EFFECTS OF GROWTH-HORMONE AND PREGNANCY ON EXPRESSION OF GROWTH-HORMONE RECEPTOR, INSULIN-LIKE GROWTH-FACTOR-I, AND INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-2 AND PROTEIN-3 GENES IN BOVINE UTERUS, OVARY, ANDOVIDUCT

The effects of growth hormone (GH) and pregnancy on insulin-like growt h factor (IGF)-I, IGF binding protein (IGFBP)-2, and IGFBP-3 mRNA in r eproductive tissues were studied in cattle. Lactating dairy cows were inseminated at estrus and treated with 25 mg/day GH (n = 8) or saline (n = 8) for 16 days. Corpus luteum (CL), ovary (CL removed), oviduct, endometrium, and myometrium were collected at the end of treatment. Me ssenger RNA for GH receptor, IGE-I, IGFBP-2, IGFBP-3, and actin were m easured by nuclease protection assays. The CL contained more GH recept or mRNA than the other reproductive tissues examined. Expression of IG E-I mRNA was highest in myometrium, with lower amounts found in endome trium; the CL expressed the least amount of IGE-I mRNA. The IGFBP-2 mR NA was most abundant in endometrium and least abundant in CL. Expressi on of IGFBP-3 mRNA was detected in all reproductive tissues examined. However, endometrium, a tissue that expressed the most IGFBP-2 mRNA, h ad the lowest amount of IGFBP-3 mRNA. The GH receptor mRNA was decreas ed in cows treated with GH whereas the mRNA for IGF-I, IGFBP-2, or IGF BP-3 was not changed. In the reproductive tissues evaluated, cows that contained a conceptus at tissue collection (pregnant) had higher amou nts of IGF-I mRNA than did nonpregnant cows. In summary, the level of mRNA encoding CH receptor, IGF-I, IGFBP-2, and IGFBP-3 varied within t he tissues examined, suggesting that these genes may play a variety of roles in the bovine female reproductive tract. Supplemental GH failed to change the expression of IGF-I, IGFBP-2, and IGFBP-3 mRNA, possibl y because of low GH receptor mRNA levels in tissues other than CL. A d irect action of GH on IGF-I, IGFBP-2, or IGFBP-3 gene expression withi n cow reproductive tissues was not supported because the amount of ICF -I, IGFBP-2, or IGFBP-3 mRNA was not altered by GH.