Inhibition of catecholamine release by alpha-adrenergic activation: Interaction with Na, K-ATPase

In rat adrenal gland incubated in vitro, phenylephrine and naphazoline inhibited the release of catecholamines (CA) induced in a medium containing K⁺ (5.6 mM). In K⁺-free medium or in the presence of ouabain (10^-3 M) phenylephrine and naphazoline had no effect on CA release. The α-adrenergic blockers, phentolamine and phenoxybenzamine, increased CA release in a K⁺-medium but had no effect on CA release from adrenal medulla in a K⁺-free or ouabain (10^-3 M) containing medium. PGE₂ inhibited the release of CA both in the presence and in the absence of K⁺, as well as in the presence of ouabain (10^-3 M). Activation of α-adrenergic receptors in the adrenal medulla by phenylephrine and naphazoline resulted in increased Na, K-ATPase activity but no effect on Mg-ATPase. PGE₂ acts through a different mechanism.