INHIBITION BY DOPAMINE OF THE HYDROOSMOTIC RESPONSE (WATER TRANSFER) OF THE TOAD BLADDER TO VASOPRESSIN

¹ Departments of Pharmacology and Ophthalmology, Mt. Sinai School of Medicine of the City University of New York, New York

Dopamine (10^-7 M) competitively decreased the hydro-osmotic response of the toad urinary bladder to vasopressin. Norepinephrine and epinephrine also decreased the effect of vasopressin but isoproterenol (10^-4 M) was much less active. None of the catecholamines influenced the osmotic permeability of the bladder in time absence of vasopressin. The hydro-osmotie action of cyclic adenosine monophosphate was unaffected by dopamine (10^-4 M) but that of theophylline (20 mM) was abolished. Either alpha or beta adrenergic blockers (phentolamine or propanolol) abolished time antagonism of dopamine to vasopressin. In contrast only phentolamine could reduce this action of norepinephrine. It is suggested that dopamine competitively antagonizes the effect of vasopressin possibly on adenyl cyclase.