EFFECTS OF CALCIUM AND POTASSIUM SUPPLEMENTS ON ARTERIAL TONE IN-VITRO IN SPONTANEOUSLY HYPERTENSIVE RATS

1 Calcium and potassium intakes inversely correlate with blood pressur e in experimental hypertension. Therefore, we examined the effects of calcium and potassium supplements alone and in combination on arterial tone in spontaneously hypertensive rats (SHR). Wistar-Kyoto (WKY) rat s served as normotensive controls. Calcium and potassium contents in t he control diet were both 1%, while those in supplemented chows were 3 % and 3.5%, respectively. The sodium content of all diets was moderate ly elevated to 1.1%. 2 After 12 weeks of the study systolic blood pres sures in SHR on high calcium and on high potassium diets were markedly lower (about 53 and 58 mmHg, respectively) than in hypertensive contr ols, while combined supplementation of these cations reduced blood pre ssure even further (about 69 mmHg). 3 Responses of mesenteric arterial rings in vitro were examined at the end of the study. Both high calci um and high potassium diets improved the impaired relaxation to acetyl choline (ACh) in SHR, while the combination of these supplements compl etely normalized this response. Cyclo-oxygenase inhibition by diclofen ac augmented the relaxation to ACh in hypertensive controls but not in the other groups. Nevertheless, enhanced endothelium-mediated dilatat ion was still observed in the presence of diclofenac and the nitric ox ide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME) in a ll supplemented groups. Interestingly, additional blockade of Ca2+-act ivated K+ channels by tetraethylammonium abolished the improved relaxa tion to ACh in SHR on high calcium and on high potassium, but distinct responses were still observed in WKY rats and SHR on the combined sup plement. 4 When hyperpolarization of smooth muscle was prevented by pr econtraction of the preparations with 50 mM KCl, only marginal differe nces were observed in the diclofenac and L-NAME-resistant relaxations to ACh between the study groups. Finally, endothelium-independent vaso relaxations of noradrenaline-precontracted rings to nitroprusside, iso prenaline and cromakalim were comparably augmented by all supplements. 5 In conclusion, the vascular mechanisms underlying the antihypertens ive effect of high calcium and high potassium diets during moderately elevated sodium intake in SHR may involve enhanced arterial hyperpolar ization, increased smooth muscle sensitivity to nitric oxide and decre ased production of vasoconstrictor prostanoids. The administration of these cations in combination was more effective than either of them al one in reducing blood pressure and restoring arterial tone.