INVOLVEMENT OF ESTROGEN AND FOLLICLE-STIMULATING-HORMONE ON BASAL ANDLUTEINIZING-HORMONE (LH)-RELEASING HORMONE-STIMULATED LH-SECRETION INRU-486-INDUCED 3-DAY ESTROUS-CYCLE IN THE RAT
M. Tebar et al., INVOLVEMENT OF ESTROGEN AND FOLLICLE-STIMULATING-HORMONE ON BASAL ANDLUTEINIZING-HORMONE (LH)-RELEASING HORMONE-STIMULATED LH-SECRETION INRU-486-INDUCED 3-DAY ESTROUS-CYCLE IN THE RAT, Biology of reproduction, 58(2), 1998, pp. 615-619
Administration of 4 mg of the antiprogestogen RU-486 on proestrus (Day
1) to 4-day-cyclic rats advances the pituitary desensitization to neg
ative estrogen feedback and enhances pituitary responsiveness to LHRH.
These effects of RU-486 lead to a 1-day estrous cycle shortening. Mor
eover, administration of RU-486 in this study increased serum estradio
l-17 beta and decreased FSH concentrations during diestrus (experiment
1). The aim of the study was to examine the contribution of the exces
s of estrogen and the deficiency of FSH during diestrus to the 1-day e
strous cycle-shortening effect of RU-486 when injected on Day 1 in 4-d
ay-cyclic rats. The aim of the second and third experiments was to eva
luate the effects of 3 mg/0.2 ml oil of the antiestrogen LY117018-HCl
(LY) at 1800 h on Days 2 and 3, or 10 IU/0.2 ml saline of a recombinan
t human FSH (rhFSH) at 1700 h on Day 3 and at 0900 h on Day 4, with or
without 100 ng/0.5 ml saline of LHRH at 1200 h on Day 4, on uterine w
eight and serum concentrations of LH and estradiol-17 beta at 1300 h o
n Day 4 in rats given oil or RU-486 on Day 1 or 2. The aim of the four
th experiment was to evaluate the effect of combined LY and rhFSH trea
tments on uterine weight and serum levels of LH and estradiol-17 beta
in rats injected with RU-486 on Day 1. Administration of RU-486 on Day
1 significantly increased serum estradiol-17 beta on Days 3 and 4, wh
ereas administration on Day 2 slightly increased serum estradiol-17 be
ta on Day 4 only. Injection of RU-486 on either Day 1 or 2 decreased F
SH serum concentrations on Days 3 and 4 to a similar extent. Treatment
with LY reduced both basal and LHRH-stimulated LH secretion only in r
ats injected with RU-486 on Day 1, while rhFSH treatment attenuated ba
sal and stimulated LH secretion regardless of treatment. Treatment wit
h LY and rhFSH combined completely reversed the effects of RU-486 on D
ay 1 on LH serum concentrations. These data suggest that both the incr
eased estradiol-17 beta and the decreased FSH serum concentrations dur
ing diestrus in rats given RU-486 on proestrus are involved in the cha
nges of pituitary function leading to a 1-day estrous cycle shortening
.