Effect of phenylephrine on pyruvate dehydrogenase activity in rat hepatocytes and its interaction with insulin and glucagon

AbstractIn isolated rat hepatocytes phenylephrine promotes a rapid increase in the amount of pyruvate dehydrogenase present in its active form (PDHa). This action is mediated by α1-adrenergic receptors and is not observed in Ca2+-depleted hepatocytes. It is mimicked by the Ca2+ ionophore A23187. No changes in metabolites known to affect PDH activity are measured 3 min after addition of phenylephrine. Glucagon also increases PDHa, its action is additive to that of phenylephrine. The action of phenylephrine on PDHa could be explained by an increase in mitochondrial free Ca2+

Persistent Correlation of Ghrelin Plasma Levels with Body Mass Index Both in Stable Weight Conditions and during Gastric-bypass-induced Weight Loss

Background: Studies done on serial changes in plasma ghrelin levels after gastric bypass (GBP) have yielded contrasting results since decreased, unchanged, or increased levels have been reported in the literature. This study investigates whether or not GBP has an inhibitory effect on fasting ghrelin levels independently of weight loss. Methods: Fasting ghrelin levels were measured in 115 stable body weight females, classified as normal body weight (NW; body mass index (BMI) 50kg/m2). Results: Each obese subgroup showed significantly lower ghrelin levels as compared to both NW (p < 0.0001) and OW subjects (p < 0.05 or 0.005); however, no significant differences were observed within the three obese subgroups. Forty-nine obese patients underwent a GBP. Plasma ghrelin, measured at 3, 6, and 12months after GBP, significantly increased from the sixth month on (p < 0.0001). When patients were classified, at each postoperative time point, according to their actual BMI, ghrelin was significantly (p = 0.0002) related to postoperative BMI and not significantly different from ghrelin measured in stable body weight conditions. Conclusions: Fasting ghrelin displays an inversely significant correlation with BMI in both stable body weight conditions and after GBP. No evidence was found that GBP had an effect on fasting ghrelin levels, independent of weight los

The effect of insulin on cardiac autonomic balance predicts weight reduction after gastric bypass

Aims/hypothesis: The aim of this study was to assess the predictive role of autonomic reactivity in body weight loss induced by gastric bypass. Methods: A group of 22 morbidly obese subjects, who were due to undergo a gastric bypass, were submitted, before surgery, to a euglycaemic-hyperinsulinaemic clamp, during which a continuous recording of the ECG was performed. The effect of insulin on cardiac autonomic balance was evaluated by performing power spectral analysis of heart rate variability. The low-to-high frequency ratio was calculated before and during the clamp and its modifications were expressed as % delta low-to-high frequency ratio (%Δ L: H). Results: Preoperative %Δ L: H showed a significant (p=0.0009, r 2=0.43), positive relationship to the reduction of body weight, measured 1 year after surgery and expressed as % excess weight loss (% EWL). Preoperative BMI was also significantly (p=0.0009, r 2=0.43) negatively related to the 12-month % EWL. In a multiple regression analysis, %Δ L: H remained a significant (p=0.003), independent predictor of body weight loss, even when preoperative BMI or age, % fat mass, insulinaemia and glucose disposal were taken into account. Conclusions/interpretation: The best correction of excess body weight was achieved by those obese subjects who had a preserved capacity to shift their cardiac autonomic balance towards a sympathetic prevalence in response to an euglycaemic-hyperinsulinaemic clamp. Further studies are needed to elucidate the mechanisms through which the autonomic nervous system influences weight reductio

Increasing uncoupling protein-2 in pancreatic beta cells does not alter glucose-induced insulin secretion but decreases production of reactive oxygen species

Aims/hypothesis: Levels of uncoupling protein-2 (UCP2) are regulated in the pancreatic beta cells and an increase in the protein level has been associated with mitochondrial uncoupling and alteration in glucose-stimulated insulin secretion. However, it is not clear whether an increase in uncoupling protein-2 per se induces mitochondrial uncoupling and affects ATP generation and insulin secretion. Materials and methods: Transgenic mice with beta cell-specific overexpression of the human UCP2 gene and INS-1 cells with doxycycline-inducible overproduction of the protein were generated and the consequences of increased levels of UCP2 on glucose-induced insulin secretion and on parameters reflecting mitochondrial uncoupling were determined. Results: In transgenic mice, an increase in beta cell UCP2 protein concentration did not significantly modify plasma glucose and insulin levels. Glucose-induced insulin secretion and elevation in the ATP/ADP ratio were unaltered by an increase in UCP2 level. In INS-1 cells, a similar increase in UCP2 level did not modify glucose-induced insulin secretion, cytosolic ATP and ATP/ADP ratio, or glucose oxidation. Increased levels of UCP2 did not modify the mitochondrial membrane potential and oxygen consumption. Increased UCP2 levels decreased cytokine-induced production of reactive oxygen species. Conclusion/interpretation: The results obtained in transgenic mice and in the beta cell line do not support the hypothesis that an increase in UCP2 protein per se uncouples the mitochondria and decreases glucose-induced insulin secretion. In contrast, the observation that increased UCP2 levels decrease cytokine-induced production of reactive oxygen species indicates a potential protective effect of the protein on beta cells, as observed in other cell type

Adipose Tissue Plasticity During Catch-Up Fat Driven by Thrifty Metabolism: Relevance for Muscle-Adipose Glucose Redistribution During Catch-Up Growth

OBJECTIVE: Catch-up growth, a risk factor for later type 2 diabetes, is characterized by hyperinsulinemia, accelerated body-fat recovery (catch-up fat), and enhanced glucose utilization in adipose tissue. Our objective was to characterize the determinants of enhanced glucose utilization in adipose tissue during catch-up fat. RESEARCH DESIGN AND METHODS: White adipose tissue morphometry, lipogenic capacity, fatty acid composition, insulin signaling, in vivo glucose homeostasis, and insulinemic response to glucose were assessed in a rat model of semistarvation-refeeding. This model is characterized by glucose redistribution from skeletal muscle to adipose tissue during catch-up fat that results solely from suppressed thermogenesis (i.e., without hyperphagia). RESULTS: Adipose tissue recovery during the dynamic phase of catch-up fat is accompanied by increased adipocyte number with smaller diameter, increased expression of genes for adipogenesis and de novo lipogenesis, increased fatty acid synthase activity, increased proportion of saturated fatty acids in triglyceride (storage) fraction but not in phospholipid (membrane) fraction, and no impairment in insulin signaling. Furthermore, it is shown that hyperinsulinemia and enhanced adipose tissue de novo lipogenesis occur concomitantly and are very early events in catch-up fat. CONCLUSIONS: These findings suggest that increased adipose tissue insulin stimulation and consequential increase in intracellular glucose flux play an important role in initiating catch-up fat. Once activated, the machinery for lipogenesis and adipogenesis contribute to sustain an increased insulin-stimulated glucose flux toward fat storage. Such adipose tissue plasticity could play an active role in the thrifty metabolism that underlies glucose redistribution from skeletal muscle to adipose tissue

Peptide YY ablation in mice leads to the development of hyperinsulinaemia and obesity

Aims/hypothesis. Obese people exhibit reduced circulating peptide YY (PYY) levels, but it is unclear whether this is a consequence or cause of obesity. We therefore investigated the effect of Pyy ablation on energy homeostasis. Methods. Body composition, i.p. glucose tolerance, food intake and hypothalamic neuropeptide expression were determined in Pyy knock-out and wild-type mice on a normal or high-fat diet. Results. Pyy knock-out significantly increased bodyweight and increased fat mass by 50% in aged females on a normal diet. Male chow-fed Pyy −/− mice were resistant to obesity but became significantly fatter and glucose-intolerant compared with wild-types when fed a high-fat diet. Pyy knock-out animals exhibited significantly elevated fasting or glucose-stimulated serum insulin concentrations vs wild-types, with no increase in basal or fasting-induced food intake. Pyy knock-out decreased or had no effect on neuropeptide Y expression in the arcuate nucleus of the hypothalamus, and significantly increased proopiomelanocortin expression in this region. Male but not female knock-outs exhibited significantly increased growth hormone-releasing hormone expression in the ventromedial hypothalamus and significantly elevated serum IGF-I and testosterone levels. This sex difference in activation of the hypothalamo–pituitary somatotrophic axis by Pyy ablation may contribute to the resistance of chow-fed male knock-outs to late-onset obesity. Conclusions/interpretation. PYY signalling is important in the regulation of energy balance and glucose homeostasis, possibly via regulation of insulin release. Therefore reduced PYY levels may predispose to the development of obesity, particularly with ageing or under conditions of high-fat feeding

Susceptibility of Pancreatic Beta Cells to Fatty Acids Is Regulated by LXR/PPARα-Dependent Stearoyl-Coenzyme A Desaturase

Chronically elevated levels of fatty acids-FA can cause beta cell death in vitro. Beta cells vary in their individual susceptibility to FA-toxicity. Rat beta cells were previously shown to better resist FA-toxicity in conditions that increased triglyceride formation or mitochondrial and peroxisomal FA-oxidation, possibly reducing cytoplasmic levels of toxic FA-moieties. We now show that stearoyl-CoA desaturase-SCD is involved in this cytoprotective mechanism through its ability to transfer saturated FA into monounsaturated FA that are incorporated in lipids. In purified beta cells, SCD expression was induced by LXR- and PPARα-agonists, which were found to protect rat, mouse and human beta cells against palmitate toxicity. When their SCD was inhibited or silenced, the agonist-induced protection was also suppressed. A correlation between beta cell-SCD expression and susceptibility to palmitate was also found in beta cell preparations isolated from different rodent models. In mice with LXR-deletion (LXRβ-/- and LXRαβ-/-), beta cells presented a reduced SCD-expression as well as an increased susceptibility to palmitate-toxicity, which could not be counteracted by LXR or PPARα agonists. In Zucker fatty rats and in rats treated with the LXR-agonist TO1317, beta cells show an increased SCD-expression and lower palmitate-toxicity. In the normal rat beta cell population, the subpopulation with lower metabolic responsiveness to glucose exhibits a lower SCD1 expression and a higher susceptibility to palmitate toxicity. These data demonstrate that the beta cell susceptibility to saturated fatty acids can be reduced by stearoyl-coA desaturase, which upon stimulation by LXR and PPARα agonists favors their desaturation and subsequent incorporation in neutral lipids