DOPAMINE SLOWS ROD PHAGOCYTOSIS BY THE BO VINE RETINAL-PIGMENT EPITHELIUM IN-VITRO THROUGH A D-1 RECEPTOR

Photoreceptor disc shedding and their phagocytosis by the retinal pigm ent epithelium undergo a daily rhythm entrained by an intrinsic oscill ator involving melatonin and dopamine in non-mammals. Such a mechanism is not demonstrated in mammals, but the rhythm of photoreceptor renew al ran be modulated by exogenous melatonin and dopamine. The present e xperiments were designed to show whether a direct action of DA occurs on pigment epithelial cells, and to identify the receptor mediating th is action. Primary cultures of bovine retinal pigment epithelium were incubated with bovine rod outer segments in the presence of dopamine, D-1 and D-2 agonists, D-1 antagonist and forskolin. Dopamine, D-1 agon ist and forskolin decreased phagocytosis, while D-2 agonist was inacti ve. Thus dopamine slows pigment epithelium phagocytosis in vitro throu gh a D-1 receptor. Increased phagocytosis following blockade of the re ceptor by an antagonist suggests a more complex modulation of phagocyt osis by dopamine.