Enhanced contractile response to noradrenaline and calcium influx in thoracic aorta isolated from dietary magnesium deficient rats.

Dependency on extracellular calcium influx in contractile response to noradrenaline has been investigated in the thoracic aorta isolated from dietary magnesium (Mg) deficient rats. Adult male Wistar rats were fed with a Mg deficient diet (0.001% Mg) for 30 days, together with control groups (0.07% Mg). The contractile response to noradrenaline in the thoracic aortas from Mg deficient rats was significantly greater than that in the controls. However, there were no significant differences between control and Mg deficient rats in the contractile response to high potassium. The rate of 45Ca uptake induced by noradrenaline was greater in Mg deficient rat aortas than in the controls, but that induced by high potassium showed no significant differences between control and Mg deficient rats. Calcium entry blockers (verapamil and nifedipine) caused a concentration-dependent depression of the noradrenaline-induced contraction. The aortas from Mg deficient rats were more sensitive to these drugs than were those from the controls. These results suggest that the noradrenaline-induced contraction depends much more on extracellular calcium influx in Mg deficient rats than in the controls.