PREGNANCY INDUCED HYPERTENSION AND SODIUM-PUMP FUNCTION IN ERYTHROCYTES

Objective To determine if erythrocyte sodium pump function is altered with the onset of pregnancy induced hypertension. Design A prospective descriptive study. Subjects Thirty-two primigravid women with pregnancy-induced hypertension (17 had proteinuria) and 32 gestation-matched normotensive primigravid pregnant women were studied and measurements repeated 20 weeks after delivery. Intervention Erythrocyte sodium, ouabain-sensitive sodium flux and the sodium pump rate constant were measured in whole blood and the maximum velocity and sodium affinity of the sodium pump were measured in vitro. Results Blood pressure remained higher after delivery in the women who had been hypertensive during pregnancy. In normal pregnancy erythrocyte sodium was decreased, and ouabain-sensitive sodium flux, the sodium pump rate constant and maximum velocity (V(max)) were increased compared with 20 weeks after delivery. In pregnancy-induced hypertension erythrocyte sodium and sodium pump changes were the same as in normal pregnancy. The possibility of a positive association between changes in erythrocyte sodium and in blood pressure was excluded. The rate constant of the sodium pump in blood was related to its V(max) measured in vitro but the relation had greater variance in the hypertensives with 7 of the 32 women having rate constants greater than expected from their V(max). Conclusion There was no evidence of sodium pump inhibition or a rise in intracellular sodium associated with increased blood pressure in pregnancy. There may have been stimulation of the sodium pump by a plasma factor in some hypertensive women.