MAGNESIUM IS ESSENTIAL IN MECHANISMS OF PULMONARY VASOMOTOR CONTROL

Magnesium (Mg2+) is an important cofactor in many intracellular bioche mical reactions; however, its role in the signal transduction pathways of pulmonary vascular smooth muscle is poorly defined, The purpose of this study was to examine the following mechanisms of pulmonary vascu lar smooth relaxation in the presence and in the absence of Mg2+: (1) Endothelium-dependent cGMP-mediated relaxation (response to acetylchol ine, ACh), (2) Endothelium-independent cGMP-mediated relaxation (respo nse to sodium nitroprusside, SNP), and (3) beta(2)-adrenergic cAMP-med iated relaxation (response to isoproterenol, ISO). Dose response curve s were generated in isolated rat pulmonary artery rings preconstricted with phenylephrine. With Mg2+, ACh 10(-6) M produced complete ring re laxation but in the absence of Mg2+, only 66% relaxation was produced in response to ACh 10(-6) M (P < 0.05). On the other hand, endothelium -independent cGMP-mediated relaxation (response SNP) was not impaired without Mg2+. beta(2)-adrenergic cAMP-mediated relaxation was also imp aired in the absence of Mg2+. In the presence of Mg2+, ISO 10(-6) M pr oduced complete relaxation but without Mg2+, only 30% relaxation was p roduced (P < 0.05). We conclude that Mg2+ is essential for cGMP- and c AMP-mediated mechanisms of pulmonary vasorelaxation. Hypomagnesemia sh ould be avoided to prevent pulmonary vasomotor dysfunction. (C) 1996 A cademic Press, Inc.