Characterization of proliferative activity in bovine placentomes between day 150 and parturition by quantitative immunohistochemical detection of Ki67-antigen

In order to characterize proliferative activity in bovine placentomes, the expression of the proliferation marker Ki67-antigen was investigated immuno histochemically at days 150, 220, 240, 270 of gestation and at parturition (n = 3 animals/group). The percentage of Ki67-antigen-positive cells ([%Ki6 7(+)]) was determined for the caruncular stroma cells (CS), caruncular epit helium (CE), trophoblast (T) and stromal cells of chorionic villi (fetal st roma, FS). The proliferation pattern as indicated by [%Ki67+] was substanti ally different (p < 0.0001) between the four cell categories with the highe st 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 c oefficient: -0.056%/day; p < 0.01) and for CS (p < 0.02) with a nonlinear t rend (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 res ults suggest that the continuous high proliferation of CE is partly indepen dent from total caruncular growth and may therefore also serve the permanen t tissue remodeling and the compensation of the destructive activity of wea kly invasive trophoblast giant cells, and that proliferation of CS is trans iently suppressed between days 150 and 270 of gestation. An involvement of placental oestrogens in the control of proliferation in CE and CS is sugges ted.