Pregnancy induced hypertension and sodium pump function in erythrocytes

Erythrocyte sodium/potassium ATPase activity in severe preeclampsia

OBJECTIVE

Elevated blood levels of endogenous digitalis-like factors (EDLF) may decrease erythrocyte sodium pump activity in preeclampsia. As the highest EDLF levels might be expected in severe preeclampsia, we investigated sodium pump activity in that group of patients.

STUDY DESIGN

Erythrocyte sodium pump activity was determined by (86)Rubidium uptake (in nM per hour per 10(6) cells) in women with severe preeclampsia and those with normal pregnancies, matched for gestational age, and in healthy nonpregnant women (n=12 in each group). Differences between groups were analyzed by a two-sided Student t-test.

RESULT

Sodium pump activity was significantly increased in normotensive pregnancies as compared with normotensive non-pregnant women (81.4+/-8.4 vs 61.1+/-7.4, mean+/-s.d., p<0.05), and was decreased 43% in severe preeclamptic pregnancies as compared with normotensive pregnancies (46.4+/-14.1 vs 81.4+/-8.4, p<0.05).

CONCLUSION

Severe preeclampsia is associated with significantly lower erythrocyte sodium pump activity than normotensive pregnancy. These data suggest that plasma levels of a biologically active EDLF are elevated in patients with severe preeclampsia.

Platelet sodium pump and sodium potassium cotransport activity in nonpregnant, normotensive, and hypertensive pregnant women

OBJECTIVE

To determine ouabain-sensitive sodium pump and bumetanide-sensitive sodium potassium cotransport activity in platelets from nonpregnant and normotensive pregnant women and from women with pregnancy-induced hypertension (PIH).

METHODS

Blood was collected from 9 normotensive nonpregnant subjects, 24 normotensive pregnant subjects in both second and third trimesters, 9 subjects who developed proteinuric PIH, and 9 subjects who developed moderate nonproteinuric PIH. Platelet sodium pump activity was determined by the difference in the uptake of rubidium-86 in the presence and absence of ouabain; sodium potassium cotransport (SPC) activity is that component that is inhibitable by bumetanide.

RESULTS

SPC activity was similar in normotensive subjects in the second [median (range) 78 mmol Rb/h/mg protein (18-140)] and third trimesters [85 (39-134)] but was significantly (p < 0.001) higher than in nonpregnant subjects [22 (4-107)]. In addition, SPC was significantly (p < 0.001) lower in subjects with nonproteinuric [42 (4-67)] or proteinuric PIH [59 (33-102)] compared to those who remained normotensive. Sodium pump activity was significantly higher (p < 0.05) in nonpregnant subjects [263 (188-430)] compared with the other groups of subjects. Total rubidium uptake was significantly higher (p < 0.05) in third-trimester normotensive subjects [471 (243-560)] compared with second-trimester subjects [405 (278-608)].

CONCLUSION

Our results suggest that the lower SPC activity in both nonproteinuric and proteinuric PIH may be an early sign of abnormality in the transport of sodium and potassium across the vascular smooth-muscle cell membrane, which is responsible for the maintenance of blood pressure.

The Na+/K+ co-transport system in erythrocytes from pregnant patients

In erythrocytes, the extrusion of a cellular sodium level load is accomplished by the Ouabain--sensitive Na+/K+ pump and by the furosemide-sensitive Na+/K(+)--cotransport, which operates against the passive sodium permeability. An abnormal low rate of net sodium extrusion by the Na+/K+ cotransport was observed in pre-eclamptic patients. At the molecular level the cotransport abnormality seems to be the consequence of an apparent diminished affinity for intracellular Na+. Normal pregnancy is characterized by a strong increase of Na+/K+ cotransport efflux. No difference could be detected between the passive sodium permeability of erythrocytes from normotensive pregnant patients and from normotensive non-pregnant controls. Pre-eclampsia seems to be associated with a low passive sodium and potassium permeability. The abnormalities of cotransport and red cell deformability in patients with pre-eclampsia might be interpreted as an early sign of impaired microcirculation and increased vascular reactivity.