Comparative effects of morphine and cyclazocine on gastrointestinal motility in conscious dogs

The effects of intravenous (i.v.) and intracerebroventricular (i.c.v.) administration of two opiate-like drugs, morphine and cyclazocine on gastrointestinal motility were investigated in conscious fasted dogs chronically fitted with strain gauge transducers on the antrum, the jejunum and the colon. Intravenous administration of morphine (100 micrograms.kg-1) induced a disorganization of the cyclic motility of the antrum, a premature phase of regular activity on the jejunum and a stimulation of colonic motility. Intracerebroventricular administration of morphine at a 10 times lower dose induced a short (10-15 min) stimulation of gastric motility followed by a prolonged (2-3 hr) inhibition associated with a disorganization of the jejunal motility and a stimulation of colonic motility. Cyclazocine at the same doses (10 micrograms.kg-1) induced identical effects after administration by i.v. and i.c.v. routes which consisted of an inhibition of gastric and jejunal motility and a stimulation of colonic motility. These results show peculiar motor responses, at each level of the digestive tract, to central and peripheral administration of an opiate-like drug.