Nonluteal source of lordosis-promoting progesterone secretion in guinea pigs

Prepubertal (21-24 days of age), intact female guinea pigs treated sequentially with estradiol benzoate and LH or FSH displayed lordosis behavior. The gonadotropins apparently caused release of progesterone from the ovaries, because lordosis behavior in guinea pigs is activated by sequential action of estrogen and progesterone. These data demonstrate that immature ovaries, completely devoid of corpus luteum tissue, are capable of secreting behaviorally significant concentrations of progesterone when stimulated by gonadotropins. Therefore, the luteal compartment of the guinea pig ovary is not essential for the preovulatory surges of progesterone that coincide with expression of lordosis behavior in adulthood. Likely candidates for sources of preovulatory progesterone in prepubertal females are antral follicle and interstitial gland tissue.