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Submitted on September 13, 2007
Accepted on January 17, 2008
Dept. of Pediatrics, University of Parma, Dept. of Gynecology-Obstetrics and Neonatology, University of Parma, Parma, Italy
* To whom correspondence should be addressed. E-mail: lucia.ghizzoni{at}unipr.it.
Contex: Growing evidence indicates that ghrelin may participate in the regulation of different aspects of the reproductive function. The genes encoding for this peptide and its receptor are expressed in the human ovary, but their functional role is still unknown.
Objective: The aim of our study was to assess whether ghrelin has any effect on steroid synthesis by human granulosa-lutein cells, and identify the receptor isoform through which this potential effect is exerted.
Design, patients and methods: Thirty five women with spontaneous ovulatory cycles undergoing in vitro fertilization for infertility due to uni- or bilateral tubal impatency or male factor were studied. Granulosa- lutein cells obtained from follicular fluid were incubated with increasing amounts of human acylated ghrelin (10-11 to 10-7 mol/L) either alone or together with a 1:500 concentration of a specific anti-ghrelin receptor antibody (GHS-R1a). Culture media were tested for estradiol (E2) and progesterone (P4). The expression of GHS-R1a and GHS-R1b in human granulosa-lutein cells was also studied by Real Time Quantitative PCR.
Results: Estradiol and progesterone concentrations in the culture media were significantly reduced by ghrelin in a dose–dependent fashion. The maximal decrease in E2 (25%) and P4 (20%) media concentrations was obtained with the 10-7 and 10-8 mol/L ghrelin concentrations, respectively. The inhibitory effect of all ghrelin concentrations used was antagonized by the specific anti-ghrelin receptor-1a antibody added to the culture media and not by the specific anti-ghrelin receptor-1b antibody. Both 1a and 1b isoforms of the GHS-R were expressed in human granulosa-lutein cells, with the latter exceeding the former's expression (GHS-R1b/GHS-R1a ratio: 143.23 ± 28.15).
Conclusions: Ghrelin exerts an inhibitory effect on granulosa-lutein cells steroidogenesis by acting through its functional GHS-R1a receptor. This suggests that ghrelin may serve an autocrine-paracrine role in the control of gonadal function, and be part of a network of molecular signals responsible for the coordinated control of energy homeostasis and reproduction.
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