Oestrogens and progestagens in rat ovarian follicles during the oestrous cycle

The amounts of follicular oestrogens increased simultaneously with the growth of follicles to reach a maximum on the day of pro-oestrus at 18:00 h, then decreased rapidly. Progestagens were detectable only in large follicles excised at pro-oestrus. Small follicles at pro-oestrus contained small amounts of oestrogens.