Effects of carotid baroreceptor reflexes on venous tone in skeletal muscle and intestine of the cat.

Abstract

Hadjiminas, J. and B. Öberg. Effects of carotid baroreceptor reflexes on venous tone in skeletal muscle and intestine of the cat. Acta physiol. scand. 1968. 72. 518–532. The engagement of skeletal muscle and intestinal veins in baroreceptor reflexes was quantitatively evaluated by comparing the reflex responses of the resistance and capacitance vessels with those obtained with direct stimulation of the regional vasoconstrictor fibres. Such comparisons revealed that the reflex constriction of skeletal muscle veins, following a diminution of baroreceptor activity, was, in general, considerably smaller than the concomitant resistance vessel constriction. This discrepancy points to a definitely lower, reflex discharge rate in the venoconstrictor fibres. When, however, vasomotor centre excitation, following withdrawal of baroreceptor restraint, was intense, the ensuing venoconstriction in skeletal muscles became as pronounced as that of the resistance vessels. In the intestine, the reflex responses of the capacitance and resistance vessels were always equally pronounced, indicating an essentially uniform reflex discharge rate in all intestinal vasomotor fibres. However, in comparison with the muscle resistance vessels, the intestinal vascular bed seems to be only moderately involved in baroreceptor reflexes. — It is concluded that the capacitance vessels in the studied circuits participate in baroreceptor reflexes but less extensively than the muscle resistance vessels. The functional significance of the differentiated reflex vascular response pattern in skeletal muscles is discussed with special reference to the consequences for the net fluid exchange across the capillaries.