Endocrine regulation of LIF has been investigated in vitro in a few species and in vivo in the sheep and mouse, but no work has been published on the effects of hormones on LIF expression in a carnivore. In the skunk, PRL is the primary pituitary hormone responsible for initiating increased luteal activity and induction of blastocyst implantation. In our experiments, blood PRL concentration exceeded the normal physiologic range during the periim-plantation period. The dose employed was equivalent to that used previously to induce implantation without adverse effects; however, the dose had no significant effect on the abundance of LIF mRNA when compared to that in the ovariectomized controls or in intact females whose uteri contained blastocysts in diapause. The duration of PRL treatment used in this study was less than half that required to renew blastocyst development and induce early implantation. Consequently, we cannot rule out the possibility that a more prolonged exposure to elevated PRL could affect LIF expression. antibiotics levaquin
Ovarian steroids are required for some changes in the skunk uterus that occur during the periimplantation period. Estrogen is required for development of tall columnar luminal epithelium, and progesterone stimulates uterine protein synthesis. However, elevated plasma estrogen concentration inhibits uterine protein synthesis in this species. Blood levels of estrogen are high and fluctuate considerably during embryonic diapause, but they decline during resumption of blastocyst development.