Hypocalcemia and Pregnancy-Induced Hypertension Produced by Low-Calcium Diet

• Published in: Hypertension (Dallas, Tex. 1979) Tex. 1979), 1994-06, Vol.23 (6, Part 1), p.695-702
• Main Authors: Prada, Jorge A, Tsang, Reginald C, Clark, Kenneth E
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calcium, Dietary - administration & dosage; Cardiovascular System - physiopathology; Diseases of mother, fetus and pregnancy; Female; Fetus - physiology; Gases - blood; Gynecology. Andrology. Obstetrics; Hypertension - etiology; Hypertension - pathology; Hypertension - physiopathology; Hypocalcemia - etiology; Kidney - pathology; Medical sciences; Pregnancy; Pregnancy Complications, Cardiovascular - etiology; Pregnancy Complications, Cardiovascular - pathology; Pregnancy Complications, Cardiovascular - physiopathology; Pregnancy, Multiple; Pregnancy. Fetus. Placenta; Sheep; Twins
• ISSN: 0194-911X; 1524-4563
• DOI: 10.1161/01.hyp.23.6.695

Recent studies from our laboratory in fasting pregnant ewes with twin gestation have implicated low serum calcium concentration in the etiology of hypertension in pregnancy. We hypothesized that the reduction in serum calcium concentration produced by feeding of a calcium-deficient diet in twin gestation would lead to a significant increase in maternal 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 blood flow were monitored every other day. Six control animals were provided with standard Rumilab diet and tap water (group 1). Animals on a lowcalcium diet (group 2) were subdivided according to the blood ionized calcium response to low dietary calcium intake. Nonhypocalcemic animals were assigned to group 2a (n=10), and hypocalcemic animals (calcium concentration below two standard deviations from the control group) were assigned to group 2b (n=9). In group 2b calcium concentration decreased 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 increased from 1.7±0.3 to 10.5±1.2g/L. Despite the fact that all animals in group 2 had the same low dietary calcium intake, group 2a did 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 plays a significant role in regulating systemic arterial blood pressure and uteroplacental blood flow in twin pregnant ewes.