The carotid sinus baroreceptor reflex in conscious rabbits.

Abstract

A method for altering the pressure across the wall of the carotid sinus in conscious rabbits by enclosing the carotid bifurcation in a rigid, fluid-filled capsule is described. The extracapsular arterial baroreceptors were denervated. The baroreceptor-heart rate reflex, elicited by injecting vasoactive drugs or inflating aortic and vena caval cuffs, was used to test the new method. The function of the carotid sinus was unaffected by enclosure in the capsule. Denervation of the extracapsular baroreceptors reduced the gain of the baroreceptor-heart rate reflex 2 to 3-fold. The characteristics of the carotid baroreceptor reflex were studied in 16 animals by the capsule method. Median estimates of maximum gain and the range over which blood pressure changed were 1.1 mm Hg/mm Hg and 57 mm Hg, respectively. Good agreement existed between duplicate estimates made 1-20 days apart. Only a weak association existed between the effects on blood pressure and heart rate of altering carotid sinus transmural pressure. Autonomic blockade of the heart to fix its rate did not reduce the gain or range of blood pressure change.