Consequently, the importance of LIF in renewing blastocyst development or implantation in the skunk remains unclear. In other species, addition of recombinant LIF to embryos results in an increased rate of blastocyst formation and survival in vitro. If the function of LIF is similar in the skunk, then uterine LIF concentration might be expected to correlate with the proportion of viable embryos present in the uterus. In our study, dead or dying blastocysts were recovered from all ovariectomized progesterone-treated animals, from 57% of the estradiol-treated skunks, from 29% of those treated with progesterone and estrogen, and from 43% of the ovariec-tomized control animals receiving only diluent. None of the ovariectomized PRL-treated animals contained dead or dying blastocysts. Despite these differences in blastocyst viability, LIF mRNA concentration did not significantly differ between the hormone treatment groups. This lack of correlation between blastocyst viability and uterine LIF concentration suggests that for the spotted skunk, embryo viability in vivo is dependent upon PRL and ovarian hormones rather than uterine LIF expression. proventil inhaler
In summary, LIF mRNA is present in the uterus of the spotted skunk throughout delayed implantation, increases at the time of renewed embryo development, and remains detectable in the uterine glands for up to 72 h postattachment. Immunoreactive LIF protein is up-regulated in the luminal and glandular epithelium during the early stages of embryo activation and appears in the uterine lumen during periimplantation. Although these changes in uterine LIF expression are consistent with our initial hypothesis and occur concurrently with precise changes in the endocrine environment, LIF mRNA appears to be regulated by factors other than PRL, progesterone, or estradiol. The function and regulation of LIF expression during the periimplanta-tion period in the spotted skunk remain unknown.