cAMP levels and alpha and beta receptors stimulation by noradrenaline in frog skin.

The effect of noradrenaline on intracellular levels of cAMP in epithelial cells isolated from frog skin, has been studied both in the presence and in the absence of alpha (phentolamine) or beta (propranolol) adrenergic blocking agents. Such levels are increased by hormonal treatment and are linked to the stimulation of beta-adrenergic receptors, while alpha-stimulation has an inhibitory effect. Higher levels of cAMP are reached in the presence of both Ca2+ and Mg2+, confirming the existence of a Ca2+ and Mg2+-dependent adenyl-cyclase, stimulated by noradrenaline. The experimental conditions necessary to induce the highest intracellular cAMP levels, are those in which the permeabilizing effect reaches its maximum.