Arterial Baroreceptor Activity in Rabbits with Experimental Atherosclerosis

Abstract

A total of 16 rabbits developed atherosclerosis after receiving a diet containing 1% cholesterol and 6% sunflower seed oil for up to 67 weeks. Their mean blood pressure rose from 85 to 114 mm Hg. The aortic arch region was isolated and perfused with Krebs-Henseleit solution, and the impulse activity of 70 single aortic and 8 right subclavian baroreceptor fibers was studied during step increases and decreases in perfusion pressure. The threshold pressure of the aortic baroreceptor fibers from the atherosclerotic rabbits was only slightly higher (P > 0.4) than that of 29 fibers from 17 normal rabbits, but the impulse frequency was less (P < 0.02). The gradient of the impulse frequency-pressure curves (0.73 impulses/sec mm Hg^-1), was significantly lower (P < 0.01) than normal (1.19 impulses/sec mm Hg^-1), as was the gradient of the curves from the right subclavian baroreceptor region. The curves resulting from first increasing and then decreasing the perfusion pressure were more separated in the atherosclerotic rabbits than they were in the normal rabbits. There was a correlation between the amount of the reduction in the sensitivity of the aortic baroreceptors and the length of time the rabbits had been on the lipemic diet (r = 0.96). The changes in the baroreceptor activity were associated with a reduction in the distensibility of the perfused area and with histological lesions in the baroreceptors and the arterial walls. The mild hypertension in the atherosclerotic rabbits could partly be accounted for by the reduction in aortic baroreceptor activity. Similar mechanisms might contribute to blood pressure anomalies in humans with atherosclerosis.