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-co nverting 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. I n the myometrium., the ACE activity was significantly higher in dioestrous than in oestrous. ACE activity correlated negatively with the day of gestat ion 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 par t of the basal zone. In the intercotyledonary membrane and the placentome, the mesenchymal cells located near the trophoblast cells expressed ACE. Sol itary macrophage- or monocyte-like cells showing intense renin immunoreacti vity were found in the uterus, while the uterine and the glandular epitheli al cells displayed inconsistent reactivity. No renin was observed in the pl acentomes or in the fetal membranes. The findings demonstrate a regulated e xpression of angiotensin-forming enzymes throughout the bovine uteroplacent al unit. Whether this local renin-angiotensin system contributes to the hig hly regulated morphological and functional changes throughout the oestrous cycle and gestation remains to be established. (C) 2001 Harcourt Publishers Ltd.