ALTERATIONS IN ERYTHROCYTE CHLORIDE CONTENT ACCOMPANYING THE CHANGES IN ERYTHROCYTE HYDRATION AND POTASSIUM CONTENT IN NORMAL HUMAN-PREGNANCY - A COMPARISON WITH PREGNANCY-INDUCED HYPERTENSION

Objectives To determine whether the change in erythrocyte potassium co ntent in normal human pregnancy is accompanied by a similar change in erythrocyte chloride content. To assess erythrocyte hydration and pota ssium and chloride content in pregnancies complicated by proteinuric p regnancy induced hypertension. Design A serial study during and after normal pregnancy. A comparative study during and after pregnancies com plicated by proteinuric pregnancy induced hypertension (PIH). Erythroc yte hydration, total osmoles, potassium and chloride and plasma osmola lity were determined. Setting University teaching hospital, UK. Subjec ts Twenty-eight women studied at 14,28 and 36 weeks of normal pregnanc y and ten women with PIH studied during the third trimester of pregnan cy. All women were reinvestigated 20 weeks after delivery. Results The fall of erythrocyte potassium early in normal pregnancy (277.4 vs 265 .2 mmol/kg; P<0.02) and its rise between 28 and 36 weeks (272.3 vs 288 .0 mmol/kg; P<0.005) were accompanied by similar changes in erythrocyt e chloride content (151.9 vs 131.1 mmol/kg; P<0.001 and 129.4 vs 141.3 mmol/kg; P<0.001, respectively). Plasma osmolality in PIH was raised above that normal in pregnancy (287.2 vs 283.0 mosm/kg; P<0.005). In P IH, compared to normal pregnancy, erythrocyte hydration (2.00 vs 1.89 l/kg dry weight cells), total osmoles (573.0 vs 534.2 mosm/kg), potass ium (303.0 vs 288.0 mmol/kg) and chloride (154.9 vs 141.3 mmol/kg) wer e greater. Conclusions These findings further support the hypothesis t hat changes in plasma osmolality in pregnancy are secondary to alterat ions in cell osmoles and serve to limit changes in cell hydration. Ery throcyte composition and plasma osmolality are altered in PIH.