Effects of endothelium-derived relaxing factor on the smooth muscle of the rat tail artery.

Simultaneous measurements of smooth muscle membrane potential and tension were made from isolated pieces of rat tail artery. A single electrical stimulus to the perivascular nerves produced a transient contraction of the smooth muscle. The amplitude of the contraction was increased after removal of the endothelium. The excitatory junction potentials and action potentials in the smooth muscle had the same amplitudes before and after removal of the endothelium. Tension obtained by direct stimulation of the arterial muscle in guanethidine-treated arteries was also increased by removal of the endothelium. When the artery was constricted by noradrenaline or 5-hydroxytryptamine, electrical stimulation caused a relaxation that was reduced by removing the endothelium. It was concluded that the electrical stimulus released the endothelium-derived relaxing factor (EDRF) which reduced the amount of contractile force that could be produced by an action potential in the smooth muscle.