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+ (5.6mM). In K+-free medium or in the presence of ouabain (10(-3) M) phenylephrine and naphazoline had no effect on CA release. The alpha-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 alpha-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.