Effect of Increased Calcium Intake During the Third Trimester on the Vascular Sensitivity to Angiotensin II

Abstract

Calcium supplementation during pregnancy reduces the vascular sensitivity to infused angiotensin II, but the dose of calcium required increases as pregnancy advances. In 24 patients given 600 mg/day of calcium L-aspartate from the 20th week of gestation, the effective pressor doses of angiotensin II at the 20th, 26th, 30th and 36th week of gestation were 18.4±1.1, 31.9±2.3, 39.0±3.0 and 25.7±2.4 ng/kg/min (mean±SEM), respectively. In this group, the decline in the effective pressor dose from the 30th to the 36th week of gestation was significant (p< 0.005). In 21 patients calcium L-aspartate was given at a dose of 600 mg/day from the 20th week and the dose was increased to 1200 mg/day after the 30th week, and the the effective pressor doses were 21.2±2.6, 31.8±3.2, 32.1±3.4 and 28.7±2.6 ng/kg/min at the 20th, 26th, 30th and 36th week of gestation, respectively. In this group, a significant decrease in the effective pressor dose between the 30th and the 36th week of gestation was not observed. In both groups, the effective pressor doses after the 26th week of gestation were significantly larger than those of the 20 control, non-supplemented pregnant women. The baseline blood pressure and the concentrations of serum electrolytes and albumin showed no significant differences between the three groups. Calcium supplementation at twice the dosage during the third trimester of pregnancy is suggested to have a much more favorable effect on angiotensin sensitivity and may have beneficial effect on preventing pregnancy-induced hypertension.