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Submitted on February 28, 2005
Accepted on May 10, 2005
Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel; Department of Chemistry and Bioscience, Chalmers University of Technology, Medicinargatan 7B, 405 30 Gothenburg, Sweden
* To whom correspondence should be addressed. E-mail: y.koch{at}weizmann.ac.il.
GnRH, the main regulator of reproduction, is produced in a variety of tissues outside of the hypothalamus, its main site of synthesis and release. We aimed to determine whether GnRH produced in the female rat pituitary and ovaries is involved in the processes leading to ovulation. We studied the expression patterns of GnRH and GnRH-R in the same animals throughout the estrous cycle, using Real-Time PCR. Hypothalamic levels of GnRH mRNA were highest at 17:00 h of proestrus, preceding the preovulatory LH surge. No significant changes in the level of hypothalamic GnRH-R mRNA were detected although fluctuations during the day of proestrus are evident. High pituitary GnRH mRNA was detected during the day of estrus, in the morning of diestrus-I, and at noon of proestrus. Pituitary GnRH-R displayed a similar pattern of expression, except on estrus, when its mRNA levels declined. Ovarian GnRH mRNA levels increased in the morning of diestrus-I and early afternoon of proestrus. Here too GnRH-R displayed a somewhat similar pattern of expression to that of its ligand.
To the best of our knowledge, this is the first demonstration of a GnRH expression pattern in the pituitary and ovary of any species. The different timing of the GnRH peaks in the three tissues implies differential tissue-specific regulation. We believe that the GnRH produced in the anterior pituitary and ovary could play a physiological role in the preparation of these organs for the mid-cycle gonadotropin surge and ovulation, respectively, possibly via local GnRH-gonadotropin axes.
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