Abnormal membrane cation transport in pregnancy-induced hypertension

An abnormality of sodium handling has been suggested as one of the mechanisms responsible for the development of pregnancy-induced hypertension. We analysed the plasma and urinary concentrations, and the intraerythrocyte activities of Na and K, and the RBC membrane Na+/K+-ATPase activity of 77 hypertensive and 133 normal pregnant women. Umbilical cord blood of infants from 21 hypertensive and 28 control women was studied. The Na+/K+-ATPase activity was determined by measuring the inorganic phosphate released by incubation in a reaction medium in the presence and absence of K ions or ouabain. The intra-erythrocyte sodium and potassium activities were measured by ion-selective electrode analysis of the haemolysates, after washing the RBCs in 110 mmol/l MgCl2. We found a significant increase in intracellular sodium and a reduction in Na+/K+-ATPase activity in the hypertensive women in comparison with the control subjects during pregnancy. No difference was observed in early puerperium. Cord blood from infants of pregnancy-induced hypertensive women showed an increase in intracellular Na+ activity and a decrease in the erythrocyte membrane Na+/K+-ATPase activity in comparison with cord blood samples from control subjects. The observed abnormalities in the plasma membrane sodium transport may play a major role in the pathophysiology of pregnancy-induced hypertension.