Effects of subcutaneous, low-dose glucagon on insulin-induced mild hypoglycaemia in patients with insulin pump treated type 1 diabetes.

AIM: To investigate the dose-response relationship of subcutaneous (s.c.) glucagon administration on plasma glucose and on counter-regulatory hormone responses during s.c. insulin-induced mild hypoglycaemia in patients with type 1 diabetes treated with insulin pumps. METHODS: Eight insulin pump-treated patients completed a blinded, randomized, placebo-controlled study. Hypoglycaemia was induced in the fasting state by an s.c. insulin bolus and, when plasma glucose reached 3.4 mmol/l [95% confidence interval (CI) 3.2-3.5], an s.c. bolus of either 100, 200, 300 µg glucagon or saline was administered. Plasma glucose, counter-regulatory hormones, haemodynamic variables and side effects were measured throughout each study day. Peak plasma glucose level was the primary endpoint. RESULTS: Plasma glucose level increased significantly by a mean (95% CI) of 2.3 (1.7-3.0), 4.2 (3.5-4.8) and 5.0 (4.3-5.6) mmol/l to 6.1 (4.9-7.4), 7.9 (6.4-9.3) and 8.7 (7.8-9.5) vs 3.6 (3.4-3.9) mmol/l (p < 0.001) after the three different glucagon doses as compared with saline, and the increase was neither correlated with weight nor insulin levels. Area under the plasma glucose curve, peak plasma glucose, time to peak plasma glucose and duration of plasma glucose level above baseline were significantly enhanced with increasing glucagon doses; however, these were not significantly different between 200 and 300 µg glucagon. Free fatty acids and heart rates were significantly lower initially after glucagon than after saline injection. Other haemodynamic variables, counter-regulatory hormones and side effects did not differ between interventions. CONCLUSIONS: An s.c. low-dose glucagon bolus effectively restores plasma glucose after insulin overdosing. Further research is needed to investigate whether low-dose glucagon may be an alternative treatment to oral carbohydrate intake for mild hypoglycaemia in patients with type 1 diabetes.

Ectopic expression of RBP4 impairs the insulin pathway and inguinal fat deposition in mice

A large body of evidence has linked retinol-binding protein 4 (RBP4) to systemic insulin resistance, but little is known about its function in fat deposition. This study aimed to confirm the involvement of RBP4 in inguinal fat deposition and insulin by intraperitoneal injection of adenovirus-mediated RBP4 to mice. Intraperitoneal injection of adenoviral vectors was validated as an efficient gene manipulation tool for over-expressing recombinant proteins in vivo. Ectopic expression of RBP4 decelerated inguinal fat deposition by decreasing the size of adipocytes. Moreover, the introduction of exogenous RBP4 blunted the response of inguinal adipocytes to insulin signals. These findings suggest that RBP4 impaired in vivo adipogenesis, partly through the repression of the insulin pathway

Insulin/IGF-1 and TNF-alpha stimulate phosphorylation of IRS-1 at inhibitory Ser307 via distinct pathways.

Serine/threonine phosphorylation of IRS-1 might inhibit insulin signaling, but the relevant phosphorylation sites are difficult to identify in cultured cells and to validate in isolated tissues. Recently, we discovered that recombinant NH2-terminal Jun kinase phosphorylates IRS-1 at Ser307, which inhibits insulin-stimulated tyrosine phosphorylation of IRS-1. To monitor phosphorylation of Ser307 in various cell and tissue backgrounds, we prepared a phosphospecific polyclonal antibody designated alphapSer307. This antibody revealed that TNF-alpha, IGF-1, or insulin stimulated phosphorylation of IRS-1 at Ser307 in 3T3-L1 preadipocytes and adipocytes. Insulin injected into mice or rats also stimulated phosphorylation of Ser307 on IRS-1 immunoprecipitated from muscle; moreover, Ser307 was phosphorylated in human muscle during the hyperinsulinemic euglycemic clamp. Experiments in 3T3-L1 preadipocytes and adipocytes revealed that insulin-stimulated phosphorylation of Ser307 was inhibited by LY294002 or wortmannin, whereas TNF-alpha-stimulated phosphorylation was inhibited by PD98059. Thus, distinct kinase pathways might converge at Ser307 to mediate feedback or heterologous inhibition of IRS-1 signaling to counterregulate the insulin response.

Postnatal changes in the insulin-depleting action and disposition of cyproheptadine in rats.

The relationship between age-related differences in cyproheptadine (CPH)-induced alteration of endocrine pancreas function and the disposition of the drug was examined in this study. Various doses of CPH (5, 11, 22.5 or 45 mg/kg) were given orally once daily for 2 days to 10-, 15-, 25- and 50-day-old rats. Pancreatic and serum insulin measured 24 h after the second dose showed a drug-dependent decline, and the extent of this effect was dependent on the dose administered and the age of the animal. In 50-day-old rats, a significant reduction in pancreatic and serum insulin was detected only after high doses (22.5 and 45 mg/kg) of the drug. However, in 10- and 15-day-old rats, the effects were observed after the lowest dose (5 mg/kg). In separate experiments, the concentrations of CPH and its active metabolites, desmethylcyproheptadine (DMCPH), desmethylcyproheptadine-10,11-epoxide (DMCPH-epoxide) and cyproheptadine-10,11-epoxide (CPH-epoxide), were measured in the pancreas, liver and lung of neonatal and young rats at various times after the second dose of CPH (11 mg/kg). In the younger age groups (10- and 15-day-olds), there were significantly higher tissue levels of unchanged drug at all times examined. Certain of the drug metabolites known to be inhibitors of insulin synthesis had higher and/or more prolonged tissue concentrations in younger animals. For example, the metabolite CPH-epoxide was found only in tissues from younger age groups. Twenty-four hours after the second dose of CPH, no drug-derived product was present in tissues of 25- and 50-day-old rats, whereas significant amounts of DMCPH-epoxide, a potent CPH metabolite inhibiting insulin synthesis, was detected in the tissues of 10- and 15-day-old rats. The data show that there are age-related differences in the susceptibility of pancreatic B cells to the actions of CPH, and that these differences are associated with age-related changes in the disposition of the drug.