Effect of a low calcium intake on the vascular sensitivity to angiotensin II in normotensive pregnant rats.

Abstract

Vascular responsiveness to angiotensin II in pregnant rats with a normal or a low calcium diet were examined. From day 6 of pregnancy, Wistar rats were separated into two groups. One group was fed a normal diet containing 1.2% calcium (control group) and the other group was fed a low calcium diet containing 0.02% calcium (low Ca group). Using a tail cuff method, the systolic blood pressure in the low Ca group was found to be significantly higher than that in the control group on day 18 of pregnancy. On days 12 and 18 of pregnancy using the hindquarters perfusion technique, the vascular response to bolus angiotensin II (30, 100, 300, and 1000 ng/kg of rat body weight) in the low Ca group increased significantly more than that in the control group. However, the pressor response to norepinephrine and the depressor response to acetylcholine did not differ between the low Ca group and the control group. Urinary sodium excretion in the low Ca group was lower than that in the control group on days 12 and 18 of pregnancy, and decreased toward term, whereas urinary phosphorus excretion in the low Ca group was higher than that in the control group on days 12 and 18 of pregnancy. These data indicate that low calcium intake during pregnancy increases sensitivity to the pressor effects of angiotensin II and increases systolic blood pressure in normotensive pregnant rats.