Dopaminergic Mechanisms in the Teleost Retina

Abstract

A specific dopamine-sensitive adenylate cyclase was identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 .mu.M-dopamine resulted in a 5- to 10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 .mu.M. l-Noradrenaline [norepinephrine] and l-adrenaline [epinephrine] were some 10 .times. less potent than dopamine; the .alpha.- and .beta.-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity; various ergot alkaloids [.beta.-ergocryptine, ergonovine, lysergic acid diethylamide lergotrile, lisuride and bromocryptine] produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonized by various neuroleptoic drugs including fluphenazine, .alpha.-flupenthixol and .alpha.-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with .alpha.- and .beta.-adrenoreceptor blocking agents, phenotlamine and propranolol, respectively, were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. A highly specific dopamine-sensitive adenylate cyclase apparently in present in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the ammmalian CNS.