Effects of dietary calcium restriction on vascular constriction and relaxation of the rat isolated aorta.

ABSTRACT

The blood pressure of the rat is influenced by the dietary restriction of calcium. Since the vasomotor activities may be affected by calcium restriction, we measured vasoconstriction as well as endothelium-dependent and endothelium-independent relaxation responses in isolated aortic rings of the Wistar rat. Compared with the control rat fed a normal diet (1.04% calcium), the femur mineral density was significantly reduced in the rat fed the low-calcium (< 0.01%) diet for one month (LC1M) or for three months (LC3M). Although neither LC1M nor LC3M changed Cmax (the maximum constriction induced by phenylephrine) in aortic rings without endothelium, LC3M, but not LC1M, significantly increased CD50 (the dose of phenylephrine inducing 50% of Cmax). On the other hand, the low-calcium diet did not change Cmax and CD50 in rings with intact endothelium. Thel low-calcium diet showed no significant change in the vasorelaxation responses to acetylcholine (Ach) or sodium nitroprusside (SNP). Cyclic GMP production stimulated by Ach or SNP was not affected by calcium restriction. These results suggest that an insufficient calcium supply for three months, attenuates alpha-adrenoceptor-mediated vasoconstriction in the normotensive rat but vasorelaxation responses to Ach or SNP are not affected.