EFFECT OF PROGESTERONE ON GALANIN MESSENGER-RNA LEVELS IN THE HYPOTHALAMUS AND THE PITUITARY - CORRELATION WITH THE GONADOTROPIN SURGE

Galanin has been shown to be an important neuropeptide associated with the preovulatory surge of gonadotropins. Since the preovulatory surge of gonadotropins is induced by the action of estrogens and progestero ne, the present study examined the effect of estrogens and progesteron e on hypothalamic and pituitary galanin mRNA levels. Galanin mRNA was present as the 900-base pair message in the hypothalamus and the pitui tary. In the 27-day-old ovariectomized immature rat, treatment with 2 mug of estradiol for 2 days did not bring about any changes in hypotha lamic galanin mRNA levels. In adult rats, ovariectomy also did not bri ng about any changes in hypothalamic galanin mRNA levels. However, 14 days of estradiol replacement increased hypothalamic galanin mRNA leve ls. Progesterone treatment in the estrogen-primed ovariectomized immat ure rat resulted in a significant increase in hypothalamic galanin mRN A levels at 12:00 and 14:00 h. This increase occurred at the time of t he initiation of the progesterone-induced LH and FSH surges. Estrogen treatment enhanced pituitary galanin mRNA levels which were further in creased by progesterone treatment at 12:00 h, the time of the initiati on of the gonadotropin surge by progesterone. In the PMSG-primed immat ure rat, pituitary galanin mRNA levels were increased due to ovarian e strogen and progesterone secretion as a result of PMSG treatment. Pitu itary galanin mRNA levels were decreased by the anti-progestin RU486 a t 12:00 and 20:00 h, times that coincided with a decrease in serum LH by RU486 as compared to the PMSG-treated controls. Thus, galanin is an important neuropeptide that acts at the level of the hypothalamus and the pituitary in modulating the gonadotropin surge and is regulated b y progesterone in both tissues.