Relaxant effects of mefloquine on vascular smooth muscle in vitro.

We have studied the effects of mefloquine on isolated rat aorta. Mefloquine (10(-8) to 1.6 x 10(-4) mol.l-1) relaxed aortic rings precontracted with both noradrenaline (10(-7) mol.l-1) and potassium chloride (60 mmol.l-1). The mefloquine-induced relaxation was somewhat attenuated by removal of the endothelium. Contractile responses to noradrenaline, potassium chloride, and calcium chloride were reduced by incubating the aortic rings in physiological salt solution containing mefloquine, suggesting that mefloquine reduces calcium influx, which is required for excitation-contraction coupling. The results show that mefloquine relaxes vascular smooth muscle via mechanisms which are partly endothelium-dependent and which is also associated with inhibition of Ca2+ influx from the extracellular medium.