Pregnancy induced hypertension and sodium pump function in erythrocytes

Abstract

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 (Vmax) 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 Vmax 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 Vmax. 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 woman.

Erythrocyte sodium/potassium ATPase activity in severe preeclampsia

“…SP activity in the latter group was increased compared with non-pregnant, normotensive women, in agreement with some,10–14 but not all,14–17 previously published studies. Previous estimates of erythrocyte SP function in preeclampsia using direct measurements as opposed to indirect surrogates, such as transport rate constant, intracellular sodium concentration or number of ouabain-binding sites, have also been inconsistent, showing increased,16–18 decreased19,20 or unchanged12,15,21–23 activity. This heterogeneity is unlikely to be entirely explained by differences in methods, as no correlation between results and technique is obvious.…”

Radioimmunoassay of plasma ouabain in healthy and pregnant individuals

“…Circulating endogenous cardiac glycoside-like compounds also link the sodium pump to vascular changes. In pregnant women, the lymphocyte sodium pump density and activity (Ang et al 1990) and the erythrocyte sodium pump rate and activity (MacPhail et al 1992, Yoshimura et al 1993 have been found to be greater than in non-pregnant individuals. In contrast, the amount of the 2 subunit of the sodium pump in the myometrium is smaller in pregnant than in non-pregnant women (Maxwell et al 1998).…”

Red Cell Deformability in Gestational Hypertension

“…This finding is in agreement with previous papers [27][28][29][30][31], Another component may be the reduced erythrocyte deformability. Red cell deformability and survival [16,32] in gestational hypertension basically depends on three clearly defined properties, namely, the geometry of the cell (mostly unchanged), the state of the interior of the cell (dehydrated with HjO loss and altered electrolyte transport) [33][34][35][36], and the state of the mem brane (increase of the cholesterol/phospholipid ratio). It is clear that all these factors are associated and contribute to the altered properties of red blood cells and their prema ture destruction to different extents.…”