Platelet sodium/hydrogen ion exchange in normal pregnancy and non-proteinuric pre-eclampsia

In non-pregnant individuals, abnormalities in cation transport in vascular tissues have been linked to essential hypertension. In the present study, we consider whether Na+/H+ exchange (NHE) is affected in non-proteinuric pre-eclampsia (NPP). Platelet NHE characteristics and plasma cholesterol were measured in a cross-sectional study of normal primigravidae at 14 +/- 0.5 (n = 9), 29 +/- 0.7 (n = 7), 39 +/- 0.4 (n = 8) weeks gestation, in women with NPP (n = 15) and in non-pregnant women (n = 8). Amiloride-sensitive 22Na uptake was measured in platelets which had been acid loaded, to stimulate NHE, by suspension in isotonic potassium propionate buffer (pH 6.7). Intraplatelet radioactivity was used to calculate the affinity (Km) and the capacity (Vmax) of Na+ uptake. In normotensive women, Vmax (mean +/- s.e.) at 14, 29, 39 weeks gestation and 6 weeks postpartum were 452 +/- 46, 469 +/- 33, 713 +/- 101 and 562 +/- 77 pmolNa+/10(6) cells/min respectively; the third trimester values were higher (P < 0.05) than those in the first and second trimester and were also higher than those of non-pregnant women (415 +/- 20). Vmax of patients with NPP in the third trimester (712 +/- 44) was not different from gestational age-matched controls. Km values were not affected by gestational age or NPP. Plasma cholesterol concentration was positively correlated with Vmax values during normotensive pregnancy (r = 0.493, P < 0.05). In conclusion, the capacity for amiloride-sensitive Na+ uptake by platelets correlates positively with gestational age during normal pregnancy. However, neither the capacity nor affinity for Na+ was altered in NPP platelets suggesting that NHE is not implicated in the pathophysiology of this condition.