| Abstract: | The effects of somatostatin on plasma concentrations of insulin and glucose in the presence of the selective alpha 1-adrenoceptor blocking agent prazosin or the selective alpha 2-adrenoceptor blocking drug yohimbine were studied in vivo in anesthetized rats. Infusion of both prazosin (0.080 mg/min) and yohimbine (0.018 mg/min) increased plasma insulin levels within 10 min. Prazosin, but not yohimbine, caused a significant increment in plasma glucose concentrations during the infusion of both prazosin and yohimbine, suggesting that the inhibitory effect of somatostatin is not mediated via a direct action on alpha 1- or alpha 2-adrenoceptors. Plasma glucose concentration fell slightly during somatostatin administration. A marked increment in insulin release occurred in response to cessation of the somatostatin infusion, both during prazosin- and yohimbine-treatment. We conclude that somatostatin efficiently inhibits insulin secretion during selective alpha 1- and alpha 2-adrenoceptor blockade and, further, that the insulin off-response after somatostatin treatment is potentiated by alpha-adrenoceptor blockade. This study also indicates that blockade of alpha 1- as well as alpha 2-adrenoceptors leads to an increased insulin secretion. |
