CALCIUM-METABOLISM, PLASMA PARATHYROID-HORMONE, AND CALCITRIOL IN TRANSIENT HYPERTENSION OF PREGNANCY

In order to know if abnormalities of calcium metabolism may be involve d in the pathophysiology of pregnancy-induced hypertension (PIH), as i t has been incriminated in essential hypertension, we measured plasma and urinary calcium and phosphate as well as plasma PTH and free calci triol index (ratio of total calcitriol on the D binding protein) in no rmotensive pregnant women (n = 25), in women with PIH after the same d uration of amenorrhea (> 28 wk, n = 21: preeclampsia and 20 transient hypertensions), and in age-matched nonpregnant women (n = 15). The sev erity of PIH was mild since blood uric acid was not increased and plas ma volume, measured with the Evans blue technique, was found only mode rately decreased (-10.5 +/- 3.1% of normal value). The results show th at normotensive pregnant women showed the expected increase of the vit amin D parameters in comparison to nonpregnant controls. Hypertensive pregnant women were not different from the normotensive ones regarding plasma corrected calcium and phosphate and urinary excretion of calci um and phosphate, but had higher plasma PTH (13 +/- 1 v 8.8 +/- 1.6 pg /mL) and lower total and free calcitriol index (86 +/- 7 v 110 +/- 6 p g/mL and 1.72 +/- 0.10 v 2.25 +/- 0.13 X 10(-5)). Correlative studies showed PIH having a negative correlation between blood pressure and pl asma corrected calcium (r = -0.43, P < .05), which is in agreement wit h epidemiological studies of essential hypertension. In conclusion, di sturbances of calcium regulating hormones do exist in transient forms of pregnancy-induced hypertension. In contrast to their increase in es sential hypertension, plasma calcitriol levels are not so high in tran sient hypertension of pregnancy as compared to normotensive pregnancy, as it has been already shown in preeclampsia. All the above data take n together suggest that in both forms of pregnancy-induced hypertensio n, there is a primary defect of calcitriol synthesis in contrast to es sential hypertension.