Increased fetoplacental active renin production in pregnancy-induced hypertension

Since pregnancy-induced hypertension is associated with impaired uteroplacental blood flow, we studied fetoplacental and maternal renin production in controls and subjects with pregnancy-induced hypertension. We measured total, active, and inactive (pro-) renin in maternal serum, fetal arterial and venous blood, and chorion homogenate in eight normotensive term patients and 18 patients with pregnancy-induced hypertension. No differences in active or prorenin were found in maternal blood from normal women or patients with pregnancy-induced hypertension. In contrast, fetal artery and vein, as well as chorionic tissue, contained significantly higher active renin in pregnancy-induced hypertension compared with normal subjects. No difference in fetal or chorionic prorenin was seen in the two groups. Thus active to total renin ratio was higher in the fetus and chorion of subjects with pregnancy-induced hypertension, which suggests enhanced active renin production. These results suggest that pregnancy-induced hypertension is associated with increased activity of the renin-angiotensin system in the fetoplacental unit, which is not reflected in the maternal circulation. This may be an attempt by the fetus and chorionic membranes to maintain vascular homeostasis in the face of altered uteroplacental blood flow.