Relation Between Calcium and Cardiovascular Reactivity in Mineralocorticoid‐induced Hypertension in the Rat

Abstract

1 Previous work has shown that parathyroidectomy (PTX) decreases cardiovascular reactivity to noradrenaline in Sprague-Dawley rats with mineralocorticoid-induced (D) hypertension. 2 In order to explain this diminution of cardiovascular reactivity, we studied in vivo the influence of serum calcium levels on the cardiac and vascular response to noradrenaline (500 ng/kg). We used rats with or without parathyroids but fed a standard or a high-calcium (+Ca) diet that re-established a serum calcium level of about 100 mg/l. Work was performed in vagotomized, anaesthetized rats after ganglionic blockade with pentolinium and atropine sulphate. 3 Cardiac output was unchanged in all the experimental groups after 11 weeks of mineralocorticoid treatment. The enhancing effect of noradrenaline was not modified. 4 Since a serum calcium level of about 100 mg/l was sufficient to re-establish vascular reactivity to exogenous noradrenaline in the PTX-D rats, parathyroid hormone was not necessary. 5 The total and lanthanum-resistant calcium fractions of the walls of the aorta were reduced in the PTX-D rats. When serum calcium levels were re-established at about 100 mg/l, there was no difference between PTX-D and D rats. 6 It is postulated that the decreased storage of calcium in vascular smooth muscle cells of PTX-D rats depresses the vascular effect of noradren4line.

Endothelium‐derived Relaxing Factor, Hypertension and Chronic Parathyroidectomy in Spontaneously Hypertensive and Wistar‐kyoto Rats

“…Nevertheless these results were reproducible and obtained with several strains in different experiments. Some of us previous described a decreased pressor to NE in Deoxycorticosterone acetate (D0CA)-treated PTX (Berthelot & Gairard 1978), SHR PTX (Schleiffer et al 1986) and LH PTX (Pernot et al 1990) but when serum calcium was re-established to normal values by a high calcium diet, response to NE returned to normal values (Berthelot et al 1980). Nevertheless blood pressure was still decreased in these DOCA PTX rats.…”