Vasoactive intestinal peptide influences hatching of ovine blastocysts

Abstract

Expanded blastocysts collected from superovulated Sarda ewes were divided at random into four groups for culture in a simple medium that does not support blastocyst hatching (CZB) or a complex medium that is permissive to hatching (TCM 199), with or without vasoactive intestinal peptide (VIP), a known embryo mitogenic peptide. Plasminogen activator (PA) secretion after 24 h of culture, and the number of cells, diameter of blastocysts and hatching rate after 48 h of culture were compared. The results showed an increase in hatching rate (78.6 v. 6.7%; P<0.01), diameter and number of cells (220.89 v. 210.44 m, P<0.01 and 246 v. 232, P<0.01 respectively) and caseinolytic areas (1.33 v. 0.92 cm, P<0.01) of blastocysts cultured in TCM 199 compared with those cultured in CZB. Supplementation of the culture media with VIP increased these parameters in CZB (P<0.01) and partially in TCM 199. In particular, cell number, diameter and PA activity were significantly higher (P<0.01) after culture with VIP in both media. Immunoneutralization of exogenous VIP in culture with anti-VIP antibody caused a decrease in the hatching rate (P<0.01) of embryos cultured in medium with VIP, similar to the rate in unsupplemented CZB (P<0.01). These results suggest a receptor-mediated response. In immunohistochemical studies, VIP was shown to bind receptors in hatched blastocysts demonstrating the VIP–receptor interaction, and VIP receptors of approximately 150 kDa were revealed by electrophoretic studies. In conclusion, ovine preimplantation embryos exhibit VIP receptors, providing a basis for a receptor-mediated influence of VIP in the hatching of ovine blastocysts.