|Roberts, Andrew - Andy|
Submitted to: Endocrine Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2001
Publication Date: 4/1/2001
Citation: ROBERTS, A.J., FUNSTON, R.N., MOSS, G.E. INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS IN THE BOVINE ANTERIOR PITUITARY. ENDOCRINE JOURNAL. 2001. V. 14(3). P. 399-406. Interpretive Summary: A cascade of hormones that are produced and act within the hypothalamus, pituitary gland and gonad controls reproduction. The metabolic hormone, insulin-like growth factor-1 (IGF-1) and IGF binding proteins (IGFBPs) may act with in the pituitary as a component regulating this hormonal cascade. Objectives of the current study were to characterize the specific IGFBPs in nbovine anterior pituitary tissue, during the time around ovulation. Treatments of pituitary tissue with LHRH, a hormone from the hypothalamus, and two steroids, estradiol or progesterone, produced by the ovary were also evaluated. The predominant IGFBPs produced and released by anterior pituitary tissue during the periovulatory period were IGFBP-2, -3 and -5. Levels of these IGFBPs in pituitary tissue decreased from the preovulatory through the postovulatory period. Treatment of pituitary tissue with LHRH increased release of IGFBP-2. Estradiol or progesterone did not alter IGFBPs. Observations that IGFBP declined throughout the periovulatory period and LHRH stimulated secretion of IGFBP-2 implicate IGFBPs as potential regulators of reproduction.
Technical Abstract: Insulin-like growth factor binding proteins (IGFBPs) were characterized in bovine anterior pituitary tissue, pituitary conditioned media and serum collected during the periovulatory period. In vitro treatments of pituitary tissue with LHRH, estradiol, or progesterone were also evaluated. Predominant IGFBPs detected in anterior pituitary tissue by immunoprecipitation, ligand blotting, and Northern blotting were IGFBP-5 (29 kDa), IGFBP-2 (32 kDa), and IGFBP-3 (36 and 39 kDa doublet). Conditioned culture media contained IGFBP-5, a slightly larger form of IGFBP-2 (33 kDa), the 36- and 39-kDa forms of IGFBP-3 as well as a more extensively glycosylated form of IGFBP-3 (44 kDa). In serum, IGFBP-5 was not readily detected, and IGFBP-3 (40- and 44-kDa doublet) and IGFBP-2 (34 kDa) were larger than in pituitary tissue. Levels of IGFBP-2, -3, and -5 in pituitary tissue decreased from the preovulatory through the postovulatory period. Treatment with LHRH increased IGFBP-2 levels in media twofold. Estradiol or progesterone did not alter IGFBP secretion in vitro. Predominant IGFBPs produced and released by anterior pituitary tissue during the periovulatory period were IGFBP-2, -3 and -5. Observations that these IGFBPs declined throughout the periovulatory period and secretion of IGFBP-2 was stimulated by LHRH implicate IGFBPs as potential regulators of gonadotrope function.