The aim of this study was to examine whether differences in placental
angiotensinase A (
glutamyl aminopeptidase, EC 3.4.11.7) activities occurred in hypertensive complications of pregnancy compared with uncomplicated pregnancies. Biochemical and semiquantitative histochemical methods were used and compared for their applicability.
Angiotensinase A activity was detected using L-alpha glutamyl-4-methoxy-2-naphthylamide (alpha-Glu-MNA) as substrate and
Fast Blue B salt for simultaneous azo-coupling in cryostat sections of placental tissue samples from 32 patients with
pre-eclampsia, 11 patients with
pregnancy-induced hypertension and 44 participants with uncomplicated pregnancies. The graduated intensity of reaction product in the villous trophoblast and in fetal blood vessels was evaluated semiquantitatively in a double-blind study by light microscopy (semiquantitative score method). Score levels were related to relative frequencies of hypertensive disorders (proportional odds model) and correlated to the severity of
gestational hypertension (Spearman's rank correlation). After detection of
enzyme activity, the same tissue samples were homogenized and used for kinetic fluorometric measurements under the same substrate and
buffer conditions as in
enzyme histochemistry. Enhanced villous trophoblastic
angiotensinase A activity was significantly associated with an increased frequency of
pre-eclampsia in pregnant women (cumulative odds ratio x 0(1) 6.37; P < 0.001) and showed significant correlations with the severity of gestational hypertensive disorders, represented by systolic (r = 0.31; P < 0.05) and diastolic (r = 0.34; P < 0.05 blood pressure and by concomitant
proteinuria (r = 044; P < 0.01). Histochemical evaluation of fetal blood vessels and biochemical measurements revealed no statistically significant results. In conclusion this study demonstrates for the first time that increased villous trophoblastic
angiotensinase A activity indicates an increased likelihood of the presence of
pre-eclampsia and the severity of hypertensive disorders in pregnancy.