Myogenic mechanisms in the skeletal muscle circulation.

Experiments were carried out on cat skeletal muscle to investigate the myogenic control in local vascular regulation, using a technique which allowed registration of pure myogenic responses to transmural pressure changes. The amplitudes of the responses to standardized transmural pressure increases were used to test myogenic reactivity in various situations. The technique also permitted continuous recordings of vascular resistance in the whole vascular bed and in its three consecutive vascular segments, i.e. proximal arterial vessels (greater than 25 microns inner diameter), microvessels (less than 25 microns) and veins. The experiments confirmed the presence of a myogenic control system triggered by the transmural pressure distension and mainly located in the arterial microvessels. The myogenic control seems to contribute to the initiation and establishment of basal vascular tone and, in synergism with metabolic vasodilator influences, to autoregulation of blood flow. Consequently, factors that depress myogenic reactivity should induce vasodilation, as also shown in the present study for metabolic influence, beta-adrenergic activation and calcium antagonism. Both the humoral and the neurogenic beta-adrenergic effects depress myogenic reactivity and counter alpha-adrenergic constriction.