Arterial smooth muscle effects of aldosterone and vasopressin: action on ionic fluxes.

We have shown previously that aldosterone injected s.c. to adrenalectomized rats has a mineralocorticoid specific action on the transmembrane movements of sodium and potassium from the rat tail artery. These effects appeared to be partly due to an unknown humoral factor. Indeed, the late in vivo effects of aldosterone on 22Na and 86Rb effluxes are suppressed or reduced after in vitro exposure to the hormone. In rats perfused with a specific antagonist of the pressor effect of vasopressin, the in vitro administration of aldosterone induced a kinetic action similar to that observed after in vitro exposure to the mineralocorticoid. Vasopressin exerts a direct action on 22Na and 86Rb effluxes. These effects were correlated in the time with the late in vivo effects of aldosterone. Moreover, vasopressin appears to potentiate the in vitro effects of aldosterone on 22Na and 86Rb effluxes. It is not yet possible to ascertain if this effect is additive or permissive.