Effects of galanin and norepinephrine on insulin secretion in the mouse

Galanin and norepinephrine (NE) both occur in adrenergic nerves in the pancreas. Since they are co-released from the nerve terminals and both inhibit glucose-induced insulin release, we investigated in the mouse if they cooperate in exerting this effect. When administered alone in vivo, both galanin (50-530 pmol/kg) and NE (40-320 nmol/kg) dose-dependently inhibited the increase in plasma insulin levels at 1 min following intravenous injection of glucose (2.8 mmol/kg). When galanin and NE were given together at different dose levels, no potentiating effect on the inhibition of the glucose-induced plasma insulin response was observed. In vitro, in overnight cultured mouse islets, both galanin (10(-9)-10(-6) M) and NE (10(-9)-10(-6) M) in a dose-related manner inhibited the insulin release induced by 11.1 mM glucose. Galanin (10(-9) M) did not further enhance the inhibited insulin response evoked by NE (10(-9)-10(-6) M). Thus, no functional evidence exists, either in vivo or in vitro, that galanin and NE potentiate the inhibitory action of each other on glucose-induced insulin release in the mouse.