Effects of anoxia on the vascular resistance of the dog's hind limb.

A NOXIA is known to induce a biphasic effect on blood flow to the extremities. In anesthetized dogs, there is a decrease in blood flow to the leg during anoxia but this is immediately followed by an increase during reoxygenation. 1-3 Since thermoelectric methods have been used for recording blood flow, it has not been possible to express the vascular responses quantitatively to the same extent as the effects of anoxia on cardiac output and pulmonary vascular resistance. 4 There is general agreement that the initial reduction in blood flow to the extremities is due to neurogenic vasoconstriction, 1 " 3 but the role of chemoreceptors in the carotid and aortic bodies lack direct proof. The increase in blood flow to the extremities during reoxy-genation is due to actual vasodilatation, but the mechanism has been claimed to be either nervous 2 or local in nature. 3 ' 5 The experiments that are reported below are attempts to fill these existing gaps in information. The role of nervous mechanisms is explored by surgical denervation and by a new type of sympathetic blocking drug, bretylium bromide. This drug has been shown to block selectively the sympathetic nerves but spare the actions of catecholamines.