Placental vascularization in middle and late gestation in the pig

Abstract

The aims of this study were to determine the changes in the capillary area density in relation to fetal development, to determine immunoexpression of angiogenic factors and to compare their mRNA expression throughout pig gestation. Samples were collected from the maternal-chorioallantoic interface at days 40, 77, 85 and 114 of pregnancy for immunohistochemistry analysis and the measurement of mRNA expression of VEGFA, ANGPT1, ANGPT2, FGF2 and its receptors KDR, TEK, FGFR1, FGFR2 respectively. Morphometric measurement of blood vessels was performed. We found a significant increase in capillary area density throughout gestation (P < 0.05). On the maternal side, at day 77, we observed a significant increase in the number of vessels from small vascular areas (P < 0.05) and the vascular area was significantly higher on day 85 (P < 0.05). On the fetal side, the number of vessels and the vascular area increased between days 40 and 77 (P < 0.05) and between days 77 and 114 (P < 0.05), respectively. Immunohistochemical findings revealed intense VEGFA staining and a trend for increased expression towards the end of gestation (P < 0.05). We also demonstrated a high VEGFA, FGF2, FGFR1, ANGPT1 and ANGPT2 mRNA expression at day 77 (P < 0.05). In conclusion, our findings suggest that an active angiogenesis would be present even until late-middle gestation at day 77 of pregnancy with the predominance of angiogenic stimulation by VEGFA/KDR, FGF2/FGFR1 and a balance between ANGPT1 and ANGPT2/TEK.