B cell adrenoceptors and sulphonylurea-induced insulin release in mouse islets.

Interactions of tolbutamide and glibenclamide with B cell adrenoceptors have been reported. This study evaluated the possible role of such interactions in the stimulation of insulin release. Mouse islets were incubated in the presence of 10 mmol/l glucose alone or with tolbutamide (10 mumol/l) or glibenclamide (0.02 mumol/l). At 0.01-10 mumol/l, blockers of alpha 2-adrenoceptors (yohimbine, idazoxan) or alpha 1-adrenoceptors (prazosin) had practically no effect on glucose-induced insulin release and did not affect its potentiation by sulphonylureas, except for a slight increase by 10 mumol/l prazosin and idazoxan. Nonspecific alpha-blockers (phentolamine, dihydroergotamine) increased control release at 10 mumol/l, but only the latter amplified the response to tolbutamide. Blockers of beta-adrenoceptors were tested at 0.1-100 mumol/l: propranolol (beta 1, beta 2), metoprolol (beta 1) and compound ICI 118-551 (beta 2). They increased glucose-induced insulin release at 100 mumol/l but variably altered the effect of sulphonylureas. Blockers of adrenoceptors have, thus, no effect on insulin release in vitro at therapeutic concentrations. At high concentrations, they non-specifically affect the action of sulphonylureas. We conclude that an interaction with B cell adrenoceptors is not involved in the insulinotropic action of sulphonylureas.