Pathophysiology of Aortic Baroreceptors in Rabbits with Vitamin D Sclerosis and Hypertension

Abstract

Calciferol (vitamin D₂) (50,000-100,000 IU) and calcium lactate (1 g) were added to the normal diet of 22 rabbits for 7-11 days. When mean arterial blood pressure had risen from a control value of 87.2 ± 3.7 mm Hg to an experimental value of 137.8 ± 5.7 mm Hg (11-145 weeks), the aortic arch of 9 of these rabbits was isolated and perfused with Krebs-Henseleit solution. The impulse activity in 75 aortic baroreceptor fibers from the left aortic nerve was studied during nonpulsatile perfusion at different pressures and was compared with the impulse activity in 29 fibers from 17 normal rabbits. The threshold pressures and the pressure at the point of inflection of the curves were lower in these fibers than they were with fibers from normal rabbits. The gradient of the curves relating baroreceptor impulse frequency to aortic pressure was depressed from a normal mean value of 1.19 impulses/sec mm Hg^-1 to 0.61 impulses/sec mm Hg^-1 (P < 0.001). A similar depression of the gradient was found in 7 baroreceptor fibers from the right aortic nerve. The change in the sensitivity of the baroreceptors was more closely related to the time interval after the calciferol treatment (r=-0.95) than it was to the mean arterial blood pressure (r= -0.76). The pressure-volume curves show that it was also related to the decreased distensibility of the aortic arch region. Histologically, the aortic arch region had extensive medial sclerosis with calcification.