Characteristics of Single Aortic and Right Subclavian Baroreceptor Fiber Activity in Rabbits with Chronic Renal Hypertension

Abstract

Experimental renal hypertension was induced in rabbits by wrapping polyethylene around one kidney and removing the other. The impulse activity in single baroreceptor fibers of the aortic nerves to the aortic arch and the right subclavian areas was studied 7-19 weeks postoperatively during nonpulsatile perfusion of an isolated aortic arch preparation. The results were compared with those obtained in normal rabbits. Curves relating the impulse frequency to the aortic arch pressure were constructed. In rabbits with hypertension, the threshold pressure of the aortic baroreceptor fibers was increased from a normal value of 52.5 ± 5.5 to 106.5 ± 5.8 mm Hg, and the point of inflection was increased from 112.4 ± 6.2 to 163.4 ± 5.1 mm Hg. The sensitivity of the baroreceptors to changes in pressure was reduced from 1.19 ± 0.14 to 0.64 ± 0.06 impulses/sec mm Hg^-1. Similar results were obtained for the right subclavian area. Hysteresis, as indicated by the separation of the curves produced by first increasing and then reducing the aortic pressure, was more evident in rabbits with hypertension than in normal rabbits. The changes in baroreceptor activity in rabbits with hypertension were associated with alterations in the mechanical properties of the arterial walls, which were demonstrated by the pressure-volume curves. Also, there were demonstrable histological lesions of the arterial walls and the receptors in rabbits with hypertension.