The Effect of Pregnancy and Pregnancy-Induced Hypertension on Active Sodium Transport in the Erythrocyte

Abstract

Abstract 1. (1) Active sodium transport was assessed in the erythrocytes of pregnant women with and without pregnancy-induced hypertension and in non-pregnant women. 2. (2) The measurements made were the sodium content of washed erythrocytes (Naw), the ouabain-sensitive efflux rate constant (Kos), the ouabain-sensitive sodium flux (Mos) and the number of sodium pumps (as the ouabain-binding capacity; OB). 3. (3) The sodium content was reduced in the pregnant women due to an increase in the efflux rate constant and this increase was due to an increased number of sodium pumps (by 50%) which swamped a 20% reduction in the rate constant per pump. 4. (4) There was a general reduction in the permeability of the erythrocyte to sodium but at the same time there was an increase in permeability in association with the increased number of sodium pumps. The greater variability of permeability and therefore of sodium flux in the pregnant women was explained by the variable increase in the number of sodium pumps. 5. (5) There were no significant differences in these measurements between the hypertensive and the normotensive pregnant women and in particular there was no difference in the degree of pump inhibition. 6. (6) These results suggest that the major change in active sodium transport in pregnancy is an increase in the number of sodium pumps. We suggest that this is a part of the wide ranging effect of pregnancy on protein synthesis and not a specific effect on sodium transport. There is an inhibition of the sodium pump in pregnancy but it does not cause an increase in the sodium content of the erythrocytes because there is also an increase in the number of sodium pumps. The inhibition is no greater in hypertensive than in normotensive pregnancies.