Gonadotropin-releasing hormone receptor gene expression during pubertal development of female rats.

Appropriate expression of the GnRH receptor (GnRH-R) in gonadotrophs is critical for GnRH signaling and hence for gonadotropin secretion and sexual development. In the present work, we have studied the ontogeny of the steady-state GnRH-R mRNA levels in pituitaries of female rats from Day 5 to Day 55, when sexual maturity is attained. Developmental changes of gonadotropin subunit (alpha, FSHbeta, and LHbeta) mRNA levels were also assessed. In addition, the role of the endogenous GnRH on the maturational changes of GnRH-R and gonadotropin subunit gene expression was investigated. Messenger RNA levels were determined by Northern blot analysis of total RNA from anterior pituitaries. Amounts of the most abundant (5.0 kilobase [kb]) GnRH-R mRNA increased slowly from Day 5 through the infantile period, to peak at Day 20 ( approximately 4-fold increase vs. Day 5). Thereafter the levels of the GnRH-R mRNA decline abruptly by Day 25 (75% decrease vs. Day 20) and then fell slightly until Day 35. Parallel changes were observed on the 4.5-kb transcript of the GnRH-R gene. Alpha subunit mRNA was easily detected at Day 5 and its levels increased quickly through the beginning of the infantile period to peak at Day 10 (3.2-fold increase vs. Day 5); then it decreased by 85% at Day 35. FSHbeta and LHbeta mRNA levels rose slowly until Days 15-20, a short time before GnRH-R. Thereafter, the levels of both mRNAs fell until Day 35 (90% decrease vs. Day 15 for FSHbeta and 50% decrease vs. Day 20 for LHbeta). To ascertain whether developmental activation of the GnRH-R and gonadotropin subunit gene expression is GnRH dependent, we have studied the effect of blocking the endogenous GnRH action by treating developing female rats with the specific GnRH antagonist cetrorelix (1.5 mg/kg body weight/wk, s.c.) through the infantile (Days 5-20) and the juvenile period (Days 20-35). Cetrorelix completely blocked the rise of levels of the two most abundant species, 5.0 kb and 4.5 kb, of GnRH-R mRNA during the infantile phase and dropped them to almost undetectable levels during the juvenile prepubertal period. Cetrorelix also abolished the developmental rise of gonadotropin beta subunit mRNAs during the two periods of the study. In contrast, alpha subunit gene expression tended to decrease, but not significantly, with cetrorelix treatment during the two periods. These data demonstrate that sexual maturation of female rats is advanced by an early and strong induction of GnRH-R and gonadotropin subunit gene expression during the infantile period, followed by weaker persistent activation during puberty. Developmental GnRH-R and gonadotropin beta subunit gene expression is almost entirely GnRH dependent, not only in the juvenile prepubertal stage but also during the infantile period.

Gonadotropin-releasing hormone receptor gene expression during pubertal development of male rats.

Appropriate expression of the GnRH receptor (GnRH-R) in gonadotropes is critical for GnRH signaling and hence for gonadotropin secretion and sexual development. In the present work, we have studied the ontogeny of the steady-state GnRH-R mRNA levels in pituitaries of male rats from Day 5 to Day 55, when sexual maturity is attained. Developmental changes of gonadotropin subunit (alpha, FSHbeta, and LHbeta) mRNA levels were also assessed. In addition, the role of the endogenous GnRH on the maturational changes of GnRH-R and gonadotropin subunit gene expression was investigated. Messenger RNA levels were determined by Northern blot analysis of total RNA from anterior pituitaries. Amounts of the most abundant (5.0 kb) GnRH-R mRNA increased slowly from Day 5 through the infantile and the juvenile periods, to peak at Day 35 (12-fold increase vs. Day 5). Thereafter, the levels of the GnRH-R mRNA decline slightly until Day 55 (33% decrease vs. Day 35). Parallel changes were observed on the 4.5-kb transcript of the GnRH-R gene. Alpha subunit mRNA was easily detected at Day 5, and its levels increased progressively through the infantile period (2.5-fold increase) and peaked at Day 25 (3.3-fold increase vs. Day 5) with a smooth nonstatistically significant increment until Day 35; then it decreased by 41.5% at Day 55. FSHbeta and LHbeta mRNA levels rose slowly until Day 25. A sharp rise occurred thereafter to reach maximum levels at Day 35 (5.8-fold for FSHbeta and 3.8-fold for LHbeta vs. Day 25). Thereafter, the levels of both mRNAs fell until Day 55 (44.1% decrease for FSHbeta and 37.1% decrease for LHbeta vs. Day 35). To ascertain whether developmental activation of the GnRH-R and gonadotropin subunit gene expression is GnRH dependent, we have studied the effect of blocking the endogenous GnRH action by treating developing male rats with the specific GnRH antagonist cetrorelix (1.5 mg/kg body weight/week, s.c.) through the infantile (Days 5-20) and the juvenile periods (Days 20-35). Cetrorelix completely blocked the rise of levels of the two most abundant species, 5.0 kb and 4.5 kb, of the GnRH-R mRNA, during both the infantile and the juvenile periods. Cetrorelix also abolished the developmental rise of the gonadotropin beta subunit mRNAs during the two periods of the study. In contrast, the alpha subunit gene expression was not altered by cetrorelix treatment during any of the two periods. These data demonstrate that sexual maturation of male rats is accompanied by a progressive and concerted induction of GnRH-R and gonadotropin subunit gene expression. Developmental activation of GnRH-R and gonadotropin beta subunit genes is GnRH dependent. The apparent GnRH-independent regulation of the alpha-glycoprotein subunit mRNA levels may be due to the contribution of thyrotropes and perhaps to the presence of exclusive regulatory signals for this gene.