Dopamine receptors in pancreatic acinar cells from dog.

Dispersed acini from dog pancreas were used to characterize dopamine receptors in a study on the stimulation of cellular cyclic AMP formation and the binding of [3H]dopamine. Dopamine elicited concentration-dependent stimulation of cellular cyclic AMP with a maximal increase occurring at a concentration of 0.1 mM (EC50 = 1 microM). Epinine produced a potent stimulation similar to that by dopamine; the alpha-adrenoceptor agonists (amidephrine and noradrenaline) were less potent. Isoproterenol and apomorphine were ineffective. The effect of dopamine was potently blocked by dopamine receptor antagonists such as cis-(Z)-flupenthixol, haloperidol, fluphenazine, whereas spiperone, sulpiride and domperidone were weakly active. Apomorphine acted as an antagonist to inhibit dopamine-stimulated cellular cyclic AMP formation as well as phenoxybenzamine. Yohimbine, prazosin or clonidine were poorly or not active. The affinity of agents to stimulate cellular cyclic AMP formation or to inhibit dopamine-stimulated cellular cyclic AMP formation was closely related to their affinity to inhibit the binding of [3H]dopamine to pancreatic acini, providing evidence that dopamine binding sites are receptors that mediate the action of dopamine on cAMP accumulation. This was further substantiated by the demonstration of specific binding sites for [3H]cis-(Z)-flupenthixol.