Influence of Vasoconstrictor Nerve Activity on the Cholinergic Vasodilator Response in Skeletal Muscle in the Dog

Abstract The cholinergic sympathetic vasodilator nerves were activated by topical stimulation in the hypothalamus and the mesencephalon during graded levels of vasoconstrictor nerve activity. Chloralose anestletized as well as conscious dogs were used. In the anesthetized dogs the isolated gracilis muscle was perfused with blood at a constant flow rate. The perfusion pressure was recorded. In unanesthetized dogs blood flow was measured with an electromagnetic flow‐meter probe placed around the external iliac artery. Increase in vasoconstrictor nerve activity was produced either by clamping one or both common carotid arteries or by central topical stimulation through electrodes in the vasoconstrictor areas in the hypothalamus. Activation of cholinergic vasodilator nerves produced a vasodilator response in the skeletal muscles. An increase in vasoconstrictor tone inhibited the effect of threshold vasodilator nerve stimulation. However, when the vasodilator nerves were stimulated with suprathreshold intensity the vasodilator response could be produced even at an elevated vasoconstrictor tone. On the other hand a very pronounced vasoconstrictor tone, only possible to produce in the anesthetized dogs, reduced the vasodilator response in some experiments. The experimental findings indicate a peripheral antagonism between the two types of vasomotor nerves, however, at least in dogs this is presumably of minor physiological importance. A strong activation of cholinergic vasodilator nerves may increase the muscle blood flow even if the arterioles are under increased vasoconstrictor nerve activity.