Length at Inactivated Contractile Elements, Length‐tension Diagram Active State and Tone of Vascular Smooth Muscle

Abstract Analysis of the mechanical properties of vascular muscle is complicated by the fact that normally it is contracted to a certain degree and has no constant resting length. By total blockade of the energy production of the muscle with monoiodoacetic acid under anaerobic conditions the vessel length at inactivated contractile elements could be measured. With the aid of this length the length‐tension diagram of the vascular muscle in untreated and adrenaline‐treated vessels was studied. The muscle developed a maximal tension (2.100gwt/cm 2 cross section) at this length, which therefore probably corresponded to L 0 in skeletal muscle. The vascular muscle shortened maximally to 25 per cent of the relaxed length. Both the development of maximal isometric tension and the maximal isotonic shortening were of the same magnitude in vascular as in skeletal muscle. The series‐elastic component (15–20 per cent) was, on the other hand, greater in vascular than in skeletal muscle. No rigor mortis was noted in the vascular muscle. The spontaneous tension of the vascular muscle and tension increase induced by adrenaline could be largely ascribed to an active state. The question of whether a “tonic” or “catch” mechanism is present in vascular muscle, independent of the active state, is discussed.