Development of Antral Follicles in Cattle after Prostaglandin-Induced Luteolysis: Changes in Serum Hormones, Steroids in Follicular Fluid, and Gonadotropin Receptors*

Abstract

Changes in growth, concentrations of steroids in follicular fluid, and numbers of gonadotropin receptors in follicles 6 mm or more in diameter were examined 12, 24, 36, 48, 60, and 72 h after prostaglandin (PG)-induced luteolysis in heifers. Follicles with higher concentrations of estradiol than progesterone and androgens in follicular fluid (FF) were classified as estrogen active (E-A). Follicles with higher concentrations of progesterone or androgens than estradiol in follicular fluid were classified as estrogen inactive (E-I). Although E-A and E-I follicles were similar in size 12–72 h after PG treatment, before the preovulatory surge of LH, numbers of granulosa cells, estradiol concentrations, and capacities of follicles to specifically bind gonadotropins were markedly lower in E-I follicles. Most E-I follicles had histological signs of atresia, whereas E-A follicles did not. Sizes, concentrations of steroids in FF, and specific binding of gonadotropins to follicle cells did not change in E-A or E-I follicles 12- 72 h after PG treatment but before the preovulatory surge of LH. However, diameters of E-A follicles were highly correlated with concentrations of estradiol and progesterone in FF and with capacities of granulosa and thecal cells to specifically bind [¹²⁵I] iodo-hCG. In contrast, diameters of E-A follicles were highly negatively correlated with concentrations of testosterone in FF and with capacities of granulosa cells to specifically bind [¹²⁵I] iodobovine FSH. We conclude that E-I follicles are atretic and E-A follicles are potentially ovulatory follicles. In addition, after a single injection of PG during an estrous cycle in heifers, the growth and differentiation of ovulatory follicles were not synchronized.