Ripglut1;glut2 -/-mice have no endogenous glucose transporter type 2 (glut2) gene expression but rescue glucoseregulated insulin secretion. Control of glucagon plasma levels is, however, abnormal, with fed hyperglucagonemia and insensitivity to physiological hypo-or hyperglycemia, indicating that GLUT2-dependent sensors control glucagon secretion. Here, we evaluated whether these sensors were located centrally and whether GLUT2 was expressed in glial cells or in neurons. We showed that ripglut1;glut2 -/-mice failed to increase plasma glucagon levels following glucoprivation induced either by i.p. or intracerebroventricular 2-deoxy-D-glucose injections. This was accompanied by failure of 2-deoxy-D-glucose injections to activate c-Fos-like immunoreactivity in the nucleus of the tractus solitarius and the dorsal motor nucleus of the vagus. When glut2 was expressed by transgenesis in glial cells but not in neurons of ripglut1;glut2 -/-mice, stimulated glucagon secretion was restored as was c-Fos-like immunoreactive labeling in the brainstem. When ripglut1;glut2 -/-mice were backcrossed into the C57BL/6 genetic background, fed plasma glucagon levels were also elevated due to abnormal autonomic input to the a cells; glucagon secretion was, however, stimulated by hypoglycemic stimuli to levels similar to those in control mice. These studies identify the existence of central glucose sensors requiring glut2 expression in glial cells and therefore functional coupling between glial cells and neurons. These sensors may be activated at different glycemic levels depending on the genetic background.

The role of the gluco-incretin hormones GIP and GLP-1 in the control of β cell function was studied by analyzing mice with inactivation of each of these hormone receptor genes, or both. Our results demonstrate that glucose intolerance was additively increased during oral glucose absorption when both receptors were inactivated. After intraperitoneal injections, glucose intolerance was more severe in double-as compared to single-receptor KO mice, and euglycemic clamps revealed normal insulin sensitivity, suggesting a defect in insulin secretion. When assessed in vivo or in perfused pancreas, insulin secretion showed a lack of first phase in Glp-1R -/-but not in Gipr -/-mice. In perifusion experiments, however, first-phase insulin secretion was present in both types of islets. In double-KO islets, kinetics of insulin secretion was normal, but its amplitude was reduced by about 50% because of a defect distal to plasma membrane depolarization. Thus, gluco-incretin hormones control insulin secretion (a) by an acute insulinotropic effect on β cells after oral glucose absorption (b) through the regulation, by GLP-1, of in vivo first-phase insulin secretion, probably by an action on extra-islet glucose sensors, and (c) by preserving the function of the secretory pathway, as evidenced by a β cell autonomous secretion defect when both receptors are inactivated.

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OBJECTIVE-Recent observations indicate that the delivery of nitric oxide by endothelial nitric oxide synthase (eNOS) is not only critical for metabolic homeostasis, but could also be important for mitochondrial biogenesis, a key organelle for free fatty acid (FFA) oxidation and energy production. Because mice deficient for the gene of eNOS (eNOS Ϫ/Ϫ ) have increased triglycerides and FFA levels, in addition to hypertension and insulin resistance, we hypothesized that these knockout mice may have decreased energy expenditure and defective ␤-oxidation.RESEARCH DESIGN AND METHODS-Several markers of mitochondrial activity were assessed in C57BL/6J wild-type or eNOS Ϫ/Ϫ mice including the energy expenditure and oxygen consumption by indirect calorimetry, in vitro ␤-oxidation in isolated mitochondria from skeletal muscle, and expression of genes involved in fatty acid oxidation. RESULTS-eNOSϪ/Ϫ mice had markedly lower energy expenditure (Ϫ10%, P Ͻ 0.05) and oxygen consumption (Ϫ15%, P Ͻ 0.05) than control mice. This was associated with a roughly 30% decrease of the mitochondria content (P Ͻ 0.05) and, most importantly, with mitochondrial dysfunction, as evidenced by a markedly lower ␤-oxidation of subsarcolemmal mitochondria in skeletal muscle (Ϫ30%, P Ͻ 0.05). Finally, impaired mitochondrial ␤-oxidation was associated with a significant increase of the intramyocellular lipid content (30%, P Ͻ 0.05) in gastrocnemius muscle. CONCLUSIONS-These data indicate that elevated FFA and triglyceride in eNOSϪ/Ϫ mice result in defective mitochondrial ␤-oxidation in muscle cells. Diabetes

The role of the gluco-incretin hormones GIP and GLP-1 in the control of β cell function was studied by analyzing mice with inactivation of each of these hormone receptor genes, or both. Our results demonstrate that glucose intolerance was additively increased during oral glucose absorption when both receptors were inactivated. After intraperitoneal injections, glucose intolerance was more severe in double-as compared to single-receptor KO mice, and euglycemic clamps revealed normal insulin sensitivity, suggesting a defect in insulin secretion. When assessed in vivo or in perfused pancreas, insulin secretion showed a lack of first phase in Glp-1R -/-but not in Gipr -/-mice. In perifusion experiments, however, first-phase insulin secretion was present in both types of islets. In double-KO islets, kinetics of insulin secretion was normal, but its amplitude was reduced by about 50% because of a defect distal to plasma membrane depolarization. Thus, gluco-incretin hormones control insulin secretion (a) by an acute insulinotropic effect on β cells after oral glucose absorption (b) through the regulation, by GLP-1, of in vivo first-phase insulin secretion, probably by an action on extra-islet glucose sensors, and (c) by preserving the function of the secretory pathway, as evidenced by a β cell autonomous secretion defect when both receptors are inactivated.

TE supplementation was associated with an increased skin tissue content of selenium and zinc and with a reduction in skin protein catabolism.

Fatty acid transporter protein (FATP)-1 mRNA expression was investigated in skeletal muscle and in subcutaneous abdominal adipose tissue of 17 healthy lean, 13 nondiabetic obese, and 16 obese type 2 diabetic subjects. In muscle, FATP-1 mRNA levels were higher in lean women than in lean men (2.2 +/- 0.1 vs. 0.6 +/- 0.2 amol/microg total RNA, P < 0.01). FATP-1 mRNA expression was decreased in skeletal muscle in obese women both in nondiabetic and in type 2 diabetic patients (P < 0.02 vs. lean women in both groups), and in all women there was a negative correlation with basal FATP-1 mRNA level and body mass index (r = -0.74, P < 0.02). In men, FATP-1 mRNA was expressed at similar levels in the three groups both in skeletal muscle (0.6 +/- 0.2, 0.6 +/- 0.2, and 0.8 +/- 0.2 amol/microg total RNA in lean, obese, and type 2 diabetic male subjects) and in adipose tissue (0.9 +/- 0.2 amol/microg total RNA in the 3 groups). Insulin infusion (3 h) reduced FATP-1 mRNA levels in muscle in lean women but not in lean men. Insulin did not affect FATP-1 mRNA expression in skeletal muscle in obese nondiabetic or in type 2 diabetic subjects nor in subcutaneous adipose tissue in any of the three groups. These data show a gender-related difference in the expression of the fatty acid transporter FATP-1 in skeletal muscle of lean individuals and suggest that changes in FATP-1 expression may not contribute to a large extent to the alterations in fatty acid uptake in obesity and/or type 2 diabetes.

The metabolic fate of an oral long-chain-triacylglycerol (LCT) load and of a mixed oral LCT and medium-chain-triacylglycerol (MCT) load was followed for 6 h in eight control and eight obese subjects with normal postabsorptive triacylglycerol concentrations. Labeled triacylglycerol and indirect calorimetry were used. Results showed that LCTs were less oxidized in obese than in control subjects (3.2+/-0.5 compared with 6.0+/-0.4 g, P < 0.01). Moreover, the amount of LCT oxidized was negatively correlated with fat mass (r = -0.77, P < 0.01). Appearance in plasma of dietary triacyglycerol-derived long-chain fatty acids was blunted in obese subjects and it was negatively related to fat mass (r = -0.84, P < 0.01) and positively to LCT oxidation (r = 0.70, P < 0.01). On the contrary, MCT oxidation was not altered in obese subjects compared with control subjects. Furthermore, the proportion of MCTs oxidized was higher in both groups compared with LCTs (x+/-SEM: 57.5+/-2.6% compared with 15.2+/-1.6%, P < 0.01, n = 16). Our conclusion is that obesity is associated with a defect in the oxidation of dietary LCTs probably related to an excessive uptake by the adipose tissue of meal-derived long-chain fatty acids. MCTs, the oxidation of which is not altered in obesity, could therefore be of interest in the dietary treatment of obesity.