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Recent evidence from our group suggested a direct role of ghrelin in the control of testicular function. However, the pattern of expression and hormonal regulation of the gene encoding its cognate receptor, i.e. the growth hormone-secretagogue receptor (GHS-R), in the male gonad remains to be fully elucidated. In the present communication, overall expression of GHS-R mRNA in rat testis was compared to that of the functional receptor form, namely GHS-R type 1a, in different developmental and experimental settings. In addition, cellular distribution of GHS-R within adult testis tissue was assessed. Our analyses demonstrated persistent expression of GHS-R gene in rat testis throughout postnatal development. In contrast, testicular expression of GHS-R type 1a mRNA remained undetectable before puberty, and sharply increased thereafter. In adult testis, GHS-R1a mRNA expression presented a scattered pattern of cellular distribution, including Sertoli and Leydig cells that showed also specific GHS-R1a immunoreactivity. Expression of total GHS-R and specific GHS-R1a mRNAs was detected in isolated seminiferous tubule preparations, with varying levels throughout the defined stages of the spermatogenic cycle. In addition, testicular expression of total GHS-R and GHS-R1a mRNAs was up-regulated by exposure to ghrelin in vitro, and after stimulation with FSH in vivo. In conclusion, our data demonstrate that expression of GHS-R gene in rat testis takes place in a developmental, stage-specific and hormonally-regulated manner. Divergent expression of total GHS-R and type 1a specific mRNAs was detected at certain stages of postnatal development and spermatogenic cycle, thus raising the possibility that, in addition to net changes in GHS-R gene expression, the balance between receptor subtypes may represent a novel mechanism for the tuning of ghrelin sensitivity in rat testis.
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