Effects of catecholamines and their inhibitors on the isolated canine pancreas. II. Dopamine.

Dopaminergic agonists (dopamine, 2, 10, 50, and 250 mug; apomorphine, 1 mg; noradrenaline, 2, 20, and 200 mug), and inhibitors (haloperidol, 5 mg; pentamethonium, 500 mg; phenoxybenzamine, 15 mg, and atropine sulfate, 10 mg), were tested on isolated perfused canine pancreas; under basal conditions and under stimulation by a background of secretin (0.1, 0.5, and 10.0 clinical unit per hr), or of caerulein (1200 ng per hr). Low doses of dopamine induced a vasodilation inhibited by haloperidol Large doses induced a vasoconstriction, presumably by stimulation of alpha adrenergic receptors. Dopamine stimulated hydrelatic secretion. The calculated maximal response was about one-half that of secretin. This response was inhibited by haloperidol but not by atropine, pentamethonium, and phenoxybenzamine. No acinar degranulation was observed after stimulation by dopamine. The response to secretin was not altered by haloperidol. It was concluded that blood vessels and pancreatic tissue contain specific receptors to dopamine different from secretin receptors. Secretory response to noradrenaline after phenoxy benzamine was inhibited by haloperidol, suggesting that this effect was mediated by the stimulation of dopamine receptors of the cells. A hypothetical representation of the interrelation between dopamine, secretin, and noradrenaline is discussed.