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.