The effect of carvedilol on blood glucose levels in normal albino rats

Carvedilol improves glucose tolerance and insulin sensitivity in treatment of adrenergic overdrive in high fat diet-induced obesity in mice

Catecholamine excess reflecting an adrenergic overdrive of the sympathetic nervous system (SNS) has been proposed to link to hyperleptinemia in obesity and may contribute to the development of metabolic disorders. However, relationship between the catecholamine level and plasma leptin in obesity has not yet been investigated. Moreover, whether pharmacological blockade of the adrenergic overdrive in obesity by the third-generation beta-blocker agents such as carvedilol could help to prevent metabolic disorders is controversial and remains to be determined. Using the high fat diet (HFD)-induced obese mouse model, we found that basal plasma norepinephrine, the principal catecholamine as an index of SNS activity, was persistently elevated and highly correlated with plasma leptin concentration during obesity development. Targeting the adrenergic overdrive from this chronic norepinephrine excess in HFD-induced obesity with carvedilol, a third-generation beta-blocker with vasodilating action, blunted the HFD-induced hepatic glucose over-production by suppressing the induction of gluconeogenic enzymes, and enhanced the muscular insulin signaling pathway. Furthermore, carvedilol treatment in HFD-induced obese mice decreased the enlargement of white adipose tissue and improved the glucose tolerance and insulin sensitivity without affecting body weight and blood glucose levels. Our results suggested that catecholamine excess in obesity might directly link to the hyperleptinemic condition and the therapeutic targeting of chronic adrenergic overdrive in obesity with carvedilol might be helpful to attenuate obesity-related metabolic disorders.

Improvement in glycemia after glucose or insulin overload in leptin-infused rats is associated with insulin-related activation of hepatic glucose metabolism

Background

Insulin regulates glucose homeostasis through direct effects on the liver, among other organs, with leptin modulating insulin’s hepatic actions. Since central leptin may modify insulin signaling in the liver, we hypothesized that leptin infusion activates hepatic glycogen synthesis following peripheral administration of a bolus of glucose or insulin, thus regulating glycemia.

Findings

Oral glucose and intraperitoneal insulin tolerance tests were performed in control, intracerebroventricular leptin-treated and pair-fed rats during 14 days. An improvement in glycemia and an increase in hepatic free glucose and glycogen concentrations after glucose or insulin overload were observed in leptin-treated rats. In order to analyze whether the liver was involved in these changes, we studied activation of insulin signaling by Western blotting and multiplex bead immunoassay after leptin infusion. Our studies revealed an increase in phosphorylation of insulin receptor substrate-1 and Akt in leptin-treated rats. Examination of parameters related to glucose uptake and metabolism in the liver revealed an augment in glucose transporter 2 and a decrease in phosphoenolpyruvate carboxylase protein levels in this group.

Conclusions

These results indicate that central leptin increases hepatic insulin signaling, associated with increased glycogen concentrations after glucose or insulin overload, leading to an improvement in glycemia.