In order to investigate the mechanism underlying ovarian
steroid action on gene expression of hypothalamic
luteinizing hormone releasing hormone (
LHRH), changes in
LHRH mRNA level were determined by
RNA-blot hybridization assay. Twenty-eight-day-old female rats were ovariectomized (OVX) and implanted with
Silastic capsule containing either
17 beta-estradiol (E) or vehicle (V). Two days later (day 30), OVX + E-primed rats were given s.c.
progesterone (P, 1 mg) 6 h prior to
decapitation. Four experimental groups were studied: (1) intact, (2) OVX + V, (3) OVX + E, and (4) OVX + E + P-treated rats.
Poly(A) RNA fractions from hypothalami (40-50/group) were isolated, blotted onto
nitrocellulose paper and hybridized with 32P-end-labeled
LHRH oligonucleotides (29 mer) which are complementary to rat
LHRH mRNA. The hypothalamic
LHRH mRNA signal markedly attenuated 2 days following
ovariectomy. E replacement to OVX rats slightly increased
LHRH mRNA level, which is lower than that of the intact group. However, a single injection of P to OVX + E-treated rats notably augmented the
LHRH mRNA level over that observed in the intact group. In addition,
LHRH content and release in vitro were examined to correlate with changes in
LHRH gene expression.
Ovariectomy and the replacement of E and/or P resulted in a similar fashion of changes in
LHRH release and content as compared to alteration of
LHRH mRNA level. This study clearly demonstrates that P increases
LHRH mRNA level in the hypothalamus of OVX + E-primed immature rats.(ABSTRACT TRUNCATED AT 250 WORDS)