ERYTHROCYTE SODIUM-LITHIUM COUNTERTRANSPORT IN NORMAL AND HYPERTENSIVE PREGNANCY - RELATION TO HEMODYNAMIC-CHANGES

Objective To establish the changes in erythrocyte sodium lithium count ertransport (SLC) with advancing normal pregnancy and to determine if these changes were different in pregnancy induced hypertension (PIH). The changes in both groups were assessed in relation to haemodynamic c hanges. Design SLC, mean arterial pressure (MAP), cardiac output (CO) and total peripheral vascular resistance (TPVR) were determined serial ly during normal pregnancy and cross-sectionally in PIH. Women were st udied again 20 weeks after delivery where possible. Setting Routine an tenatal clinic and antenatal ward of a regional reference centre. Subj ects Fifty-one normal primigravid women were studied serially and 41 p rimigravid women with PIH were studied at time of diagnosis. Results D uring normal pregnancy SLC (mmol Li/h/l cells) increased from a nonpre gnant value of 0.24 +/- 0.02 (mean +/- SEM) to 0.32 +/- 0.02 at 14 wee ks, and 0.37 +/- 0.02 at 20 weeks gestation. This was maintained until 38 weeks (0.40 +/- 0.02). The increase until 20 weeks occurred at the time of greatest change in CO (5.10 +/- 0.18 to 6.79 +/- 0.20 l/min) and TPVR (1327 +/- 58 to 969 +/- 33 dyn/s/cm-5). The decrease in TPVR with a rise in SLC is opposite to the relation reported in essential h ypertension so that a functional relation is unlikely. However, the ch anges within pregnancy were positively correlated (r = 0.43, P<0.01). In hypertensive pregnancies TPVR was elevated compared with normotensi ve pregnancies (1543 +/- 100 vs 1090 +/- 37) but the SLC was not diffe rent from that found in normotensive pregnancies (0.43 +/- 0.02 vs 0.4 0 +/- 0.02). Conclusions The changes in SLC activity suggest dynamic e ffects on erythrocyte membrane function during pregnancy. However, no differences could be found between normal and hypertensive pregnancy a nd SLC is unlikely to be of value as a marker of hypertensive risk dur ing pregnancy.