RELATIONSHIPS BETWEEN CONCENTRATIONS OF OVARIAN-STEROIDS, INSULIN-LIKE GROWTH-FACTOR-I AND IGF-BINDING PROTEINS DURING FOLLICULAR DEVELOPMENT IN THE EWE

The objective of the present study was to determine how insulin-like g rowth factor-1 (IGF-1) and IGF-binding proteins (IGFBPs) are related t o in vivo follicular development in the sheep, Oestrus was synchronise d in 20 cyclic ewes and the animals were slaughtered 44 h after the se cond injection, just before the start of preovulatory luteinising horm one (LH) surge. Normal growing follicles were dissected from the ovari es of each ewe and their diameters measured. The follicular fluid was aspirated and assayed for oestradiol, testosterone and total IGF-1 con tent, The follicles were classified as either non-oestrogenic or oestr ogenic if the follicular fluid content of oestradiol was less than 60 ng ml(-1) or more than 60 ng ml(-1), respectively. The mean diameter o f oestrogenic follicles was significantly (P < 0.001) higher than that of non-oestrogenic ones, but testosterone concentrations did not diff er, IGF-1 concentrations in oestrogenic follicles were significantly ( P < 0.01) lower than those in non-oestrogenic ones, with a significant (P < 0.01) negative correlation between follicular oestradiol content and IGF-1 concentration. IGFBPs were identified by Western ligand blo t analysis using 12% sodium dodecyl sulphate polyacrylamide gel electr ophoresis under non-reducing conditions and band intensities on autora diographs were quantified by scanning densitometry, The intensity of t he doubler of IGFBP at 44-42 kDa was significantly (P < 0.02) higher i n follicular fluid from oestrogenic follicles, whereas the intensity o f the band at 35 kDa was significantly (P < 0.001) higher in follicula r fluid from non-oestrogenic follicles. Some of the non-oestrogenic fo llicles also exhibited bands at 32.0-28.5 kDa with variable intensitie s, but such bands were totally absent in oestrogenic follicles. The re sults of this study suggest an involvement of both IGF-1 and IGFBPs in ovine follicular development.