A study of alpha-human atrial natriuretic peptide in normal pregnancy and in pre-eclampsia

The object of this study was to compare plasma levels of alpha-human atrial natriuretic peptide (ANP) in patients with pre-eclampsia, normal pregnant women, and healthy non-pregnant women. This was an observational study carried out at Llandough Hospital, Cardiff, Wales on 85 age-matched women divided into three groups (30 patients with pre-eclampsia, 30 healthy pregnant women in the third trimester and 25 healthy non-pregnant women). Plasma ANP concentration was measured between 14.00 and 16.00 hours, in the recumbent position using pre-extraction radioimmunoassay. The following measurements were also performed: blood urea, serum creatinine, serum uric acid and serum sodium in all study subjects and 24-hour urinary protein in pregnant women. All women were eating a normal diet. It was shown that plasma ANP levels were significantly higher in healthy pregnant women in the third trimester of pregnancy than in non-pregnant women (18.12 +/- 7.36 vs. 13.68 +/- 6.41 pmol/l, P < 0.05). This difference was also observed in pre-eclamptic women (17.6 +/- 12.06 pmol/l vs. 13.68 +/- 6.41 pmol/l, P < 0.05) but the plasma hormone levels were not significantly different from healthy pregnant women. In all pregnant women, plasma ANP level was related to the gestational age and birth weight as shown by the regression coefficient (+ 0.39,-0.26 respectively, P < 0.05). In pre-eclamptic patients, there was no relationship between the severity of hypertension, assessed by the level of systolic and diastolic blood pressure, serum uric acid level and amount of proteinuria, and log (plasma) ANP levels. There was a significant negative correlation between serum sodium level and log (plasma) ANP level in all pregnant subjects (r=- 0.51, P < 0.05). Compared with non-pregnant women, plasma ANP levels are increased during the third trimester of normal pregnancy and in pregnancies complicated by pre-eclampsia. A relationship between ANP and pre-eclampsia seems unlikely but ANP is probably involved in the regulation of sodium and water balance in normal pregnancy and in pre-eclampsia.