RESUMEN
In Iberian pigs, a high conceptus loss occurs during the first 30 days of gestation. Although the exact causes for these losses have not been determined to date, the importance of blood vessel development during early pregnancy has been noted. The aim of this study was to analyze the messenger RNA (mRNA) and protein expression of VEGF-rs (vascular endothelial growth factor, the VEGFR1, and the VEGFR2 receptor system) and elucidate a possible relationship with the conceptus status (healthy or arrested) on gestational Days (gd) 22 and 32. Both mRNA and protein expression for VEGF-rs molecules were consistently expressed in conceptuses and endometrium during the pregnancy period analyzed. In endometrium, a significant increase in VEGF mRNA and VEGFR2 mRNA expression in healthy sites was observed as pregnancy advances (P < 0.001 and P < 0.05, respectively), whereas VEGFR1 mRNA expression was maintained at a constant level. Interestingly, a significantly elevated VEGFR2 mRNA expression (P < 0.05) was observed on gd 22 in endometrium from arrested conceptuses. Furthermore, VEGF mRNA and VEGFR1 mRNA expression in trophoblasts from healthy conceptuses decreased as pregnancy proceeded (P < 0.001). Arrested trophoblasts on gd 32 showed higher VEGFR2 mRNA expression than healthy conceptuses (P < 0.05). Although, in endometrium attachment sites, the pattern of VEGF-rs immunostaning was not affected by conceptus status, the immunoexpression of VEGF-rs in healthy attachment sites increased slightly but consistently as gestation proceeded. In arresting trophoblasts, VEGF and VEGFR2 staining decreased from gd 22 to 32. Moreover, the number of VEGF and VEGFR1-positive capillaries in the subepithelial vascular plexus of endometrium was related to the conceptus status, showing a moderate increase in healthy sites as pregnancy advances. In conclusion, it appears that VEGF-rs is expressed and related to vascular development in Iberian pigs between gd 22 and 32. The upregulated expression of VEGF mRNA and VEGFR2 mRNA in healthy uterine sites suggests a significant role for these angiogenic factors in early pregnancy.
