Vasomotor effects of magnesium: a comparison with nifedipine and verapamil of in vitro reactivity in feline cerebral and peripheral arteries.

The vasomotor effects of magnesium ions and the calcium entry blockers nifedipine and verapamil have been studied in isolated feline cerebral, coronary and femoral arteries preconstricted by 124 mM potassium or 3 microM prostaglandin F2 alpha (PGF2 alpha). The order of potency for eliciting relaxation was: nifedipine greater than verapamil greater than magnesium. Magnesium showed the same profile of action as the calcium entry blockers in cerebral and coronary arteries, while the maximum relaxation obtained by magnesium was significantly smaller in femoral arteries constricted by potassium as compared with that of nifedipine (p less than 0.001) and verapamil (p less than 0.01). Besides this relaxant effect, magnesium was found to act as a constrictor during certain conditions; addition of magnesium to femoral arteries which had been preconstricted by PGF2 alpha in a magnesium-free solution resulted in relaxation in low concentrations and contraction at higher concentrations. In separate experiments, a raised extracellular concentration of magnesium was found to enhance the constrictor response to PGF2 alpha in femoral but not in coronary arteries. Cerebral arteries showed a pattern of reaction that was somewhat different from that observed in peripheral arteries. The level of maximum relaxation by magnesium in cerebral arteries was twice that found in peripheral arteries. Cerebral arteries were significantly more sensitive to verapamil than peripheral arteries.