Calcium and platelets in normotensive and hypertensive human pregnancy

The primary objective of this study was to determine the baseline platelet intracellular free Ca2+ concentration in normotensive and hypertensive primigravid women and to note any correlation between variables (ie. platelet intracellular free Ca2+ concentration and arterial blood pressure).

A cross-sectional study of 24 normotensive and 36 primiparous women whose pregnancies were complicated by gestational hypertension, in the third trimester.

Platelet intracellular free Ca2+, serum Ca2+, and renal clearance of Ca2+ were recorded.

Mean platelet intracellular free Ca2+ concentration was significantly increased in those subjects whose pregnancies were complicated by proteinuric gestational hypertension (pre-eclampsia) compared with the normotensive primiparous control sample. Those subjects with non-proteinuric pregnancy-induced hypertension did not show this significant increase in baseline platelet intracellular free Ca2+ concentration despite having a persistent and statistically significantly elevated systemic arterial blood pressure. On pooling these data for both normotensive and hypertensive primigravidae a significant positive correlation was noted between the variables of platelet intracellular free Ca2+ concentration and arterial blood pressure. The renal clearance of free Ca2+ was progressively reduced with increasing severity of the disease but had returned to normal 6 weeks postpartum. Serum Ca2+ concentrations corrected for albumin were however higher in the hypertensive patients.

Transmembrane Ca2+ fluxes are altered in hypertensive pregnancy by a specific mechanism, probably of placental origin.