Effect of stretch on passive tension and contractility of isolated vascular smooth muscle

Helically cut strips of the wall of small branches of dog superior mesenteric artery were stretched in a stepwise fashion. Tension developed in response to stretch or to a standard stimulus (epinephrine or electricity) was recorded isometrically. The elastic diagram of the vessel is comparable to that reported by other investigators. Contraction in response to a standard stimulus increased with stretch, as much as 100% for a 10% increase in length. The increase in response continued until the strip reached a certain optimal length (variable from strip to strip), after which the response decreased with further stretch. When the strip was released in a stepwise fashion hysteresis was observed. Possible relationships of tension and length at the level of the contractile element are discussed together with ways in which the information presented here may relate to myogenic autoregulation.