Magnesium inhibits the responses to neuropeptide Y in the rabbit coronary artery

Neuropeptide Y (NPY) has been shown to cause direct vasoconstriction of coronary arteries in many species, including dogs, rabbits and man, which is selectively inhibited by calcium-channel blocking agents. Recently, NPY has also been reported to inhibit the relaxation to noradrenaline in isolated rabbit coronary arteries, but the composition of the Krebs solution described in this study indicated that it contained no magnesium. Since magnesium is known to be a physiological antagonist of calcium and to have a profound influence on the contraction of coronary vascular smooth muscle, we examined the importance of magnesium in modulating both the direct vasoconstrictor response to NPY and the NPY-induced inhibition of relaxation to noradrenaline, using ring preparations of rabbit circumflex coronary artery.