Journal of Animal Science, Vol 80, Issue 1 179-190, Copyright © 2002 by American Society of Animal Science

EVALUATION STUDIES

Changes in follicular fluid steroids, insulin-like growth factors (IGF) and IGF-binding protein concentration, and proteolytic activity during equine follicular development

T. S. Bridges, T. R. Davidson, C. S. Chamberlain, R. D. Geisert and L. J. Spicer
Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.

The objective of the present study was to evaluate changes in equine follicular fluid insulin-like growth factor binding protein (IGFBP) proteolytic activity as well as steroid, IGF, and IGFBP concentrations during follicular development in the mare. Mares (n = 14) were classified as either in the follicular phase (n = 8) or luteal phase (n = 6). Follicles (n = 92) were categorized as small (6 to 15 mm; n = 54), medium (16 to 25 mm; n = 23), or large (> 25 mm; n = 15), and follicular fluid was collected. Estradiol and androstenedione levels in follicular fluid were greater (P < 0.05), and IGFBP-3 concentrations tended to be greater (P < 0.10) in large than in small or medium follicles, whereas IGFBP-2, -4, and -5 levels were less (P < 0.05) in large than in small or medium follicles. Estradiol and androstenedione concentrations were negatively correlated (P < 0.01) with IGFBP-2, -4, and -5 but not IGFBP-3 concentrations. To evaluate proteolysis of IGFBP, follicular fluid was incubated with human 125I-labeled IGFBP-2, -3, and -5 and protein separated by 12% SDS-PAGE. Follicular fluid caused little or no proteolysis of 125I-lableled IGFBP-2 or -3, and the small amount of proteolysis of IGFBP-2 and -3 did not differ (P > 0.10) among follicle classes. However, more 125I-labeled IGFBP-5 was cleaved (P < 0.05) by follicular fluid from large follicles collected during the follicular phase than large follicles during the luteal phase, and small or medium follicles from follicular and luteal phase mares indicating that a protease to IGFBP-5 exists in estrogen-dominant equine follicles. This IGFBP-5 protease was inhibited by kallikrein/serine protease and metalloprotease inhibitors. We conclude that the tendency of estrogen-dominant follicles of mares to have greater levels of IGFBP-3 and lesser levels of IGFBP-2 does not appear to be due to differences in proteolysis, whereas changes in IGFBP-5 levels are likely due to changes in activity of a serine protease or metalloprotease. Changes in IGFBP may alter levels of bioavailable IGF that stimulate steroidogenesis and mitogenesis in developing mare follicles.

This article has been cited by other articles:

				M A Beg and O J Ginther Follicle selection in cattle and horses: role of intrafollicular factors. Reproduction, September 1, 2006; 132(3): 365 - 377. [Abstract] [Full Text] [PDF]

				O J Ginther, E L Gastal, M O Gastal, and M A Beg In vivo effects of pregnancy-associated plasma protein-A, activin-A and vascular endothelial growth factor on other follicular-fluid factors during follicle deviation in mares Reproduction, April 1, 2005; 129(4): 489 - 496. [Abstract] [Full Text] [PDF]

				E D Watson, S-E Bae, R Thomassen, S R M Thomson, K Woad, and D G Armstrong Insulin-like growth factors-I and -II and insulin-like growth factor-binding protein-2 in dominant equine follicles during spring transition and the ovulatory season Reproduction, September 1, 2004; 128(3): 321 - 329. [Abstract] [Full Text] [PDF]

				L. J. Spicer Proteolytic Degradation of Insulin-Like Growth Factor Binding Proteins by Ovarian Follicles: A Control Mechanism for Selection of Dominant Follicles Biol Reprod, May 1, 2004; 70(5): 1223 - 1230. [Abstract] [Full Text] [PDF]

				O.J. Ginther, E.L. Gastal, M.O. Gastal, and M.A. Beg Critical Role of Insulin-Like Growth Factor System in Follicle Selection and Dominance in Mares Biol Reprod, May 1, 2004; 70(5): 1374 - 1379. [Abstract] [Full Text] [PDF]

				S. E. Echternkamp, A. J. Roberts, D. D. Lunstra, T. Wise, and L. J. Spicer Ovarian follicular development in cattle selected for twin ovulations and births J Anim Sci, February 1, 2004; 82(2): 459 - 471. [Abstract] [Full Text] [PDF]

				O.J. Ginther, D.R. Bergfelt, M.A. Beg, C. Meira, and K. Kot In Vivo Effects of an Intrafollicular Injection of Insulin-Like Growth Factor 1 on the Mechanism of Follicle Deviation in Heifers and Mares Biol Reprod, January 1, 2004; 70(1): 99 - 105. [Abstract] [Full Text] [PDF]

				G. M. Rivera and J. E. Fortune Selection of the Dominant Follicle and Insulin-Like Growth Factor (IGF)-Binding Proteins: Evidence that Pregnancy-Associated Plasma Protein A Contributes to Proteolysis of IGF-Binding Protein 5 in Bovine Follicular Fluid Endocrinology, February 1, 2003; 144(2): 437 - 446. [Abstract] [Full Text] [PDF]

				T. R. Davidson, C. S. Chamberlain, T. S. Bridges, and L. J. Spicer Effect of Follicle Size on In Vitro Production of Steroids and Insulin-Like Growth Factor (IGF)-I, IGF-II, and the IGF-Binding Proteins by Equine Ovarian Granulosa Cells Biol Reprod, June 1, 2002; 66(6): 1640 - 1648. [Abstract] [Full Text] [PDF]