The present report confirms the expression of GM-CSF in the LE, SG, DG, endometrial vasculature, and isolated cells in the stroma during the estrous cycle in the cow. GM-CSF is secreted in the uterine lumen because it is detectable in flushings from nonpregnant but particularly from pregnant cows. Accordingly, endometrial GM-CSF is up-regulated during pregnancy in both the ewe and the cow, and the moderate stimulation of GM-CSF in the LE after exposure to IFN-т also fits with this expression pattern. GM-CSF is known to stimulate human and murine placen-to-fetal growth, differentiation and survival, in vitro and in vivo. Moreover, GM-CSF promotes development of in vitro-produced bovine embryos and may up-reg-ulate IFN-т production.
Culture of murine embryos with GM-CSF enhances blastocyst formation and attachment, as well as glucose metabolism and viability of the inner cell mass. A similar regimen prevents inner cell mass apoptosis in human embryos. In GM-CSF knock-outs, as expected, resorptions are increased and fetal weights are reduced because of placental dysfunctions, and even postnatal deaths are more frequent. Thus, these present results suggest that the bovine endometrium accommodates the conceptus by providing a powerful growth/ antiapoptotic factor to assist it during the demanding period of elongation and attachment.