Effects of endocannabinoid (CB1) receptor antagonism on insulin resistance in a rodent model of metabolic syndrome

The endocannabinoid system is a novel pharmacological target in the treatment of metabolic syndrome. Antagonism of the endocannabinoid-1 receptor (CB1R) leads to a transient reduction in food intake, a sustained decrease in body weight and an improvement in metabolic parameters in animal models of obesity. Skeletal muscle is the primary tissue involved in glucose uptake in response to insulin, and insulin sensitivity of skeletal muscle is vital to the maintenance of whole-body euglycemia. Little is known regarding the effects of CB1R antagonism on skeletal muscle glucose transport activity. The purpose of this dissertation was to test the hypothesis that antagonism of the CB1R activates signaling molecules of the insulin signaling pathway to increase glucose transport activity in normal and insulin-resistant skeletal muscle, thereby improving whole-body glucose tolerance. CB1R antagonism with SR141716 directly enhanced basal and insulin-stimulated glucose transport activity in skeletal muscle from lean and obese Zucker while activation of the CB1R with ACEA, decreased glucose transport activity. Key proteins associated with regulation of glucose transport activity were not altered by either CB1R agonism (ACEA) or antagonism (SR141716). Chronic CB1R antagonist treatment (10 mg/kg SR141716 i.p. / 14 days) also enhanced insulin-stimulated glucose transport activity in skeletal muscle of both lean and obese animals, again with no alteration in relevant signaling factors. Plasma free fatty acids (FFAs) were decreased in chronically-treated lean and obese animals and whole-body insulin sensitivity was improved in obese Zucker rats. The enhanced insulin sensitivity seen in chronically-treated obese animals was associated with a dramatic reduction in insulin secretion following a glucose challenge. Acute CB1R antagonism in obese animals also elicited a reduction in insulin secretion following a glucose challenge; however, with no improvement of whole-body insulin sensitivity. Acute CB1R antagonist treatment did not alter skeletal muscle glucose transport activity or circulating FFAs for any animals. These data suggest that although CB1R antagonism directly enhances basal and insulin stimulated glucose transport in skeletal muscle of lean and obese rats, direct action on the skeletal muscle is not responsible for the improvement in insulin-stimulated glucose transport activity and whole-body insulin sensitivity seen in chronically-treated obese animals