TYRAMINE CATECHOLAMINES AND ACTION OF VASOPRESSIN ON STIMULATION OF WATER EFFLUX IN TOAD BLADDERS

Both vasopressin and adenosine-3′,5-monophosphate enhance the rate of water translocation through the walls of toad bladders. Dichloroisoproterenol, epinephrine, and several related compounds antagonize this action of vasopressin but have little influence on the activity of adenosine-3′,5′-monophosphate. Tyramine also exerts a vasopressin-like effect on toad bladders which, like vasopressin, is antagonized by dichloroisoproterenol. In addition, tyramine overcomes the inhibition of vasopressin action exerted by dichloroisoproterenol. It is suggested that vasopressin acts via stimulation of adenyl cyclase, and that this stimulation may require the presence of tyramine or a closely related compound as a cofactor that can be displaced by dichloroisoproterenol, epinephrine, and several other structurally related compounds. © 1969.