Direct determination of plasma renin concentration during pregnancy: comparison with renin enzymatic activities

A solid phase sandwich assay for human renin was used to determine the total renin concentration in plasma throughout the course of a normal pregnancy. These values were compared with the enzymatic activity of renin, with and without trypsin treatment. Plasma concentration of immunoreactive renin rapidly increased four fold from 214 +/- 33 pg/ml (in non-pregnant subjects) within a few weeks after conception and remained high up to the third trimester. Total renin concentration, estimated by trypsin-activated enzyme activity showed similar changes, both qualitatively and quantitatively. A positive correlation (r = 0.63, p less than 0.001) between immunoreactive renin concentration and its enzymatic activity was noted whereas the active renin concentration did not positively correlate with the immunoreactive renin concentration. These data indicate that solid phase sandwich assay for human renin should be a pertinent tool to elucidate the role of the renin-angiotensin system in pregnancy.