Active relaxation of unstriated muscle produced by adrenaline

Abstract

Adrenaline is one of the most powerful inhibitors of tone in unstriated muscle; it is therefore expected to produce active relaxation. Active relaxation by adrenaline has been found in pieces of circular muscle of frog's stomach and in guinea pig's uterus. The movements of unstriated muscle, compared with those of striated muscle, are very sluggish, so that complicated apparatus is not necessary to follow contraction and relaxation. These experiments with adrenaline and frog's stomach muscle are most satisfactory, as there is no preliminary contraction except that of the normal tone, and the muscle just lengthens.