Abstract:
Transcriptional regulation of insulin-like growth factor binding protein-3(IGFBP-3) by oestrogen was investigated by Northern blot hybridization ofendometrial tissue mRNA from anoestrous ewes treated with oestradiol-17βat either 0, 40 or 80 µg per day for 7 days. The 2.6 kb IGFBP-3transcript, seen in control animals, was virtually undetectable in treatedanimals. This suppressive effect was reflected in Western ligand blots of theuterine luminal fluid (ULF) proteins where the concentration of IGFBP-3 wassignificantly decreased with increasing oestrogen treatments. IGFBP-2 levelswere increased with oestradiol treatment but no significant effect was seen onthe other minor IGFBP’s present in the ULF. Northern analysis alsoshowed that the IGFBP-3 transcript was present from days 12 to 16 of theoestrous cycle but was either absent or very weak on days 0 (oestrus) and 9 ofcycling ewes. In situ hybridization of endometrialtissue sections localized the IGFBP-3 mRNA to the luminal epithelial celllayer, areas of the stromal tissue and in some glandular epithelial cells.Oestradiol treatment of ewes down-regulated expression of IGFBP-3 in theendometrium; therefore, the low levels of IGFBP-3 in ULF during the early partof the oestrous cycle is possibly due to elevated levels of plasma oestradiolaround oestrus.