Evaluation of Vasodilator Mechanisms in the Canine Hind Leg; Question of Dorsal Root Participation

Abstract

Vasodilatation was produced in the hind leg of more than 100 anesthetized dogs by stimulation of the peripheral portion of sectioned spinal roots, the carotid or aortic baroceptors, or the medullary vasodepressor center. The vasomotor responses were evaluated by recording the femoral arterial flow rate with a rotameter together with the systemic arterial pressure. The perfusion pressure was always maintained at a stable level and a cross-circulation system was used for this purpose during reflex hypotension. The influence of intact collateral arteries was investigated. Hydergine, an adrenergic blocking compound closely.related to ergotoxine, abolished the constrictor response to ventral root stimulation while large doses of atropine abolished the dilator response to ventral and dorsal root stimulation. These results confirmed the existence of sympathetic adrenergic constrictor, sympathetic cholinergic dilator and dorsal root dilator fibers. The vasodilator response to reflex stimulation was entirely abolished by lumbar chain ganglionectomy or hydergine, but not affected by atropine or surgical elimination of the dorsal root system. It is concluded that the only mechanism for eliciting dilatation through medullary reflexes is inhibition of sympathetic constrictor impulses.