Rise of blood pressure in calcium-deprived pregnant rats JOSE M. BELIZAN, M.D., PH.D. OSCAR PINEDA, PH.D. EDUARDO SAINZ, M.Sc. L. ANNABELLA MENENDEZ, B.S. JOSE VILLAR, M.D., M.P.H., M.Sc.* Guatemala, Guatemala, Central America It has been postulated that calcium intake is inversely related to blood pressure (BP) in animals and pregnant women. To test this hypothesis, 34 female, 142-day7old Wistar rats were studied prospectively. They were randomly assigned to either a cal_cium-free diet (16 rats) or a normal diet (18 rats). Weekly measurements of tail systolic BP showed a statistically significant increase in BP in the calcium-free group after 6 weeks of treatment. After 9 weeks on this diet, the animals were mated. Five in the control group and six in the calcium-free group became pregnant. Thereafter, both of these subgroups (pregnant and nonpregnant calcium-free diet) continued with significantly higher BP until they were put to death. Blood samples taken at the end of the study showed significantly lower values of calcium/magnesium (Ca/Mg) ratio, but higher inorganic pl)osphate in the group consuming a calcium-free diet. Blood pressure during the last 3 weeks of the study was significantly inversely correlated with the blood Ca/Mg ratio and directly correlated with magnesium and inorganic phosphate values. This article supports the hypothesis that a low-calcium diet is associated with high BP in pregnant and nonpregnant female rats. (AM. J. OBSiEi. GYNECOL 141:16a, 1981.) RECENTLY, we have postulated a possible association between calcium intake and pregnancy-induced hyper- tension (PIH) in the sense that low calcium intake could favor the appearance of the disease. 1 Our hypothesis is based on the following observations: (l) Populations with a high calcium intake have a low incidence of PIH. This relationship does not depend on the better nutri- tional and socioeconomic conditions of these popula- From tht Division of Biolol!'l and Human Nutrition, Institute of NutritU:n of America and Panama. Supporttd by the Pan American Health Organi:wtion (Grant No. 79-WTP-AMR-I300) and the United Nations Fund for Population Activities. INCAP Publication I-1164. Received for publication December 29, 1980. Revised March 9, 1981. Accepted April 3, I 981. Reprint requests: Dr. Jose M. Beliziln, pepartamento de Obstetricia, Hospital Italiano, Entre Rios 2850, 2000 Rosario, Argentina. *Present address: Department of Maternal and Child Health, The fohns Hopkins University School of Hygiene and Pubiic Health, Baltimore, Maryklnd. 0002-9378/81/l80t63+07$00.70/0© 1981 The C. V. Mosby Co. tions. Some very poor populations consuming high- calcium diets show low incidences of PIH. Such is the case in Guatemala, where the staple food is lime-treated corn (tortilla), and in Ethiopia, where the staple food is teff, a calcium-rich cereal grain. (2) The results from several studies of supplementation during pregnancy, in which calcium was utilized along with other nutri- ents, show a significant decrease in the incidence of PIH. (3) The possible relative calcium deficit during pregnancy is due to the high requirements for fetal development and the decrease in renal and osseous compensating mechanisms for hypocalcemia. In a previous publication/ we argued that populations with low calcium intake could have higher blood pressure rates, which would favor the appearance of PIH. Human epidemiologic studies are available which as- sociate calcium intake with blood pressure. The study of populations which consume "hard water" (high cal- cium content) revealed lower incidences of stroke be- cause of lower blood pressure rates. 2 • 3 In a study car- ried out in New Guinea, it was shown that as the water from an isoiated river flowed away from its source, its 163