Changes in concentrations of estradiol were subtle and must be interpreted with caution. In prepubertal female cattle, however, the hypothalamus is exquisitely sensitive to estradiol feedback inhibition of LHRH-induced LH secretion, so differences, even though subtle, may have important physiological implications. As hypothesized, the concentration of estradiol decreased over the 24 h after follicular aspiration, indicating that removal of all follicles a 4 mm in diameter decreased ovarian estrogen synthesis. However, this post-aspiration decrease in the concentration of estradiol was not acute but gradual over the 24 h after follicular aspiration.
It is possible that aspiration of ovarian follicles did not immediately disrupt the ability of the gran-ulosal cells to synthesize and release estradiol. Granulosal cells that remained in aspirated follicles may have undergone a gradual loss of steroidogenesis, which could explain why there was a gradual decrease in the concentration of estradiol over the 24 h after follicular aspiration. The decrease in the concentration of estradiol after removal of all follicles a 4 mm in diameter and the subsequent increase in the concentration of estradiol during the growth period for follicles a 5 mm support previously reported data that follicles begin to have larger quantities of mRNA for aromatase when sizes of 4-5 mm in diameter are achieved.