Developmental, stage-specific, and hormonally regulated expression of growth hormone secretagogue receptor messenger RNA in rat testis

Recent evidence from our research suggested the 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 this paper, overall expression of GHS-R mRNA in rat testis was compared with 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 the 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 also showed 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 the 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.