Leukemia inhibitory factor (LIF) has been shown to play an important role in the implantation of mouse blastocysts. The present study was designed to investigate the changes of LIF protein, LIF receptor, and gp130 in the mouse uterus during the early pregnancy. LIF protein and LIF receptor were at high levels in the mouse uterus near the time of ovulation and on day 4 of pregnancy. gp130 was highest on days 3 and 4 of pregnancy. Both LIF receptor and gp130 showed strong staining in the stroma of the day 5 uterus, at a time when LIF protein was low. The presence of LIF receptor and gp130 in the luminal epithelium on day 4 and in the stroma on day 5 may indicate the site of the high affinity LIF receptor. The coexistence of a high level of LIF protein, LIF receptor, and gp130 in the day 4 uterus is consistent with the previously observed high level of uterine LIF mRNA on the same day and the importance of LIF for the blastocyst implantation in mouse.

Leukaemia inhibitory factor (LIF) is a pleiotrophic cytokine which plays an obligatory role in mouse implantation. To investigate its potential role in the regulation of uterine function in the human, LIF secretion by isolated human endometrial glandular epithelial and stromal cells in primary culture was determined. Endometrial cells secreted a detectable amount of LIF protein during the first 48 h of culture. In the follicular and late-luteal phases, LIF secretion by both cell types was low. At every stage of the menstrual cycle, the epithelial cells secreted significantly more LIF than did stromal cells. Glandular epithelial cells of the mid-luteal phase, at the expected time of implantation in the human, secreted significantly more LIF than at other stages of the cycle. Stromal cells showed a similar, but nonsignificant, LIF secretion pattern. It could be concluded that endometrial LIF expression was dependent on cell type and stage of the menstrual cycle, and might thus play a role in human implantation. Oestradiol-17 beta stimulated both prostaglandin (PG) F and E release by the epithelial cells in both follicular and luteal phases. PGE release during the luteal phase was greater than in the follicular phase. However, addition of recombinant human LIF did not change either PGF or PGE release in either follicular or luteal phases, in the presence or absence of oestradiol.

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Leukemia inhibitory factor (LIF) has been shown to play an important role in the implantation of mouse blastocysts. The present study was designed to document the appearance of LIF in the rabbit uterus during early pregnancy and to determine whether changes just prior to implantation, similar to those in mice, occurred. LIF was localized in endometrial epithelium, myometrium, and endometrial glands. A low level of LIF was detected in the uterus of nonestrous and estrous females. LIF expression reached its highest level on day 5 of pregnancy and declined on days 6 and 7. By day 13 of pregnancy, little endometrial LIF was apparent. The expression of LIF on day 5 of pseudopregnancy was similar to that on day 5 of pregnancy. LIF expression was much higher at implantation sites than that at nonimplantation areas on day 7 of pregnancy. It is concluded that LIF may be important for the implantation of rabbit blastocysts.