Atrial natriuretic factor enhances the hydroosmotic response of toad bladder to submaximal doses of vasopressin

Using the toad urinary bladder, we examined the effects of submaximal levels of atrial natriuretic factor (ANF) upon the hydroosmotic water flux caused by physiologic concentrations of vasopressin (VP). Pretreatment with ANF prior to the addition of VP (10(-9)M) significantly enhanced water transport (123 +/- 23%) compared to tissues exposed to VP alone. Pre-treatment with ANF also significantly enhanced the hydroosmotic response (143 +/- 43%) to cyclic-3',5'-adenosine monophosphate (cyclic-AMP). When the concentration of VP was progressively increased during time course experiments, an inhibitory effect of ANF on water transport followed the early stimulatory response to this peptide. The data support a novel, dose-dependent modulatory role for ANF early in the response of transporting epithelia to VP. Moreover, the stimulatory effect of submaximal doses of ANF to cyclic-AMP mediated water transport suggest the possibility that modulation by ANF may occur at a site following the VP receptor-linked adenylate cyclase system.