Rabbit carotid baroreflexes after carotid sympathectomy, vagotomy, and beta blockade

Factors that modify carotid vascular baroreflexes were studied in anesthetized rabbits after section of the cervical aortic nerves. We recorded steady-state reflex responses of heart rate (HR) and mean arterial pressure (MAP) to changes in isolated nonpulsatile carotid intrasinus pressures (ISP) over a wide range. These measurements and the procedures were repeated 1) after sympathetic denervation of the carotid sinuses by section of the cervical sympathetic nerve below the superior cervical ganglia; 2) after cervical vagotomy; and 3) after beta-receptor blockade by propranolol administration. The linearity of the MAP-ISP relation curve slope was determined between ISP levels of 63 and 100 mmHg. Comparison of results before and after sympathetic denervation of the sinuses indicated that the denervation significantly lowered the position of the MAP-ISP relation curve over a mid-ISP range. Subsequent vagotomy significantly elevated both HR-ISP relation curve and MAP-ISP relation curve. AFter beta-receptor blockade HR remained constant, whereas the slope of the MAP-ISP relation curve decreased to -1.34 from the slope of -2.26 before blockade. Comparison of results before and after beta blockade in the vagotomized animals suggested a substantial cardiac influence on carotid reflex control of MAP.