Blood vessels number, endothelial vascular growth factor, induced nitric oxide synthase and endothelial nitric oxide synthase expression in the ovine allantois

The number of blood vessels and the percentage of allantoic mesenchymal cells immunochemically expressing vascular endothelial growth factor (VEGF), induced nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) were calculated during early gestation in sheep. The percentages of VEGF, iNOS and eNOS drastically diminished between 28 and 35 d of gestation, and the number of blood vessels augmented (P < 0.01). There were statistically significant differences among animals at the same gestational age for all calculated values, which might imply a genetic influence for vascular development, as reported in other species. The whole population of mesenchymal cells does not participate in vasculogenesis. There was not trophoblastic VEGF expression, but eNOS was more intensely expressed than iNOS. In conclusion, in order to have a successful vascular development in the allantois it appears that VEGF, iNOS and eNOS must be expressed which could provoke liberation of nitric oxide thus enhancing the angiogenic factor function, to favour embryonic viability.