Inhibition of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the granulosa cells of mouse ovarian follicles by follicular fluid peptide

A protein fraction (GF2) was purified from sheep ovarian follicular fluid. Its action on 3 beta-HSD activity in the mouse granulosa cells was measured in an in vitro system. The fraction (GF2) caused dose-dependent depletion of the 3 beta-HSD activity in granulosa cells and progesterone in the spent medium. A maximum inhibition of the activity was achieved after 30 min incubation of the granulosa cells with the GF2 fraction. Further purified HPLC fraction (Fr1) also inhibited 3 beta-HSD activity. In vivo administration of the GF2 fraction in normal cycling female mice also decreased the 3 beta-HSD activity in the granulosa cells of the ovarian follicles and plasma progesterone levels indicating the GF2 fraction to be a 3 beta-HSD inhibitor.