Dw. Brann et al., EFFECT OF PROGESTERONE ON GALANIN MESSENGER-RNA LEVELS IN THE HYPOTHALAMUS AND THE PITUITARY - CORRELATION WITH THE GONADOTROPIN SURGE, Neuroendocrinology, 58(5), 1993, pp. 531-538
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.