EFFECTS OF DIETARY CALCIUM RESTRICTION ON VASCULAR CONSTRICTION AND RELAXATION OF THE RAT ISOLATED AORTA

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-depe ndent and endothelium-independent relaxation responses in isolated aor tic rings of the Wistar rat. Compared with the control rat fed a norma l diet (1.04% calcium), the femur mineral density was significantly re duced 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 C -max (the maximum constriction induced by phenylephrine) in aortic rin gs without endothelium, LC3M, but not LC1M, significantly increased CD 50 (the dose of phenylephrine inducing 50% of C-max). On the other han d, the low-calcium diet did not change C-max and CD50 in rings with in tact endothelium. Thel low-calcium diet showed no significant change i n the vasorelaxation responses to acetylcholine (Ach) or sodium nitrop russide (SNP). Cyclic GMP production stimulated by Ach or SNP was not affected by calcium restriction. These results suggest that an insuffi cient calcium supply for three months, attenuates alpha-adrenoceptor-m ediated vasoconstriction in the normotensive rat but vasorelaxation re sponses to Ach or SNP are not affected.