Plasma active and inactive renin and fetal complications in women with high risk pregnancies.

To examine whether the activation of the renin system, which occurs during pregnancy, may be relevant for the development and the outcome of the fetus, we measured active and inactive renin throughout gestation in 29 women having a pregnancy defined as "high risk" because of a clinical history of hypertension, nephropathy, and unexplained abortions. In 23 of these women who delivered full-term infants with normal weight and status, we found that active renin increased progressively from early pregnancy until the end of the second trimester and then declined slightly thereafter. In contrast, in the remaining six women who had fetal complications consisting of either signs of distress requiring cesarean section or growth retardation, the increase in active renin failed to occur. In all women the levels of inactive renin were more elevated throughout gestation than those observed in nonpregnant women, and were higher, although not significantly, in women without fetal complications than in those with fetal complications. Thus, a blunted activation of the renin system during pregnancy is associated with alteration in fetal development and may possibly contribute to it.

Comparative measurements of immunoreactive renin, plasma renin activity and angiotensin II in human plasma.

In human plasma samples we compared the values of renin activity, determined with a conventional enzymatic assay, with those of immunoreactive renin, determined with a new, direct immunoradiometric assay which employs highly specific monoclonal antibodies, and with those of angiotensin II; the comparative measurements of renin were carried out also in trypsin activated samples of nephric and anephric subjects. We found that, overall, there was a close relationship between renin activity and immunoreactive renin; however, this relationship was absent when the statistical analysis was restricted to plasmas with low or very low renin. We also found that, within a rather wide range of values, angiotensin II was more closely correlated with immunoreactive renin than with renin activity. Trypsin activation increased to a similar extent immunoreactive renin and renin activity in plasma of nephric and anephric subjects and, overall, the values of total renin obtained with the two assays were significantly correlated. The results of these comparative determinations indicate that, in general, the measurement of immunoreactive renin represents a valid alternative to that of renin activity and a reliable index of the activity of the renin-angiotensin system. In addition, studies with trypsin activation suggest that even in the anephric state human plasma contains an inactive enzyme convertible into an active form which has immunological properties similar to those of active renin.