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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #181456
Title: LARGE VARIATION IN STEROID CONCENTRATIONS AND INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS EXISTS AMONG INDIVIDUAL SMALL ANTRAL FOLLICLES COLLECTED FROM WITHIN COWS AT VARIOUS STAGES OF ESTROUS CYCLE

Author
item Roberts, Andrew
item AL-HASSAN, M - KING SAUD UNIVERSITY
item FRICKE, P - U OF WISCONSIN
item Echternkamp, Sherrill

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2006
Publication Date: 10/1/2006
Citation: Roberts, A.J., Al-Hassan, M.J., Fricke, P.M., Echternkamp, S.E. 2006. Large variation in steroid concentrations and insulin-like growth factor binding proteins exists among individual small antral follicles collected from within cows at various stages of estrous cycle. Journal of Animal Science 84:2714-2724.

Interpretive Summary: Successful reproduction in animals is dependant on the capacity of the female to produce a viable oocyte for fertilization. The number of ovarian follicles (the structure in which the oocyte develops) that begin to develop each estrous cycle far exceeds the normal rate of follicles that ovulate, with over 99 percent of follicles dieing before reaching the mature stage. An underlying hypothesis of the present research is that variations in profiles of steroid and certain proteins (Insulin-like growth factor binding proteins: IGFBPs) in individual small follicles present on the ovaries of a cow at any given time may predetermine which follicles are capable of undergoing development to the mature stage when exposed to appropriate hormone signals. A total of 108 small follicles were collected from six cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21 , 5.5 , and 3.5-fold apart for estradiol (E2), progesterone (P4), and androstenedione (A4), respectively, whereas greatest differences between minimum and maximum were 505 , 108 , and 26-fold apart for E2, P4, and A4, respectively. The fold difference between the maximum activities of the 4 different forms of IGFBPs detected in small follicles was 3.8 for IGFBP-3, 8.7for IGFBP-2, 37 for IGFBP-4 and 671 for IGFBP-5. These results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals, and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of small follicle development to the mature stage. A greater understanding of the biochemical process involved in regulating follicular development will expedite the identification of aberrations that result in infertility, and facilitate development of approaches to improve reproductive performance.

Technical Abstract: An underlying hypothesis of the present research is that variations in the biochemical status of individual small (< 5.1 mm diameter) antral follicles present on the ovaries of a cow at any given time determines the capacity for undergoing recruitment, selection and establishing dominance. Objectives were to investigate magnitude of variation in follicular fluid concentrations of steroids and activities of IGFBP among individual small antral follicles within and between cows, and to determine relationships between follicular fluid IGFBP and steroid concentrations in these follicles. A total of 108 small follicles were collected from six cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Ranges in concentrations of steroids (ng/mL fluid) in the overall population of follicles were 0.1 (lowest detectable limit) to 51 for estradiol (E2), 4 to 1149 for progesterone (P4), and 5 to 504 for androstenedione (A4). A positive association existed between concentrations of E2 and A4 (r = 0.23; P < 0.02), but E2 (r = 0.39) and A4 (r = 0.43) were associated negatively with P4. The proportion of variation in steroid concentrations accounted for by differences among animals (P < 0.05) was small for E2 (12%), moderate for P4 (43%) and greatest for A4 (74%). Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21 , 5.5 , and 3.5-fold apart for E2, P4, and A4, respectively, whereas greatest differences between minimum and maximum were 505 , 108 , and 26-fold apart for E2, P4, and A4, respectively. Western ligand blot detection of IGFBP activity in a sub sample of 41 follicles resulted in ranges (arbitrary densitometer units) of 1.18 to 4.50 for IGFBP-3, 0.54 to 4.68 for IGFBP-2, 0.07 to 2.56 for IGFBP-4 and 0.01 to 6.71 for IGFBP-5. Concentrations of E2 were associated negatively with each IGFBP except IGFBP-3. In contrast, concentrations of A4 were associated positively with IGFBP-3, but were not associated with other IGFBP. Concentrations of P4 were associated positively with IGFBP-3, IGFBP-4 and IGFBP-5. These results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals, and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of recruitment.