Development of Nonovulatory Antral Follicles in Heifers: Changes in Steroids in Follicular Fluid and Receptors for Gonadotr opins*

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Abstract
The objective of this study was to examine changes in steroid concentrations in follicular fluid (FF) and in gonadotropin receptors in nonovulatory follicles that develop after ovulation in heifers. Six groups of six to seven heifers were ovariectomized on days 3,5,7,9,11, and 13 of an estrous cycle. Follicles 6 mm or more in diameter were separated into two classes, estrogen-active (E-A) and estrogen-inactive (E-I). E-A follicles had higher concentrations of estradiol than progesterone and androgens in FF and a low incidence of atresia. E-I follicles had higher concentrations of progesterone or androgens than estradiol in FF and a high incidence of atresia. Diameters, numbers of granulosa cells, and capacities of granulosa cells and thecal tissue to bind [125I]iodo-hCG increased in E-A follicles from days 3–7. During this time, diameters, numbers of granulosa cells, concentrations of estradiol, and capacities of granulosa cells and thecal tissue to bind gonadotropins were greater in EA than E-I follicles. On days 9,11, and 13, each heifer had only a single E-I follicle. Compared with E-A follicles on day 7, E-I follicles on days 9,11, and 13 were smaller and had less granulosa cells, less estradiol in FF, and a lower capacity to bind [125I]iodohCG. After day 7, E-A follicles were not observed until day 13. We conclude that at least two periods of growth and atresia of follicles occur between days 3–13 of an estrous cycle in heifers. One is during days 3–7 when a single E-A follicle 6 mm or more in diameter develops and all other E-I follicles regress. The other is between days 7 and 13 when the E-A follicle from day 7 becomes an E-I follicle and regresses, and another E-A follicle develops.