[Effect of gonadotropin releasing hormone agonist (Gn-RHa) on steroidogenesis in human and rat ovaries].

The effects of Gn-RHa on rat granulosa cells and on human granulosa and luteal cells were examined. (I) In rat granulosa cells: 1) Gn-RHa inhibited the stimulating effect of PMSG on progesterone and estradiol production. 2) In a tracer experiment, Gn-RHa inhibited PMSG-stimulated progesterone production by stimulating 20 alpha-hydroxyprogesterone production. On the other hand, Gn-RHa inhibited estradiol production by inhibiting PMSG-stimulated aromatization. 3) On 20 alpha-hydroxysteroid dehydrogenase activity, it appears that Gn-RHa accelerates the maximum velocity and decreases the affinity of the enzyme to 20 alpha-hydroxyprogesterone as the substrate. (II) In man: 1) In granulosa cells during the ovulatory phase, Gn-RHa inhibited PMSG-stimulated progesterone and estradiol production. 2) In luteal cells, Gn-RHa inhibited hCG-stimulated progesterone production. 3) The affinity of Gn-RH receptor in the corpus luteum was lower than that in rat ovaries. These results suggest that in the human ovary as well as in the rat ovary, Gn-RHa might have a direct effect on the development of the follicle.