HYPOCALCEMIA AND PREGNANCY-INDUCED HYPERTENSION PRODUCED BY LOW-CALCIUM DIET

Recent studies from our laboratory in fasting pregnant ewes with twin gestation have implicated low serum calcium concentration in the etiol ogy of hypertension in pregnancy. We hypothesized that the reduction i n serum calcium concentration produced by feeding of a calcium-deficie nt diet in twin gestation would lead to a significant increase in mate rnal arterial blood pressure, vascular resistance, and protein in the urine and decreased uterine blood flow. Twenty-five instrumented ewes were used in the present study. After surgery a calcium-deficient diet and deionized water (calcium ion free) were provided ad libitum to 19 animals. Blood pressure, cardiac output, heart rate, and uterine bloo d flow were monitored every other day. Six control animals were provid ed with standard Rumilab diet and tap water (group 1). Animals on a lo w-calcium diet (group 2) were subdivided according to the blood ionize d calcium response to low dietary calcium intake. Non-hypocalcemic ani mals were assigned to group 2a (n=10), and hypocalcemic animals (calci um concentration below two standard deviations from the control group) were assigned to group 2b (n=9). In group 2b calcium concentration de creased from 1.03 +/- 0.04 mmol/L on day 110 of gestation to 0.77 +/- 0.03 mmol/L by day 125 of gestation. Arterial blood pressure increased significantly from 76 +/- 2 to 91 +/- 2 mm Hg, and uterine blood flow decreased from 950 +/- 53 to 579 +/- 48 mL/min. Urinary protein incre ased from 1.7 +/- 0.3 to 10.5 +/- 1.2 g/L. Despite the fact that all a nimals in group 2 had the same low dietary calcium intake, group 2a di d not develop hypocalcemia (by definition) or an increase in arterial blood pressure. The control group (n=6) showed no significant changes in the parameters studied. From these data we suggest that calcium pla ys a significant role in regulating systemic arterial blood pressure a nd uteroplacental blood flow in twin pregnant ewes.