Characterization of Proliferative Activity in Bovine Placentomes Between Day 150 and Parturition by Quantitative Immunohistochemical Detection of Ki67-Antigen

Abstract

Contents In order to characterize proliferative activity in bovine placentomes, the expression of the proliferation marker Ki67-antigen was investigated immunohistochemically at days 150, 220, 240, 270 of gestation and at parturition (n = 3 animals/group). The percentage of Ki67-antigen-positive cells ([%Ki67 + ]) was determined for the caruncular stroma cells (CS), caruncular epithelium (CE), trophoblast (T) and stromal cells of chorionic villi (fetal stroma, FS). The proliferation pattern as indicated by [%Ki67 + ] was substantially different (p < 0.0001) between the four cell categories with the highest proliferation rates in CE (58.0 ± 6.9 to 68.3 ± 5.7), followed by CS (10.6 ± 3.4 to 45.3 ± 5.4), T (23.3 ± 3.4 to 25.4 ± 4.7) and FS (2.9 ± 0.4 to 10.5 ± 1.7). Influence of gestational age between days 150 and 270 was significant for FS (p < 0.01) with a linear trend (regression coefficient: -0.056%/day; p < 0.01) and for CS (p < 0.02) with a nonlinear trend (p < 0.05) which was described by a polynomial model: y = 220 - 1.96x + 0.0046x 2 with y = [%Ki67 + ] and x = day of gestation (p < 0.05). The results suggest that the continuous high proliferation of CE is partly independent from total caruncular growth and may therefore also serve the permanent tissue remodeling and the compensation of the destructive activity of weakly invasive trophoblast giant cells, and that proliferation of CS is transiently suppressed between days 150 and 270 of gestation. An involvement of placental oestrogens in the control of proliferation in CE and CS is suggested.