DIETARY CALCIUM AND MAGNESIUM SUPPLEMENTS IN SPONTANEOUSLY HYPERTENSIVE RATS AND ISOLATED ARTERIAL REACTIVITY

1 High calcium diet attenuates the development of hypertension but an associated undesirable effect is that Mg2+ loss to the urine is enhanc ed. Therefore, we studied the effects of high calcium diet alone and i n combination with increased magnesium intake on blood pressure and ar terial function. 2 Forty-eight young spontaneously hypertensive rats ( SHR) were allocated into four groups, the dietary contents of Ca2+ and Mg2+ being: 1.1%, 0.2% (SHR); 2.5%, 0.2% (Ca-SHR); 2.5%, 0.8% (CaMg-S HR); and 1.1%, 0.8% (Mg-SHR), respectively. Development of hypertensio n was followed for 13 weeks, whereafter electrolyte balance, lymphocyt e intracellular free calcium ([Ca2+](i)), and mesenteric arterial resp onses in vitro were examined. Forty normotensive Wistar-Kyoto (WKY) ra ts were investigated in a similar manner. 3 Calcium supplementation co mparably attenuated the development of Lypertension during normal and high magnesium intake in SHR, with an associated reduced lymphocyte [C a2+](i) and increased Mg2+ loss to the urine. 4 Endothelium-dependent arterial relaxation to acetylcholine was augmented in Ca-SHR and CaMg- SHR, while the relaxations to isoprenaline and the nitric oxide donor SIN-1 were similar in all SHR groups. Relaxation responses induced by the return of K+ to the organ bath upon precontractions in K+-free sol ution were used to evaluate the function of arterial Na+, K+-ATPase. T he rate of potassium relaxation was similar in Ca-SHR and CaMg-SHR and faster than in untreated SHR. 5 Contractile responses to high concent rations of potassium and noradrenaline, and the ability of vascular sm ooth muscle to sequester Ca2+, which was evaluated by eliciting respon ses to caffeine or noradrenaline after loading periods in different Ca 2+ concentrations, were comparable in all SHR groups. In SHR with incr eased magnesium intake, and in WKY rats with calcium or magnesium supp lementation, no detectable effects on blood pressure and arterial func tion were observed. 6 In conclusion, high calcium diet attenuated the development of hypertension in SHR, with an associated augmented endot helium-dependent relaxation, promoted recovery rate of ionic gradients across the cell membrane via Na+, K+-ATPase, and reduced basal [Ca2+] (i). Dietary magnesium supplementation, whether combined with normal o r high calcium intake, had no beneficial effects on blood pressure or arterial function.