NA,K-ATPASE FROM PLACENTA OF WOMEN WITH PREGNANCY-INDUCED HYPERTENSION EXHIBITS AN INCREASED AFFINITY FOR CARDIAC-GLYCOSIDES

Microsomes were prepared from placentas of normotensive women and of p atients suffering from pregnancy induced hypertension (PIH). Activity of Na,K-ATPase (estimated as ATP hydrolysis) from the hypertensive tis sue was lower than from tissue of normotensive women, even if the numb er of Na,K-ATPase molecules (monitored by anthroyl ouabain binding) wa s actually greater in the hypertensive tissue. The affinity of Na,K-AT Pase for anthroyl ouabain was about four times higher in plasma membra nes of hypertensives, indicating some structural change in the Na,K-AT Pase or in its vicinity. Assuming the presence of an endogenous digita lis-like factor, the results suggest a simple way of explaining not on ly the lower Na,K-ATPase activity in the placental membranes of hypert ensives but also the different extent of enzyme inhibition in differen t tissues of PIH patients.