PREECLAMPSIA IS NOT ASSOCIATED WITH ALTERED PLATELET VASOPRESSIN BINDING AND CYTOSOLIC CA++ CONCENTRATION

OBJECTIVES: Preeclampsia is an important cause of fetal and maternal m orbidity and mortality. Recently it was described that platelet cytoso lic Ca++ levels could be used to screen for preeclampsia. The current study investigated platelet arginine vasopressin receptor characterist ics, platelet cytosolic Ca levels, plasma- and platelet-bound arginine vasopressin in white pregnant women. STUDY DESIGN: In a cross-section al study nine third-trimester nulliparous pregnant women with gestatio nal hypertension (seven with proteinuria, two with excessive weight ga in without proteinuria) were compared with nine healthy nulliparous pr egnant women matched for gestation length and age and 10 healthy age-m atched nonpregnant women. Determined were (1) platelet arginine vasopr essin receptor number and affinity, (2) platelet cytosolic Ca++ levels , both basal and on arginine vasopressin or thrombin stimulation, and (3) plasma- and platelet-bound arginine vasopressin levels. RESULTS: N one of the measured parameters differed significantly among the three groups studied. Mean arginine vasopressin receptor number and affinity ranged from 108 to 143 receptors per platelet and 0.35 to 0.40 nmol/L , respectively. A single population of binding sites was found (Hill n umber 0.96). Basal Ca++ levels ranged from 113.4 to 133.3 nmol/L, on a rginine vasopressin stimulation from 199 to 250 nmol/L. Median arginin e vasopressin levels in platelet-poor plasma were between 1.2 and 2.4 pg/ml, with circulating platelets being estimated to possess two to fi ve molecules of arginine vasopressin per platelet. A significant corre lation was found between platelet cytosolic Ca++ levels before and aft er arginine vasopressin stimulation (r = 0.69, p < 0.001) and a weak c orrelation between platelet receptor density and arginine vasopressin- stimulated platelet cytosolic Ca++ levels (r = 0.38, p < 0.05). CONCLU SIONS: The studied parameters, platelet cytosolic Ca++ levels, whether basal or after stimulation with arginine vasopressin and vasopressin platelet receptor density and affinity, do not discriminate already hy pertensive or preeclamptic white women from nondiseased subjects. A va luable test to screen for preeclampsia awaits further prospective stud ies.