats, the reversion caused by insulin was complete, the concentration required for half-maximal insulin action ranging from 0.22 to 0.56 nM. In contrast, in obese rat hepatocytes, insulin only partially blocked epinephrine-mediated effects, and the sensitivity to insulin was 2- to 4-fold lower, as indicated by the corresponding half-maximal insulin action values. Furthermore, insulin (10 nM) almost completely blocked the increase in cAMP levels induced by epinephrine in lean rat hepatocytes, whereas it only provoked a small and nonsignificant reduction of epinephrine-stimulated levels of the cyclic nucleotide in hepatocytes obtained from obese rats.     

Effect of troglitazone (Rezulin) on fructose 2,6-bisphosphate concentration and glucose metabolism in isolated rat hepatocytes

The effect of troglitazone, an orally effective thiazolidinedione, on lactate- and glucagon-stimulated gluconeogenesis (in the absence of insulin) was examined in hepatocytes isolated from rats under different nutritional states. Hepatocytes obtained from fed or 20-24 hr fasted male Sprague-Dawley rats were incubated in Krebs-Henseleit Bicarbonate buffer (KHBC) (in presence or absence of 10.0 mM glucose) containing 2.0 mM [U-14C]lactate (0.1-0.25 microCi) with or without 10.0 nM glucagon and troglitazone (30.0 microM) or the appropriate vehicle. Aliquots were removed at specified endpoints and assayed for glucose and fructose 2,6-bisphosphate (F-2,6-P2) concentrations. In 20-24 hour starved hepatocytes, troglitazone produced a 26.1% inhibition of lactate-stimulated gluconeogenesis. This inhibitory effect of troglitazone on hepatic gluconeogenesis was further potentiated by incubation of the cells with glucose in vitro. In hepatocytes obtained from fasted rats (and incubated with 10 mM glucose in vitro) troglitazone reduced lactate-and glucagon-stimulated gluconeogenesis by 53% and 56%, respectively. This reduction in hepatic glucose production was associated with 1.06 and 1.04 fold increase in the hepatocyte F-2,6-P2 content. In isolated hepatocytes from fed animals and incubated with 10 mM glucose in vitro, troglitazone (15 and 30 microM) did not have any effect on either lactate- or glucagon-stimulated gluconeogenesis. However, 30 microM troglitazone significantly enhanced (36%) F-2,6-P2 concentrations during lactate-stimulated gluconeogenesis. These findings demonstrate that troglitazone decreases hepatic glucose production through alterations in the activity of one or more gluconeogenic/glycolytic enzymes, depending upon the nutritional state of the animal and the presence or absence of hormonal modulation. All of the effects of troglitazone in the present study were observed in the absence of insulin, suggesting an "insulinomimetic" effect. However, this does not exclude the possibility that troglitazone may also function as an "insulin sensitizer" in hepatic and certain other tissues.     

A decreased metabolic clearance of glucose is involved in the hyperglycemic effect of a serum temperature induced factor (TIF)

We have studied the effects of a hyperglycemic temperature induced factor (TIF) on glucose metabolism, in 3 groups of Wistar rats: 10 rats injected with non-heated serum, 10 rats injected with heated serum and 10 rats injected with semi-purified TIF. Seric levels of insulin and glucagon were not modified in rats injected with heated serum. The injection of heated serum induced hyperglycemia (p < 0.0001), a decrease of lactate (p < 0.001) and pyruvate (p < 0.05) levels, and an increase of acetoacetate level (p < 0.001). The levels of beta hydroxybutyrate and amino acids (alanine and glutamine) were not changed. Glucose turn over rate (12.3 +/- 1.3 g/min/kg) and metabolic clearance of glucose (10.0 +/- 0.8 ml/min/kg) were significantly lower in rats treated with heated serum and purified TIF than in controls (respectively, p < 0.05 and p < 0.001). These data suggested that the hyperglycemic effect of heated serum and isolated TIF could correspond to an impaired metabolic clearance of glucose and to an increased gluconeogenesis.     

Effects of branched-chain-enriched amino acid solution on insulin and glucagon secretion and blood glucose level in liver cirrhosis

BACKGROUND: The aim of this study was to determine whether therapeutically used branched-chain amino acids (BCAAs) solution influences glucose metabolism in liver cirrhosis (LC). METHODS: BCAAs solution (200 ml) was infused in LC patients at different stages, and plasma concentrations of glucose and pancreatic hormones were determined. RESULTS: In patients with mild LC, BCAAs caused a significant increase in glucose level (maximal increment, 12.5+/-2.5 mg/dl) with a great increase in insulin (maximal increment, 39.5+/-8.3 microU/ml) and a small increase in glucagon secretion (maximal increment, 101.0+/-16.0 pg/ml). In patients with advanced LC, BCAAs caused a great increase in glucagon secretion (220.5+/-19.4 pg/ml) with only a slight increase in glucose levels (5.8+/-2.2 mg/dl). CONCLUSION: BCAAs solution causes hyperglycemia in mild LC due to insulin resistance, whereas it causes only a slight increase in severe LC due to hepatic glucagon resistance. Thus, there is a possibility that BCAAs solution may lead to hypoglycemia in advanced LC with hepatic glycogen depletion.     

Ingested interferon alpha suppresses type I diabetes in non-obese diabetic mice

Glutamine is an important gluconeogenic amino acid in postabsorptive humans. To assess the effect of glucagon on renal and hepatic glutamine gluconeogenesis, we infused six normal healthy postabsorptive subjects with glucagon at a rate chosen to produce circulating glucagon concentrations found during hypoglycemia and, using a combination of isotopic and net balance techniques, determined the systemic, renal, and hepatic glucose release and renal and hepatic production of glucose from glutamine. Infusion of glucagon increased systemic and hepatic glucose release (both P < .02), but had no effect on renal glucose release (P = .26). Systemic and hepatic glutamine gluconeogenesis increased from 0.45 +/- 0.3 and 0.11 +/- 0.02 micromol x kg(-1) x min(-1), respectively, to 0.61 +/- 0.04 (P = .002) and 0.31 +/- 0.03 micromol x kg(-1) x min(-1) (P = .001), respectively, whereas renal glutamine gluconeogenesis was unchanged (from 0.33 +/- 0.03 to 0.30 +/- 0.04 micromol x kg(-1) x min(-1), P = .20). The hepatic contribution to systemic glutamine gluconeogenesis increased from 25.2% +/- 6.2% to 51.6% +/- 5.5% (P = .002), while that of the kidney decreased from 74.8% +/- 6.2% to 48.4% +/- 5.5% (P = .003). Glucagon had no effect on the renal net balance, fractional extraction, or uptake and release of either glucose or glutamine. We thus conclude that glucagon stimulates glutamine gluconeogenesis in normal postabsorptive humans, predominantly due to an increase in hepatic glutamine conversion to glucose. Thus, under certain conditions such as counterregulation of hypoglycemia, the liver may be an important site of glutamine gluconeogenesis.     

Effect of environmental temperature on glucose-induced insulin response in the newborn rat

Blood glucose and plasma insulin and glucagon concentrations were determined in full-term rats delivered by cesarean section and exposed to 37 degrees C. or 24 degrees C. environmental temperature during the first hours of extrauterine life. When newborn rats were maintained at thermal neutrality (37 degrees C.), a transient period of hypoglycemia of two hours occurred, associated with a rapid fall in plasma insulin and a rise in plasma glucagon concentrations. During cold exposure (24 degrees C.), the blood glucose level remained stable over the four hours studied; the decrease of plasma insulin was sluggish while the rise of plasma glucagon was unchanged. In newborn rats maintained at 37 degrees C., an intraperitoneal glucose load one hour after delivery produced a marked rise in blood glucose and plasma insulin concentrations one hour later. The distribution of experimental points suggested a sigmoidal dose-response curve. By contrast in newborn rats kept at room temperature (24 degrees C.) the same glucose load did not induce any increase in plasma insulin in spite of hyperglycemia. However, phentolamine resulted in pronounced plasma insulin rise in hypothermic newborns in response to glucose administration. From these observations it is concluded that the in-vivo unresponsiveness of the beta cells to glucose at birth, reported by others, is mainly due to the experimental conditions.     

The effects of non-insulin-dependent diabetes mellitus on the kinetics of onset of insulin action in hepatic and extrahepatic tissues

The mechanism(s) of insulin resistance in non-insulin-dependent diabetes mellitus remains ill defined. The current studies sought to determine whether non-insulin-dependent diabetes mellitus is associated with (a) a delay in the rate of onset of insulin action, (b) impaired hepatic and extrahepatic kinetic responses to insulin, and (c) an alteration in the contribution of gluconeogenesis to hepatic glucose release. To answer these questions, glucose disappearance, glucose release, and the rate of incorporation of 14CO2 into glucose were measured during 0.5 and 1.0 mU/kg-1 per min-1 insulin infusions while glucose was clamped at approximately 95 mg/dl in diabetic and nondiabetic subjects. The absolute rate of disappearance was lower (P < 0.05) and the rate of increase slower (P < 0.05) in diabetic than nondiabetic subjects during both insulin infusions. In contrast, the rate of suppression of glucose release in response to a change in insulin did not differ in the diabetic and nondiabetic subjects during either the low (slope 30-240 min:0.02 +/- 0.01 vs 0.02 +/- 0.01) or high (0.02 +/- 0.00 vs 0.02 +/- 0.00) insulin infusions. However, the hepatic response to insulin was not entirely normal in the diabetic subjects. Both glucose release and the proportion of systemic glucose being derived from 14CO2 (an index of gluconeogenesis) was inappropriately high for the prevailing insulin concentration in the diabetic subjects. Thus non-insulin-dependent diabetes mellitus slows the rate-limiting step in insulin action in muscle but not liver and alters the relative contribution of gluconeogenesis and glycogenolysis to hepatic glucose release.     

Changes in hepatic nitrogen balance in plasma concentrations of amino acids and hormones and in cell volume after overnight fasting in perinatal and adult rat

Important regulatory factors of intrahepatic protein synthesis and proteolysis are amino acids, glucagon, insulin, and cell volume. We have investigated the changes in these factors with development and after an overnight fast and evaluated their contribution to changes in the hepatic nitrogen balance in vivo. In the fed state, glucagon levels were highest in suckling animals and gradually declined in older rats, whereas the concentration of insulin increased during development. The amino acid concentrations in liver and plasma declined during the suckling period to levels that in vitro are highly permissive for induction of autophagic proteolysis. In all age groups investigated, fasting was associated with a drop in hepatic protein content, together with a marked decrease in hepatocellular volume and insulin concentrations. On the other hand, glucagon concentrations and the concentration of many amino acids in plasma and liver responded to fasting with a pronounced decrease in perinatal and suckling animals, but this response had become blunted at weaning and had disappeared in adult animals. These findings suggest that insulin and/or hepatocellular volume are more likely candidates as short-term physiologic regulators of the hepatic nitrogen balance than are glucagon or amino acids. In glucose-supplemented fetuses, high levels of insulin could not compensate for a decreased hepatocellular volume in averting a catabolic state, suggesting that cell volume is the more important factor. Although our study cannot discriminate between the effects of fasting on protein synthesis and degradation, our findings show unequivocally that, for a rapid growth of the liver, suckling animals have to be fed around-the-clock.     

Mechanisms of liver and muscle insulin resistance induced by chronic high-fat feeding

To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.     

Counterregulation by epinephrine and glucagon during insulin-induced hypoglycemia in the conscious dog

We assessed the combined role of epinephrine and glucagon in regulating gluconeogenic precursor metabolism during insulin-induced hypoglycemia in the overnight-fasted, adrenalectomized, conscious dog. In paired studies (n = 5), insulin was infused intraportally at 5 mU.kg-1.min-1 for 3 h. Epinephrine was infused at a basal rate (B-EPI) or variable rate to simulate the normal epinephrine response to hypoglycemia (H-EPI), whereas in both groups the hypoglycemia-induced rise in cortisol was simulated by cortisol infusion. Plasma glucose fell to approximately 42 mg/dl in both groups. Glucagon failed to rise in B-EPI, but increased normally in H-EPI. Hepatic glucose release fell in B-EPI but increased in H-EPI. In B-EPI, the normal rise in lactate levels and net hepatic lactate uptake was prevented. Alanine and glycerol metabolism were similar in both groups. Since glucagon plays little role in regulating gluconeogenic precursor metabolism during 3 h of insulin-induced hypoglycemia, epinephrine must be responsible for increasing lactate release from muscle, but is minimally involved in the lipolytic response. In conclusion, a normal rise in epinephrine appears to be required to elicit an increase in glucagon during insulin-induced hypoglycemia in the dog. During insulin-induced hypoglycemia, epinephrine plays a major role in maintaining an elevated rate of glucose production, probably via muscle lactate release and hepatic lactate uptake.     

Peripheral but not hepatic insulin resistance in mice with one disrupted allele of the glucose transporter type 4 (GLUT4) gene

Glucose transporter type 4 (GLUT4) is insulin responsive and is expressed in striated muscle and adipose tissue. To investigate the impact of a partial deficiency in the level of GLUT4 on in vivo insulin action, we examined glucose disposal and hepatic glucose production (HGP) during hyperinsulinemic clamp studies in 4-5-mo-old conscious mice with one disrupted GLUT4 allele [GLUT4 (+/-)], compared with wild-type control mice [WT (+/+)]. GLUT4 (+/-) mice were studied before the onset of hyperglycemia and had normal plasma glucose levels and a 50% increase in the fasting (6 h) plasma insulin concentrations. GLUT4 protein in muscle was approximately 45% less in GLUT4 (+/-) than in WT (+/+). Euglycemic hyperinsulinemic clamp studies were performed in combination with [3-3H]glucose to measure the rate of appearance of glucose and HGP, with [U-14C]-2-deoxyglucose to estimate muscle glucose transport in vivo, and with [U-14C]lactate to assess hepatic glucose fluxes. During the clamp studies, the rates of glucose infusion, glucose disappearance, glycolysis, glycogen synthesis, and muscle glucose uptake were approximately 55% decreased in GLUT4 (+/-), compared with WT (+/+) mice. The decreased rate of in vivo glycogen synthesis was due to decreased stimulation of glucose transport since insulin's activation of muscle glycogen synthase was similar in GLUT4 (+/-) and in WT (+/+) mice. By contrast, the ability of hyperinsulinemia to inhibit HGP was unaffected in GLUT4 (+/-). The normal regulation of hepatic glucose metabolism in GLUT4 (+/-) mice was further supported by the similar intrahepatic distribution of liver glucose fluxes through glucose cycling, gluconeogenesis, and glycogenolysis. We conclude that the disruption of one allele of the GLUT4 gene leads to severe peripheral but not hepatic insulin resistance. Thus, varying levels of GLUT4 protein in striated muscle and adipose tissue can markedly alter whole body glucose disposal. These differences most likely account for the interindividual variations in peripheral insulin action.     

Importance of peripheral insulin levels for insulin-induced suppression of glucose production in depancreatized dogs

It is generally believed that glucose production (GP) cannot be adequately suppressed in insulin-treated diabetes because the portal-peripheral insulin gradient is absent. To determine whether suppression of GP in diabetes depends on portal insulin levels, we performed 3-h glucose and specific activity clamps in moderately hyperglycemic (10 mM) depancreatized dogs, using three protocols: (a) 54 pmol.kg-1 bolus + 5.4 pmol.kg-1.min-1 portal insulin infusion (n = 7; peripheral insulin = 170 +/- 51 pM); (b) an equimolar peripheral infusion (n = 7; peripheral insulin = 294 +/- 28 pM, P < 0.001); and (c) a half-dose peripheral infusion (n = 7), which gave comparable (157 +/- 13 pM) insulinemia to that seen in protocol 1. Glucose production, use (GU) and cycling (GC) were measured using HPLC-purified 6-[3H]- and 2-[3H]glucose. Consistent with the higher peripheral insulinemia, peripheral infusion was more effective than equimolar portal infusion in increasing GU. Unexpectedly, it was also more potent in suppressing GP (73 +/- 7 vs. 55 +/- 7% suppression between 120 and 180 min, P < 0.001). At matched peripheral insulinemia (protocols 2 and 3), not only stimulation of GU, but also suppression of GP was the same (55 +/- 7 vs. 63 +/- 4%). In the diabetic dogs at 10 mM glucose, GC was threefold higher than normal but failed to decrease with insulin infusion by either route. Glycerol, alanine, FFA, and glucagon levels decreased proportionally to peripheral insulinemia. However, the decrease in glucagon was not significantly greater in protocol 2 than in 1 or 3. When we combined all protocols, we found a correlation between the decrements in glycerol and FFAs and the decrease in GP (r = 0.6, P < 0.01). In conclusion, when suprabasal insulin levels in the physiological postprandial range are provided to moderately hyperglycemic depancreatized dogs, suppression of GP appears to be more dependent on peripheral than portal insulin concentrations and may be mainly mediated by limitation of the flow of precursors and energy substrates for gluconeogenesis and by the suppressive effect of insulin on glucagon secretion. These results suggest that a portal-peripheral insulin gradient might not be necessary to effectively suppress postprandial GP in insulin-treated diabetics.     

Gluconeogenesis in infancy and childhood. I. A method for the study of the in vivo gluconeogenesis from alanine and glycerol

The in vivo gluconeogenesis from alanine and glycerol in infants and children was studied by an isotope method, using 14C-labeled substates with subsequent separation of the radioactive compounds by thin-layer chromatography. Seven patients, aged 2 months to 2 years 11 months, with normal carbohydrate metabolism were studied. Trace amounts of [14C]alanine were injected intravenously in four fasting patients. The 14C moved quickly from alanine to lactate, with a peak activity in lactate obtained before 5 min. From 10 min on, the label disappeared rapidly from both. An equilibrium was established between alanine and lactate, displaced towards lactate. The peak activity in glucose was reached in 10-20 min, amounting to 10% of total injected activity. In one patient, who was also studied after a meal, the disappearance rate of alanine was reduced by 50%. Despite this reduction the appearance of label in lactate was increased, whereas the amount of label in glucose was much reduced. [14C]glycerol was injected intravenously in three fasting patients. In one patient, who received only a tracer dose of glycerol, 5 times more 14C appeared in glucose than in the patients studied with [14C]alanine. In two patients receiving a glycerol load together with the [14C]glycerol, the disappearance rate of glycerol was markedly reduced, as was the conversion of carbon to glucose and lactate.     

Protein: metabolism and effect on blood glucose levels

Insulin is required for carbohydrate, fat, and protein to be metabolized. With respect to carbohydrate from a clinical standpoint, the major determinate of the glycemic response is the total amount of carbohydrate ingested rather than the source of the carbohydrate. This fact is the basic principle of carbohydrate counting for meal planning. Fat has little, if any, effect on blood glucose levels, although a high fat intake does appear to contribute to insulin resistance. Protein has a minimal effect on blood glucose levels with adequate insulin. However, with insulin deficiency, gluconeogenesis proceeds rapidly and contributes to an elevated blood glucose level. With adequate insulin, the blood glucose response in persons with diabetes would be expected to be similar to the blood glucose response in persons without diabetes. The reason why protein does not increase blood glucose levels is unclear. Several possibilities might explain the response: a slow conversion of protein to glucose, less protein being converted to glucose and released than previously thought, glucose from protein being incorporated into hepatic glycogen stores but not increasing the rate of hepatic glucose release, or because the process of gluconeogenesis from protein occurs over a period of hours and glucose can be disposed of if presented for utilization slowly and evenly over a long time period.     

Hypothalamic influence on insulin and glucagon release in the rat

Blood glucose, plasma insulin, and glucagon levels were measured in undisturbed and free-moving rats. The insulin and glucagon levels rise in the 1st min after the beginning of food ingestion, whereas the glucose level begins to increase only in the 3rd min if carbohydrate-rich food is eaten. This early rise in insulin and glucagon level is also observed under conditions in which carbohydrate-free food is eaten. A similar release of insulin and glucagon can be obtained by injection of 0.1 microgram of norepinephrine into the ventromedial hypothalamus, but the same injection made into the lateral hypothalamus causes release of insulin only, whereas injections in other hypothalamic areas are nearly without effect. Similar injections of isoproterenol did not cause changes in insulin, glucagon, and glucose levels. It is suggested that the early insulin and glucagon responses are of reflex origin and that the ventromedial and lateral hypothalamic areas are relay stations in the reflex pathways. The lack of effect of atropine to block the insulin and glucagon responses to noradrenergic stimulation of the ventromedial hypothalamus indicates that the efferent pathway is not cholinergic.     

Evaluation of glucose metabolic disorder: insulin resistance and insulin receptors in critically ill children

OBJECTIVE: To explore the pathogenesis of glucose metabolic disorder and insulin resistance in critically ill children under severe stress. METHODS: To test glucose, lactate, glucagon, insulin, c-peptide, cortisol levels in 50 critically ill children. While we measured 125I-insulin binding to erythrocytes of 13 critically ill children who had hyperglycemia and hyperinsulinemia. Glucose and lactate were measured biochemically. Insulin, c-peptide, cortisol and glucagon were determined by RIA. Erythrocytes insulin receptor was detected by insulin radioreceptor assay. RESULTS: Glucose, lactate, insulin, c-peptide, glucagon, cortisol, insulin/glucose, insulin/glucagon ratio in patients were higher than those in normal controls (P < 0.05). As compared with normal controls, the maximum 125I-insulin bound and insulin receptor number per cell were significantly lower (P < 0.01). But there was no difference of mean value in receptor affinity (P > 0.05). CONCLUSIONS: Hyperglycemia is common in critically ill children during stress, which may be attributed to hormones disturbance and tissure insulin resistance. Insulin receptor defect due to comprehensive factors was one of the important causes for insulin resistance. The blood glucose level can be used as an predicting index in ICU.     

Comparative effects of englitazone and glyburide on gluconeogenesis and glycolysis in the isolated perfused rat liver

Englitazone (CP 68,722, Pfizer) is a member of a family of drugs known as thiazolidinediones. One member of this family, troglitazone (Rezulin), is currently utilized in the treatment of Type 2 diabetes. Previous studies have focused on the ability of englitazone to increase insulin sensitivity in various tissues. However, little information is available regarding the direct effect of englitazone on hepatic glucose metabolism in the absence of insulin. Therefore, the following studies were conducted to comparatively evaluate the effect of englitazone and glyburide (a representative sulfonylurea) on gluconeogenesis and glycolysis from various substrates in the isolated perfused rat liver (IPRL). In isolated perfused rat livers of 24-hr fasted rats infused with lactate (2 mM), englitazone (6.25 to 50 microM) produced a concentration-dependent decrease (32-93%) in hepatic gluconeogenesis. When dihydroxyacetone (1 mM) and fructose (1 mM) were used as metabolic substrates, englitazone inhibited gluconeogenesis by 31 and 15%, respectively, while increasing glycolysis by 42 and 50%. Similar effects on gluconeogenesis and glycolysis were observed with glyburide, even though the effects with glyburide were more acutely evident, reversible, and of a greater magnitude. Such data suggest alterations in hepatic glucose production may contribute to the decrease in plasma glucose concentrations observed in individuals treated with englitazone and glyburide. These alterations may include effects on several regulatory enzymes (e.g. fructose-1,6-bisphosphatase, pyruvate kinase, and phosphoenolpyruvate carboxykinase), which warrant further investigation.