HIGH-CALCIUM DIET EFFECTIVELY OPPOSES THE DEVELOPMENT OF DEOXYCORTICOSTERONE-SALT HYPERTENSION IN RATS

The effects of increased dietary calcium intake on blood pressure and arterial function were investigate gated in one-kidney deoxycorticoste rone-salt hypertensive Wistar rats. The calcium content of the control diet was 1.1%, and that of the high calcium diet, 2.5%. During the 10 -week study calcium supplementation markedly attenuated the steroid-sa lt-induced rise in blood pressure and the associated cardiac hypertrop hy. Responses of mesenteric arterial rings in vitro were examined at t he end of the study. In deoxycorticosterone-salt-treat ed rats, the co ntractile sensitivity of endothelium-denuded preparations to norepinep hrine, 5-hydroxytryptamine, and KCl, and the inhibitory effect of nife dipine on KCl-evoked responses were enhanced. It is interesting that t he high calcium diet alleviated the steroid-salt-induced increase in s ensitivity to KCl but did not significantly affect it to the receptor- mediated agonists norepinephrine and 5-hydroxytryptamine. Thus, sensit ivity to membrane depolarization was reduced by calcium supplementatio n. Smooth muscle responses were also studied by challenging the prepar ations with KCl in a calcium-free solution, after which calcium was ad ded to the organ bath in increasing concentrations. In steroid-salt-tr eated rats, these calcium contractions were attenuated, but concomitan t calcium supplementation normalized the responses, suggesting improve d cell membrane handling of calcium. In addition, the mineralocorticoi d-salt treatment impaired relaxation responses of endothelium-intact a rterial rings to acetylcholine, sodium nitroprusside, and isoprotereno l. The relaxation to isoproterenol was not appreciably affected by the high calcium diet, whereas the responses to acetylcholine and sodium nitroprusside were clearly improved, indicating augmented sensitivity to endogenous and exogenous nitric oxide. In conclusion, the marked bl ood pressure-lowering action of a high calcium diet in mineralocortico id-salt hypertension may be mediated by its beneficial effects on arte rial smooth muscle function.