Prepubertal increases in gonadotropin-releasing hormone mRNA, gonadotropin-releasing hormone precursor, and subsequent maturation of precursor processing in male rats.

Changes in gonadotropins and gonadal steroids during sexual maturation in rats and humans are well documented but little is known about hypothalamic gonadotropin-releasing hormone (GnRH) gene expression in relation to these events. This study measured hypothalamic proGnRH mRNA, GnRH precursor, and fully processed GnRH from postnatal day 8 until day 62 in male rats. GnRH precursor increased on day 22, reached a peak on day 24, declined on day 25 and returned to infantile levels by day 28. A secondary rise in precursor occurred at about day 40 when testosterone levels increased. GnRH mRNA increased on day 22 and remained elevated over the study period to day 26. GnRH increased on day 24 and remained at this level until a secondary rise occurred coincident with the testosterone rise at about day 40. The ratio of GnRH precursor to GnRH was high until day 24 and was low from day 26 onwards, reflecting a maturation of the processing enzyme system between these 2 d. Thus, an abrupt increase in GnRH gene transcription (mRNA) occurs early in juvenile male rats (day 22), well before the onset of puberty. An increase in GnRH precursor accompanies these early changes and this is followed by the maturation of processing as evidenced by the rapid decline of precursor and increase in GnRH from day 24 onward.