VIP regulation of embryonic growth.

Vasoactive intestinal peptide (VIP) plays a regulatory role in the growth of early postimplantation rodent embryos through its action on receptors localized to the central nervous system (CNS). However, the origin of the VIP influencing embryonic growth is unknown. VIP binding sites have been found prenatally; however, VIP mRNA was not detected in the rat CNS before birth and has been detected in peripheral organs only during the final third of gestation. Recent studies have revealed that VIP receptors were limited to the CNS in the embryonic day 11 (E11) rat embryo/trophoblast, which, in addition, had almost four times the VIP concentration of the E17 fetus. However, neither in situ hybridization or reverse transcriptase-polymerase chain reaction methods detected VIP mRNA in the E11 rat embryo or embryonic membranes. Rat maternal serum revealed a peak in VIP concentration at days E10-E12 of pregnancy, with VIP levels 6- to 10-fold higher than later during pregnancy. Radiolabeled VIP, administered intravenously to pregnant female mice, was found in the E10 embryo. These results suggest that VIP produced by extraembryonic tissues may regulate embryonic growth during the early postimplantation stage of development in the rodent.