Characterization of Insulin-Like Growth Factor-Binding Proteins in the Uterus and Conceptus during Early Conceptus Elongation in Cattle¹

^a Animal Reproduction and Biotechnology Laboratory Colorado State University, Fort Collins, Colorado 80523–1683 ^b USDA-ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska 68933–0166

As a first step in determining the role that insulin-like growth factor (IGF)-binding proteins (BPs) may have in regulating initial stages of conceptus elongation in cattle, the type and relative abundance of IGFBPs in serum, uterine tissues, and uterine fluid from pregnant and noninseminated cows on Days 13 and 15 postestrus and in Day 15 conceptuses was evaluated. Uterine and serum samples contained IGFBPs 2, 3, 4, and 5 as determined by immunoprecipitation followed by Western ligand blots of precipitates. Compared with those in uterine and serum samples, IGFBPs in conceptuses and conceptus-conditioned culture media were only faintly detectable. The percentage of the total IGF-I binding activity attributed to IGFBP-3 was greater (p < 0.05) in myometrium, serum, and uterine fluid (> 50%) than in inter- (40%) and intracaruncular (37%) endometrium. Percentage of total binding attributed to IGFBP-2 was greater (p < 0.05) in endometrium and serum (~30%) than in myometrium (16%) and uterine fluid (9%). Binding activity of certain IGFBPs varied due to day of the estrous cycle or due to pregnancy status. Concentrations of IGF-I in serum were greater (p < 0.05) in nonpregnant (52 ± 2 ng/ml) than in pregnant (40 ± 4 ng/ml) cows. Concentration of IGF-I in uterine fluid did not differ due to pregnancy status or stage of cycle (4.4 pg IGF-I/µg uterine protein). Northern blots revealed mRNAs for IGFBPs 1, 2, 3, 4, and 5 in uterine tissues but not in conceptuses. In situ hybridization indicated that IGFBP-1 mRNA was primarily localized in luminal epithelium of endometrium; IGFBP-2 mRNA was in luminal epithelium and dense stromal cells adjacent to endometrial epithelium; and IGFBP-3 mRNA was in vascular endothelial cells and was more prevalent in myometrium than in endometrium. Tissue specificity and changes in abundance of IGFBPs in the uterus during early conceptus elongation indicate the potential importance of IGFBP regulation of uterine IGFs during this time period.

¹ This research was supported in part by NIH grant No. R01-HD27938 and the Colorado State University Experiment Station through Regional Project W-171. M.L.K. was a trainee on USDA Grant No. 90–38420–5242. Mention of trade names is necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.

² Correspondence: A.J. Roberts, USDA-ARS, U.S. Meat Animal Research Center, P.O. Box 166, Clay Center, NE 68933–0166. FAX: (402) 762–4382; roberts{at}email.marc.usda.gov

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