Optical Anisotropy and Mechanical Behavior of Smooth Muscle of the Longitudinal Layer of Dog Ileum

Abstract

A method was devised and apparatus constructed for the rapid recording of optical phase retardation and tension of living muscle. Studies were made of tension and phase retardation of the longitudinal layer of smooth muscle from the dog ileum during a) slow stretch, b) rapid stretch and subsequent stress relaxation, and c) active contraction induced by acetylcholine. During slow stretch, phase retardation increased without appreciable increase in tension until the muscle length was nearly twice its length in the intestine. At greater lengths, tension increased, while phase retardation decreased with increasing length. When the muscle was stretched rapidly, the tension increased, then decreased as stress relaxation occurred. Phase retardation increased if the final length was equal to or less than that at which retardation peaked in slow stretches, but did not change if the final length was greater than the peaking length. During the stress relaxation which followed, phase retardation always decreased. In active contraction, phase retardation decreased.