Comparative Effects of Acetylcholine, Butyl-nor-Synephrine (Vasculat), Noradrenaline, and Ethyl-Adrianol (Effontil) on Resistance, Capacitance, and Precapillary Sphincter Vessels and Capillary Filtration in Cat Skeletal Muscle

Abstract

A comparative analysis was performed of the response patterns within the consecutive sections of a skeletal muscle vascular bed to acetylcholine (Ach), butylnor-synephrine (BNS), noreplnephrine (NA), and ethyl-adrianol (EA). Ach [acetylcholine] and BNS are dilators acting directly on the vascular smooth muscle but evoked different response patterns. Ach dilates all vascular sections, i.e. pre- and postcaplllary resistance vessels, precapillary sphincters and capacitance vessels, while the dilator effect of BNS is mainly confined to precapillary vessels. Both compounds produce net transcapillary filtration, but BNS at a higher rate. NA and EA are constrictors (by [alpha] -receptro engagement) when acting locally on the vascular smooth muscle. They both produce similar patterns of response, i.e. constriction of resistance and capacitance vessels and net transcapillary fluid absorption. They dilate precapillary sphincters, probably due to secondary action of vasodilator metabolites accumulating as regional blood flow decreases. On intravenous administration into the systemic circulation EA evokes an indirect vasodllatatlon in skeletal muscle mediated via the adrenergic sympathetic fibers. Evidence Is presented that at least part of this dilatation is dependent upon engagement of cardiovascular baro-receptors inhibiting the prevailing sympathetic constrictor fibre discharge. The hemodynamic significance of the response patterns of the various vasoactive agents is discussed.