ESTRADIOL INCREASES RELATIVE AMOUNTS OF INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEIN (IGFBP)-3 IN SERUM AND EXPRESSION OF IGFBP-2 IN ANTERIORPITUITARIES OF EWES

This study determined whether estradiol regulates insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBPs) in the pituitary glan d, hypophyseal stalk median eminence (SME), and circulation concomitan tly with effects on LH. Ovariectomized ewes received an estradiol impl ant or no implant during the anestrous season and were slaughtered 80 days later. Estradiol suppressed serum LH to a greater extent during a nestrus than after onset of the breeding season (Days 60 and 75). Amou nts of mRNA for LH beta subunit were decreased by estradiol, but mRNA for alpha and FSH beta subunits were not affected. Estradiol increased serum IGF-1, IGFBP-3, and IGFBP-4 throughout the treatment period, bu t it did not influence other IGFBPs in serum. In response to estradiol , pituitary IGFBP-2 tended to increase and mRNA for IGFBP-2 increased twofold. Other IGFBPs in the pituitary glared were plea influenced by estradiol. In the SME, IGFBP-2, IGFBP-5, and the 40-kDa IGFBP-3 were i ncreased by estradiol. Thus, estradiol influences both the IGF and gon adotropin systems in sheep, Estradiol influences on gonadotroph functi on may be mediated by alterations in the IGF system.