Two mechanisms of isoproterenol inhibition of smooth muscle.

The relaxation of depolarized ideal and uterine smooth muscle by isoproterenol was compared with that brought about by dibutyryl-cAMP and by other agents which increase cytoplasmic cAMP. Qualitative differences observed between the time courses of the relaxations imply the existence of a rapid beta-adrenergic mechanism independent of cAMP as well as a slower cAMP-dependent relaxation. This dual process model for beta-adrenergic inhibition of smooth muscle is consistent with seemingly opposing published reports.