Maternal regulation of embryonic growth: The role of vasoactive intestinalpeptide

Vasoactive intestinal peptide (VIP) is an important growth regulator of the embryonic day (E)9-E11 mouse. In comparably aged rat embryos, VIP messenge r RNA (mRNA) is not detectable; however, peak concentrations of VIP in mate rnal rat serum indicate a nonembryonic source. In the current study, mouse maternal and embryonic tissues were examined from E6-E12. Although RT-PCR r evealed VIP mRNA in E6-E7 conceptuses, by E8 (when extraembryonic tissues c ould be separated from the embryo), VIP mRNA was detected only in the decid ua/trophoblast. Decidual/trophoblastic VIP mRNA decreased until E10, after which it was not detectable. VIP mRNA was not apparent in the embryo until E11-E12. At E9, VIP immunoreactivity was localized to abundant, diffuse cel ls in the decidua basalis, which were also immunoreactive for T cell marker s. VIP binding sites were dense in the decidua/trophoblast at E6, but gradu ally decreased until E10, after which they were not apparent. VIP binding s ites were detected in embryonic neuroepithelium by E9. The transient presen ce of VIP binding sites and mRNA in the decidua/trophoblast correlate with the critical period of VIP growth regulation, when VIP mRNA is absent in th e embryo. These findings suggest that maternal lymphocytes are the source o f VITP's regulating early postimplantation embryonic growth.