H. Makynen et al., DIETARY CALCIUM AND MAGNESIUM SUPPLEMENTS IN SPONTANEOUSLY HYPERTENSIVE RATS AND ISOLATED ARTERIAL REACTIVITY, British Journal of Pharmacology, 115(8), 1995, pp. 1455-1462
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.