Loci of Neurogenic and Metabolic Effects on Precapillary Vessels of Skeletal Muscle

Abstract F olkow , B., R. R. S onnenschein , and D. L. W right , Loci of neurogenic and metabolic effects on precapillary vessels of skeletal muscle . Acta physiol. scand. 1971. 81 . 459–471. By cannulation of a branch of the proximally clamped sural artery of the anesthetized cat, distal arterial pressure (DAP) in the gastrocnemius muscle was recorded. Measurement of blood flow, femoral arterial pressure and DAP allowed calculation of total resistance (R t ) and its partition into a distal component (R d ) which included precapillary sphincters and the smaller arterioles, and a proximal component (R P ) which included the larger arteries. With sympathetic vasoconstriction, the initial increase in R t was accounted for mainly by constriction of the distal vessels which then tended to relax; progressive constriction of proximal vessels accounted for most of the elevated R t during the steady state; subsequent reactive hyperemia mainly involved distal vessels. R t was less affected by sympathetic stimulation during exercise than when the muscle was at rest; constriction of distal vessels was more markedly reduced than that of proximal vessels. Ascending dilatation was evident during exercise. Sympathetic cholinergic vasodilatation mainly involved vessels more proximal to those which were dilated early in exercise. The findings are compatible with the concept that capillary flow distribution, as a function of terminal arterioles and precapillary sphincters, is adjusted by local factors towards an optimum for the prevailing metabolic level of the tissue.