Reduction of hypoxic pulmonary vasoconstriction by magnesium chloride.

Abstract

Since parenterally administered Mg salts relax constricted systemic blood vessels, perhaps intravenous infusions of MgCl2 reduce hypoxia-induced pulmonary vasoconstriction. Ten anesthetized dogs developed typical increases in mean pulmonary artery pressure (Ppa) and total pulmonary resistance (TPR) at normal plasma concentrations [Mg]pl whenthey breathed 10% O2 [after 100% O2]. Ppa rose from 14.4 (10.70 SE) to 29.6 ([plus or minus].2.39)mmHg, and TPR from 0.12 ([plus or minus]0.012) to 0.18 ([plus or minus]0.020) mm Hg/((ml/min)/kg); these increases were statistically significant (P 0.001). When [Mg]p1 was raised in a stepwise manner by infusions of isotonic MgCl2, the increases in Ppa and TPR in response to hypoxia lessened so that at [Mg]p1 of 9-12 meq/l, the Ppa rose only 6.9 mm Hg (compared to 15.2 mm Hg at normal [Mg]pl), and the TPR did not rise at all. Elevations of [Mg]pl to 9-12 meq/1. had no undesirable effects on cardiac output, total systemic resistance, aortic pressure, or pulmonary ventilation. Acute increases in total [Mg]pl to 9-12 meq/1. lessened or blocked the hypoxia-induced active pulmonary vasoconstriction without depressing other cardiovascular and ventilatory responses to hypoxia.