On the Competition between Metabolic Vasodilatation and Neurogenic Vasoconstriction in Skeletal Muscle1

Abstract

Using a plethysmographic method combined with recording of blood flow and, at times, recording of the volume of blood in the calf of the cat with an isotope technique, the responses of the resistance vessels, of the capillary filtration coefficient and of the capacitance vessels were studied when the vessels were subjected to the antagonistic influences of muscular exercise and vasoconstrictor fibre activity.At the higher frequencies of stimulation used sympathetic activation caused an equally marked reduction of blood flow during exercise as during rest, but during exercise the response of the resistance vessels subsided within a few minutes to become steady at a level only a little above starting level despite continued stimulation. The capillary filtration coefficient, already increased during exercise, was affected, and then increased still further only when the sympathetic were stimulated at such frequencies as impeded blood flow markedly. Sympathetic stimulation during exercise increased the tone of the capacitance vessels—a response that did not weaken at all so soon as that of the resistance vessels.It is concluded that the resistance vessels and particularly the precapillary sphincters are more sensitive to vasodilator metabolites locally released during exercise than to the vasoconstrictor fibre supply, while the reverse is true for the capacitance vessels.