INTRAPLATELET FREE CALCIUM AND CALCIUM-REGULATING HORMONES IN PLASMA ARE NOT RELATED TO THE ANTIHYPERTENSIVE EFFECT OF NIFEDIPINE IN HYPERTENSIVE PREGNANCY

Intracellular free calcium regulates contraction-relaxation processes in vascular smooth muscle. We compared intraplatelet free calcium ([Ca 2+](i)) and pH ([pH](i)) in hypertensive pregnant women to those in no rmotensive pregnant and non-pregnant women. Plasma parathormone and vi tamin D metabolite were simultaneously assessed. In hypertensive pregn ancy [Ca2+](i) tended to be lower than in normotensive pregnant (P = 0 .08) and non-pregnant subjects (P = 0.06). In hypertensive pregnancy, 1,25 (OH)(2) vitamin D in plasma was in the same range as in non-pregn ant women and significantly lower than in normotensive pregnancy (p < 0.01). The other two vitamin D metabolites, parathormone and [pH](i) w ere equal in the three groups. A five-day nifedipine treatment (10 mg t.i.d.) increased [Ca2+](i) in hypertensive pregnant (P < 0.05) and no rmotensive non-pregnant subjects (P = 0.06), whereas [pH](i) (P < 0.05 ) and 25 (OH) vitamin D (P < 0.05) decreased in the former and 24,25 ( OH)(2) vitamin D increased in the latter group (P < 0.05). Initial [Ca 2+](i) did not correlate with blood pressure in any group. The antihyp ertensive effect of nifedipine did not correlate with any variable mea sured. In conclusion, [Ca2+](i) and calcium-relating hormones seem not to be related to the antihypertensive effect of nifedipine in hyperte nsive pregnancy. In this type of hypertension, intraplatelet calcium m ay not reflect calcium balance in smooth muscle cells regulating vascu lar tone and blood pressure.