Steroid hormone concentrations in the fluid of bovine follicles relative to size, quality and stage of the oestrus cycle.

Eight hundred and seven bovine antral follicles from 2 mm to 20 mm in diameter were dissected free of stromal tissue, measured, qualified and divided into 36 groups according to size, quality and stage of cycle. The follicular fluid was collected and assayed by RIA for oestradiol-17beta, testosterone and progesterone. The steroid hormone concentrations vary with follicular size, degree of atresia and stage of the cylce. Non-atretic follicles of less than 8 mm are generally androgen-dominated and non-atretic follicles of more than 11 mm are oestrogen-dominated. Follicles betwen 8 mm and 11 mm are intermediate in this respect. Degeneration leads to a gradual decrease of oestradiol-17beta and testosterone concentration and increase of progesterone. It is suggested that the ratio of oestradiol-17beta/testosterone and oestradiol- 17beta/progesterone and oestradiol-17beta/testosterone + progesterone cannot generally be used to discriminate between non-atretic and atretic follicles. Large follicles present during the early luteal stage contain as much oestradiol-17beta in the follicular fluid as large follicles during the follicular stage, whereas large follicles of the luteal stage contain only 15% of the maximal amount of the latter's. This and other presented data support the statement that follicles present during the early luteal, late luteal and follicular stages of the cycle belong to different groups of growing follicles. It has been concluded that groups of macroscopically qualified follicles can be distinguished from each other by the steroid hormone concentration in the follicular fluid. It is therefore possible to predict the hormonal environment of the oocyte in any individual follicle of a defined size and quality.