Influence of peripheral and central administration of apomorphine and morphine on intragastric pressure in the dog.

Apomorphine was about 30 times more potent in inducing gastric relaxation when applied intracerebroventricularly (i.c.v.) than when injected intravenously (i.v.) in the conscious dog. In the anesthetized dog, the dose of apomorphine producing gastric relaxation via the vertebral artery was at least 10 times lower than that needed to produce gastric relaxation via the i.v. route. For morphine, similar doses had to be given i.c.v. and i.v. to obtain the same degree of gastric relaxation in the conscious dog; in the anesthetized dog, morphine was 3 times more potent via the vertebral artery than i.v. The results suggest that apomorphine-induced gastric relaxation in the dog is mediated via a central site located in the region supplied by the vertebral artery, but that the gastric relaxatory effect of morphine is mediated by both a peripheral and a central site of action.