Alterations in follicular steroid hormones during the preovulatory period in the ewe

Progesterone, testosterone and estradiol-17 beta were quantified within the thecal layer, granulosal layer and fluid of the preovulatory follicle and in ovarian and jugular venous sera of sheep. Prior to the preovulatory surge of luteinizing hormone (LH), the total content of estradiol-17 beta was elevated within each follicular constituent. These levels diminished rapidly to minimal values concurrent with the surge of LH. Follicular tissue and fluid contents of testosterone were low at all times, but were higher before the surge of LH and subsequently (like estradiol-17 beta) declined. The initial decrease in follicular estradiol-17 beta occurred before the first detected decline in testosterone. Changes in sera concentrations of estradiol-17 beta in the ovarian vein draining the ovary with the preovulatory follicle or in the jugular vein were similar to follicular variations in estradiol-17 beta. Likewise, changes in concentrations of testosterone in ovarian venous sera were indicative of follicular changes. Testosterone was undetectable in jugular venous sera. During the period leading up to the anticipated time of ovulation, and approximately 8 h after follicular testosterone and estradiol-17 beta had fallen, content of progesterone within thecal tissue, granulosal tissue and follicular fluid increased. Alterations in follicular progesterone were not reflected by hormone changes in either ovarian or peripheral sera.