Effect of apomorphine on peripheral venous gastrin and insulin levels in conscious dogs

Apomorphine 0.001, 0.005, 0.05 and 0.1 mg/kg were given i. v. to conscious dogs and gastrin and insulin levels were measured in peripheral venous blood. The lowest dose of apomorphine (0.001 mg/kg) did not change gastrin levels but some times caused a decrease of insulin levels, whereas the higher doses (0.005–0.1 mg/kg) induced a dose dependent increase of both hormone levels. The peak shaped release responses appeared within a few minutes and the basal values were reached again within 20 to 30 min. Apomorphine within the dose range which induced a response of insulin and gastrin also caused nausea and vomiting. Añer pretreatment with haloperidol (0.1 mg/kg) no signs of sickness were observed and the response of gastrin to 0.01 and 0.05 mg/kg of apomorphine was almost completely blocked, whereas the insulin response to both these doses was inhibited to ?50%. We conclude that the release of gastrin and insulin can be activated by stimulation of dopaminergic receptors, the anatomical location of which is not clear. Possible sites for the dopaminergic receptors are the hypothalamic region or the vagal centres in the medulla oblongata.