Evidence for a Metabolic Mechanism in Autoregulation of Blood Flow in Skeletal Muscle

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Abstract
Simple criteria have been used in an isolated, perfused skeletal muscle preparation to determine whether autoregulation of blood flow in this tissue is the consequence of a metabolic or a myogenic mechanism. Elevation of venous pressure significantly decreased equilibrium vascular resistance and reduction of venous pressure significantly increased vascular resistance during controlled pressure perfusion whereas alteration of ambient pressure had no significant effect on equilibrium resistance. These responses repudiate a myogenic mechanism for autoregulation of equilibrium blood flow since the myogenic hypothesis predicts increased resistance following increased transluminal pressure and decreased resistance following decreased transluminal pressure. Moreover, during perfusion at constant blood flow, metabolic regulation should be constant and myogenic responses would be permitted full expression. Alteration of venous pressure or ambient pressure during constant flow perfusion, however, failed to evoke myogenic responses at equilibrium. Rather, a passive distention was observed at equilibrium after increased transmural pressure, and passive recoil of the vessels followed decreased transmural pressure during constant flow perfusion. All pressure alterations were accompanied by transient resistance changes of undetermined origin. With the criteria employed, however, the results indicate that the regulation of equilibrium vascular resistance in skeletal muscle is based primarily on a metabolic mechanism.