The Blocking Effect of Magnesium on the Secretion of Adrenal Catecholamines Induced by the Omission of Sodium from the Extracellular Medium

Abstract

The blocking action of Mg⁺⁺ on catecholamine release induced by the substitution of extracellular Na⁺ by an osmotic equivalent amount of sucrose was studied in isolated, perfused bovine adrenal glands. Perfusing glands with 10 mM Mg⁺⁺ produced at 51.1% inhibition on catecholamine release evoked by Na⁺ omission. Increasing the concentration of Mg⁺⁺ to 20 mM this inhibitory effect was enhanced to 90.3%. D-600 (0.3 mM) promoted a marked blockade of acetylcholine-induced release of catechol hormones that was partially and significantly reverted increasing the concentration of Ca⁺⁺ in the perfusion medium. D-600 (0.3 mM) failed to inhibit the catecholamine-releasing effect of Na⁺ deprivation. In adrenal glands previously perfused with D-600 (0.3 mM) and then exposed to a Locke solution containing D-600 (0.3 mM) + Mg⁺⁺ (10 or 20 mM) the inhibition of the secretory responses evoked by the omission of Na⁺ was of the same magnitude as that obtained when the glands were perfused with Mg⁺⁺ (10 or 20 mM) in the absence of D-600. These results are compatible with the view that the blocking effect of Mg⁺⁺ may involve an intracellular site of action and that the access of Mg⁺⁺ into the chromaffin cell may not be mediated through the Ca⁺⁺ channels.

Key words

Secretion of Catecholamines - Adrenal Medulla - Na⁺ Deprivation - Mg ⁺⁺ - D-600 - Acetylcholine - Ca⁺⁺ Channels