Angiotensin-converting enzyme activity in the bovine uteroplacental unit changes in relation to the cycle and pregnancy

The expression of the angiotensin-forming enzymes, renin and angiotensin-converting enzyme (ACE), were examined in the bovine uteroplacental unit. The ACE activity was determined in cell membrane fractions, and ACE and renin were localized by autoradiography and immunohistochemistry, respectively. In the myometrium, the ACE activity was significantly higher in dioestrous than in oestrous. ACE activity correlated negatively with the day of gestation in the endometrium and myometrium but positively in the placentome and allantoamniotic membrane. Autoradiography showed, that ACE was localized in vascular endothelial cells in all compartments. ACE was also expressed in the endometrial stroma and uterine glands, most pronounced in the outer part of the basal zone. In the intercotyledonary membrane and the placentome, the mesenchymal cells located near the trophoblast cells expressed ACE. Solitary macrophage- or monocyte-like cells showing intense renin immunoreactivity were found in the uterus, while the uterine and the glandular epithelial cells displayed inconsistent reactivity. No renin was observed in the placentomes or in the fetal membranes. The findings demonstrate a regulated expression of angiotensin-forming enzymes throughout the bovine uteroplacental unit. Whether this local renin-angiotensin system contributes to the highly regulated morphological and functional changes throughout the oestrous cycle and gestation remains to be established.