LEUKEMIA INHIBITORY FACTOR IN ENDOMETRIUM DURING THE ESTROUS-CYCLE, EARLY-PREGNANCY AND IN OVARIECTOMIZED STEROID-TREATED EWES

Leukaemia inhibitory factor (LIF), a pleiotropic cytokine, is essentia l for blastocyst implantation in mice and maintains the development of ovine embryos in culture. The expression of LIF was examined by north ern blot analysis in endometrial tissue from cyclic (days 4-16) and pr egnant (days 4-20) ewes, and the corresponding protein was immunolocal ized. Expression of mRNA encoding LIF remained relatively constant thr oughout the oestrous cycle and was present during early pregnancy. A d ecrease in mRNA encoding LIF was observed during early pregnancy (on d ays 12-14) and expression was highest on days 16-20. Immunoreactive LI F was present in the cellular compartments of the endometrium througho ut the oestrous cycle and early pregnancy, with maximal immunostaining in the caruncular and intercaruncular luminal epithelium, and moderat e staining in the glandular epithelium and intercaruncular stroma. Imm unoreactive LIF was also detected in the trophoblast cells of day 17 b lastocysts. Separately cultured endometrial epithelial and stromal cel ls from pregnant animals both expressed mRNA encoding LIF. Ovariectomi zed steroid-treated ewes were studied to establish whether steroid hor mones had a role in regulating endometrial LIF. Ewes treated with oest radiol alone showed lower concentrations of immunoreactive LIF in the endometrium in comparison to ovariectomized, control animals, while tr eatment of ovariectomized animals with both oestradiol and progesteron e had a greater inhibitory effect on LIF immunolocalization. These stu dies demonstrate the presence of mRNA encoding LIF and protein through out the oestrous cycle and early pregnancy and suggest that steroid ho rmones may be involved in their regulation.