Dogfish pressor response to potassium blocked by magnesium and phentolamine.

In vivo infusion of MgCl2 blocks the dogfish pressor response to K+. This action of Mg2+ was contrasted to phentolamine in in vivo and in vitro experiments. Mg2+ blocks the spontaneous release of catecholamines from dogfish chromaffin tissue but does not alter the norepinephrine-induced contraction of the isolated dogfish artery. In vivo infusion of Mg2+ causes a significant decrease in resting catecholamine levels and diminishes the catecholamine release caused by K+ challenge. Both Mg2+ and phentolamine block the pressor action of K+, Mg2+ by preventing the K+-induced release of catecholamines and phentolamine by preventing the circulating catecholamines from interacting with alpha-adrenergic receptor sites.