REGULATION OF ANTERIOR-PITUITARY GONADOTROPIN SUBUNIT MESSENGER-RNA LEVELS DURING THE PREOVULATORY GONADOTROPIN SURGE - A PHYSIOLOGICAL-ROLE OF PROGESTERONE IN REGULATING LH-BETA AND FSH-BETA MESSENGER-RNA LEVELS
Dw. Brann et al., REGULATION OF ANTERIOR-PITUITARY GONADOTROPIN SUBUNIT MESSENGER-RNA LEVELS DURING THE PREOVULATORY GONADOTROPIN SURGE - A PHYSIOLOGICAL-ROLE OF PROGESTERONE IN REGULATING LH-BETA AND FSH-BETA MESSENGER-RNA LEVELS, Journal of steroid biochemistry and molecular biology, 46(4), 1993, pp. 427-437
In a previous study we demonstrated that in the ovariectomized estroge
n-primed immature rat, progesterone induced a gonadotropin surge while
the gonadotropin mRNA subunit levels were either suppressed or unalte
red. This observation has now been confirmed using more frequent time
points. Progesterone administered at 0900 h was found to suppress LH-b
eta mRNA levels at 1300, 1400, and 0800 h the next day, with no subseq
uent effects at 1000, 1200 or 1600 h. FSH-beta mRNA levels were unaffe
cted by progesterone except for a slight elevation at 1400 h and a sup
pression at 0800 h. Progesterone was either suppressive or had no effe
ct on alpha mRNA levels. Since elevations in LH-beta and FSH-beta mRNA
levels were observed in the cycling rat, the observed differences in
the ovariectomized estrogen-primed rat could be due to a higher basal
synthesis occurring due to ovariectomy. This was indeed the case becau
se LH-beta and FSH-beta mRNA levels were 3.7- and 42.7-fold higher in
such animals as compared to intact estrogen-primed rats. In contrast t
o the ovariectomized estrogen-primed rats, in intact estrogen-primed r
ats LH-beta mRNA levels were increased at 1000 h and FSH-beta mRNA lev
els were increased at 1000, 1200 and 1300 h after the administration o
f progesterone. In pregnant mare's serum gonadotropin-primed immature
rats, LH-beta. FSH-beta and alpha-subunit mRNA levels were significant
ly elevated at 1800 and 2000 h, paralleling the serum LH and FSH surge
. The progesterone antagonist RU486 (0.2 and 1.0 mg) significantly red
uced serum LH and FSH levels at 2000 h. The lower dose reduced LH-beta
and alpha-subunit mRNA levels at 2000 h and FSH-beta mRNA levels at 1
800 h. The higher dose caused an increase in LH-beta mRNA levels at 12
00 and 1800 h and a decrease in FSH-beta mRNA levels at 1800 and 2000
h. In conclusion, the present study provides evidence that preovulator
y progesterone plays an important role in the increase in FSH-beta mRN
A levels as well as the release of LH and FSH during the normal preovu
latory gonadotropin surge. This relationship appears to be dependent o
n the ongoing rate of synthesis because this does not occur in the ova
riectomized estrogen-primed rat in which synthesis is at a high basal
level. Furthermore, the correlation with FSH appears to be tighter as
compared to LH.