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

The activity of erythrocyte sodium-proton exchanger in women with pregnancy- induced hypertension

BACKGROUND

Hypertension that develops after 20 gestational weeks and is defined as pregnancy-induced hypertension (PIH). The main cause of PIH is vasoconstriction and the thickening of vascular media, which decreases vascular capacity and increases peripheral resistance. One of the theories postulated to explain this phenomenon is that a transmembrane sodium transport disorder causes an increase in intracellular sodium concentration. In the latest literature, special attention is paid to the role of the increased intracellular sodium concentration in the pathogenesis of essential hypertension (EH). One of the best documented phenotypes for EH is the increased activity of the sodium-proton exchanger (NHE). The aim of this study was to assess if increased NHE activity could be the mechanism responsible for the development of PIH.

SUBJECTS AND METHODS

The study included 30 women: 10 pregnant women with PIH after gestational week 30, 10 women with physiological pregnancy after 30 gestational weeks, and 10 healthy non-pregnant women. NHE activity was determined according to Orlov's method as amiloride-sensitive H(+) efflux from acid-loaded cells.

RESULTS

The NHE activity in the group of women with PIH was significantly higher than that in women with physiological pregnancy: 10.09 +/- 1.65 vs. 6.81 +/- 2.3 mmol/L RBC/h (p < 0.049) and in the group of non-pregnant women: 10.09 +/- 1.65 vs. 7.56 +/- 1.66 mmol/L RBC/h (p < 0.029). Erythrocyte NHE activity did not differ in the group of women with physiological pregnancy and in the group of non-pregnant women.

CONCLUSION

These results seem to suggest that erythrocyte NHE activity is elevated in PIH pregnancies.

Neutrophil intracellular pH and Na+/H+ exchanger activity in pre-eclampsia

Elevated Na(+)/H(+) exchanger activity and intracellular acidosis have previously been demonstrated in white blood cells isolated from women who have suffered from a pre-eclamptic pregnancy. The mechanisms underlying this abnormality and the implications in pre-eclamptic pregnancies are, at present, unclear. In this study, we used neutrophils from third trimester pre-eclamptic patients and third trimester normotensive pregnant controls to determine Na(+)/H(+) exchanger isoform-1 (NHE-1) activity and intracellular pH. This was performed using a well-validated technique involving flurometry and a pH sensitive dye, 2,7'Bis-(carboxyethyl) 5.6 carboxyfluorescein acetomethyl ester (BCECF-AM). Time course experiments were performed to assess the contribution of plasma factors to intracellular pH measurements. Plasma digoxin-like factor (DLF) was assessed in both patients and normotensive controls. Neutrophil intracellular pH was significantly lower in the pre-eclamptic patients (7.15 +/- 0.050) compared with the normotensive pregnant controls (7.36 +/- 0.027; P<.001). NHE-1 activity (in mmol/L/min) was significantly higher in the pre-eclamptics (32.4 +/- 1.9) compared with the normotensive neutrophils (27.1 +/- 1.6; P =.038). Times course experiments showed that mean pre-eclamptic intracellular pH increased from 7.11 +/- 0.049 to 7.25 +/- 0.043 after 2 hours of incubation. DLF, measured as amount of inorganic phosphate liberated from adenosine triphosphate (ATP), was significantly lower when plasma from the pre-eclamptic patients was incubated with the enzyme compared with plasma from the normotensive pregnant women (54.9 +/- 2.6 nmol/mL plasma v 63.91 +/- 1.7 nmol/mL plasma, n = 6, P =.018 unpaired Student's t test). The results suggest that elevated NHE-1 activity and intracellular acidosis are intermediate phenotypes in women who have pre-eclampsia. Intracellular pH may have been affected by plasma as shown in the time course experiments. DLF, an inhibitor of Na(+)/K(+)ATPase, may contribute to this intracellular acidosis in pre-eclamptic neutrophils.

Leucocyte intracellular pH and Na+/H+ exchanger isoform-1 activity in postpartum women with pre-eclampsia

OBJECTIVE

To investigate leucocyte Na+/H+ exchanger isoform 1 activity in postpartum pre-eclamptics.

DESIGN

Exchanger isoform-1 activity and intracellular resting pH were established in leucocytes isolated from two study groups.

SAMPLE

Leucocytes isolated from 10 women who had had pre-eclamptic pregnancies more than five months postpartum, and from 10 age-matched normotensive women who were more than five months postpartum.

SETTING

Hypertension Clinic, Antenatal Assessment Area, Leicester Royal Infirmary.

METHODS

A well validated technique involving flurometry using a pH sensitive dye (BCECF-AM) was performed to determine exchanger isoform-1 activity and intracellular pH. Determination of exchanger isoform-1 protein abundance was performed by western blotting. Exchanger isoform-3 protein abundance was examined to rule out the possibility of activity due to this particular isoform.

RESULTS

Intracellular pH was significantly lower in the postpartum pre-eclamptic group (7.11 +/- 0.02), compared with the postpartum normotensive controls (7.33 +/- 0.04; P < 0.001). Exchanger isoform-1 efflux rate (in mmol/L/minute) was significantly higher in the postpartum pre-eclamptic group (35.91 +/- 3.1), compared with the postpartum normotensives (23.94 +/- 2.0; P = 0.005). Exchanger isoform-1 protein density was established to be similar among the two subject groups. No exchanger isoform-3 protein was identified by western blotting.

CONCLUSION

Our results suggest that elevated exchanger isoform-1 activity is an important finding in women who have suffered from pre-eclampsia. This increased activity is not due to an increase in exchanger isoform-1 protein abundance or the presence of exchanger isoform-3.