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Growth and Differentiation of Large Antral Follicles after Spontaneous Luteolysis in Heifers: Changes in Concentration of Hormones in Follicular Fluid and Specific Binding of Gonadotropins to Follicles¹

Michigan State University, East Lansing 48824 and and Agricultural Institute, Grange, Ireland

² Anim. Sci. Dept. Author to whom reprint request should be sent.

Abstract

The objective of the present study was to characterize changes in growth, concentrations of steroids in follicular fluid (FF) and gonadotropin receptors of individual antral follicles after spontaneous luteolysis in heifers and to reexamine our hormonal method of classifying healthy and atretic follicles. Groups of heifers were ovariectomized (OVX) before regression of corpora lutea on d 17, 18 and 19 of an estrous cycle and after regression of corpora lutea at time periods before, during and after preovulatory gonadotropin surges. Each follicle 6 mm in diameter was examined for concentration of progesterone, androstenedione, testosterone and estradiol-17β in FF and capacities of granulosal and thecal cells to specifically bind ¹²⁵I-bovine follicle stimulating hormone (bFSH) or ¹²⁵I-human chorionic gonadotropin (hCG). Follicles were separated into two classes, estrogen-active (E-A) or estrogen-inactive (E-I). Concentrations of estradiol in FF were higher than both progesterone and androgens in E-A follicles, whereas either androgens or progesterone was higher than estradiol in E-I follicles. Diameters, volumes of FF and numbers of granulosal cells in E-A follicles increased from d 17 through the end of the preovulatory gonadotropin surges. During this time, concentrations of progesterone, androstenedione and estradiol in FF and specific binding of ¹²⁵I-hCG to granulosal and thecal cells increased, whereas specific binding of ¹²⁵I-bFSH to granulosal cells decreased. In E-I follicles, progesterone in FF decreased and androstenedione increased from d 17 through end of gonadotropin surges. The E-I follicles had a higher incidence of granulosal cells with pycnosis than E-A follicles. We concluded that changes in growth, concentration of steroids in FF and gonadotropin receptors in E-A follicles after spontaneous luteolysis were similar to changes we previously reported for E-A follicles after prostaglandin-induced luteolysis, and that ratio of concentration of estradiol in FF to both progesterone and androgens could be used to separate potential ovulatory (E-A) from atretic (E-I) follicles in heifers.

¹ We gratefully acknowledge members of Agriculture Institute, Grange, Ireland, especially Don Kinsley, Dan Prendiville and Aiveen McArther for their round-the-clock support in this research. We kindly thank Dr. Gavin Cheng, Univ. of Manitoba, Canada, for donation of bFSH; NICHHD for gift of hCG, bLH and bFSH; Dr. Gordon Niswender, Colorado State Univ., for donation of androstenedione antisera. We also wish to thank Leon Spicer, Larry Chapin and Clyde Anderson for assistance in computer analysis and members of the Anim. Reprod. Laboratory for critique of our manuscript. This research was supported by NSF Grant PC 7904571. An abstract of some of these data was presented at the 73rd Annu. Meet, of the Amer. Soc. of Anim. Sci., July 26-29, 1981, North Carolina State Univ., Raleigh. This manuscript is published with permission of the Michigan State Agr. Exp. Sta. Director as journal article 10421.

³ Agricultural Institute, Grange, Ireland. Present address: Vet. Field Sta., Ballycoolin Rd., Finglas, Dublin II.

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