Acute effects of various gonadotropins and other pituitary hormones on preovulatory ovarian progestin secretion in hypophysectomized rats.

Preovulatory release of progesterone has been well established in various species of mammals. In the rat, a remarkable increase in ovarian progesterone secretion at proestrus was first demonstrated by Eto et al.(1962)and confirmed by other workers (Hashimoto et al., 1968) including ourselves (Uchida et al., 1969). The determination of ovarian progestin secretion and plasma LH level on the same laboratory rats bred under the same condition (Miyake, 1968; Kobayashi et al., 1968; Uchida et al., 1969) has demonstrated that the increase in progesterone secretion at proestrus occurs almost concurrently with an increase in plasma LH level. Furthermore, hypophysectomy at 5.00p.m. of the day of proestrus, the time of which is critical for the release of LH in our rats, interrupts the increase of progesterone secretion (Uchida et al., 1969). These data suggest that the increase of progesterone secretion at proestrus depends on the function of the pituitary, most likely the releasing of LH. In the present experiments, various gonadotropins and other pituitary hormones have been examined to elucidate their acute effects on ovarian progestin secretion in the rats hypophysectomized at 5.00p.m. on proestrus in order to see whether LH is a specific factor responsible for the stimulation of progesterone secretion at proestrus.