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Original Studies |
Department of Reproductive Medicine, University of California-San Diego, La Jolla, California 92093-0633
Address all correspondence to: Dr. S. S. C. Yen, Department of Reproductive Medicine, University of California-San Diego, La Jolla, California 92093-0633. E-mail: dnye{at}ucsd.edu
Recently, we reported that the thecal compartment of the human ovary
contains a CRF system replete with gene expression and protein for
corticotropin-releasing factor (CRF), CRF-Receptor 1 (CRF-R1), and the
blood-derived high affinity CRF-binding protein (CRF-BP). Granulosa
cells are devoid of the CRF system. The parallel increases in intensity
of CRF, CRF-R1, and 17
-hydroxylase messenger ribonucleic acid (mRNA)
and proteins in thecal cells with follicular maturation suggest that
the intraovarian CRF system may play an autocrine role regulating
androgen biosynthesis, with a downstream effect on estrogen production
by granulosa cells. The functionality of the ovarian CRF system may be
conditioned by the relative presence of plasma-derived CRF-BP by virtue
of its localization of protein, but not transcript in thecal cells and
its ability to compete with CRF for the CRF receptor.
To further these findings, in the present study we have examined the
effect of CRF on LH-stimulated 17
-hydroxylase (P450c17) gene
expression and androgen production by isolated thecal cells from human
ovarian follicles (1113 mm). During the 48-h culture, addition of LH
(10 ng/mL) to the medium increased by 5- and 6-fold
dehydroepiandrosterone and androstenedione production by thecal cells.
Remarkably, the LH-stimulated, but not basal, androgen production was
inhibited by CRF in a time- and dose-dependent manner. The half-maximal
(ID50) effect dose of CRF occurred at 5 x
10-8 mol/L, and at a maximal concentration of
10-6 mol/L, CRF completely inhibited LH-stimulated
androgen production. This inhibitory effect of CRF became evident at
12 h (45%), and by 24 h the effect was more pronounced, with
a 70% reduction from baseline. As determined by Northern analyses, CRF
dose dependently decreased LH-stimulated P450c17 mRNA levels, with a
maximal inhibition of 85% P450c17 gene expression at a CRF
concentration of 10-6 mol/L. With the addition of
10-6 mol/L of the antagonist
-helical CRF-(941), the
inhibitory effect of CRF was partially reversed for both P450c17 mRNA
(75%) and androgen production (50%), indicating the CRF-R1-mediated
event.
In conclusion, the present study demonstrated a potent inhibitory effect of CRF on LH-stimulated dehydroepiandrosterone and androstenedione production that appears to be mediated through the reduction of P450c17 gene expression. Thus, the ovarian CRF system may function as autocrine regulators for androgen biosynthesis in the thecal cell compartment to maintain optimal substrate for estrogen biosynthesis by granulosa cells. Further studies to define the role of CRF-BP in the endocrine modulation of the intraovarian CRF system are needed.
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