Involvement of capsaicin-sensitive nerves in the regulation of glucose tolerance in diabetic rats

The role of afferent sensory nerves in glucose tolerance and glucose stimulated insulin secretion was investigated in normal (N) or neonatal streptozotocin-induced diabetic (D) rats treated with capsaicin (NC and DC, respectively) during the neonatal period. In capsaicin treated animals, oral glucose tolerance was markedly improved both in NC and DC whereas insulin secretion was not affected. The effect of alpha 2-adrenergic blockade was investigated in D and DC rats. The alpha 2-adrenoceptor antagonist deriglidole (3 mg/kg i.p.) administered 30 min before glucose load slightly reduced glucose levels and markedly increased insulin levels both in D and DC rats. Thereafter, the high insulin levels were maintained or further increased following glucose administration. As a consequence, glucose tolerance was further improved in D and in DC, which already expressed an improved glucose tolerance after capsaicin administration. These results suggest that sensory nerves are implicated in the control of glucose tolerance in normal and neonatal streptozotocin-induced diabetic rats through a mechanism independent of insulin release. It is also suggested that afferent sensory nerves are not implicated in the adrenergic control of insulin secretion from pancreatic beta-cells.