ACTIVITY OF ERYTHROCYTE SODIUM-HYDROGEN EXCHANGE IN NORMAL-PREGNANCY

1. Pregnancy is associated with a 30-50% rise: in cardiac output and a 50% increase in blood volume. The contribution of changes in the acti vity of primary and secondary active transporters to these haemodynami c adaptations remains unknown. For the first time, we measured sodium- hydrogen exchange activity over the course of normal pregnancy. 2. Eig hteen healthy pregnant women were studied at 14, 24 and 33 weeks. of g estation and compared with 18 non-pregnant healthy women. None of the pregnancies was complicated by hypertension. At each antenatal visit, body weight and blood pressure were recorded, blood and 24 h-urine sam ples were taken to control renal function and metabolic equilibrium, m aternal glucose tolerance was evaluated by oral glucose test and glyca ted haemoglobin testing, and erythrocyte sodium-hydrogen antiport was also measured. 3. Erythrocyte antiport activity values were 10.0 +/- 3 .0, 9.6 +/- 2.9 and 8.4 +/- 3.5 mmol h(-1) (litre of cells)(-1) in the three gestational trimesters respectively, significantly higher at ea ch trimester than in control women [6.8 +/- 2.5 mmol h(-1) (litre of c ells)(-1)]. The clearances of urea and creatinine were constantly elev ated in pregnant women; at each trimester their serum concentrations w ere lower than in non-pregnant women. Serum potassium significantly de creased during pregnancy. Serum total cholesterol and triacylglycerol levels, already above the normal range from the first trimester, furth er increased until the third trimester. The area under the glycaemic c urve became larger during pregnancy, and the area under the insulinaem ic curve increased to a lesser extent. There was al significant associ ation between antiport activity and serum triacylglycerol levels. 4. T he observed hyperactivity of the transporter, peaking at the fourteent h week of gestation, may be a contributing factor to the haemodynamic adjustments attending upon normal pregnancy.