Sexual dimorphism in the maturation of the pituitary-gonadal axis, assessed by GnRH agonist challenge

Abstract

Objective: To assess whether the maturational changes of the pituitary-gonadal axis in a healthy population show gender-specific changes and to establish normative data for the different Tanner stages. Design: Prospective, cross-sectional study. Methods: The GnRH agonist leuprolide acetate (500 μg) was administered s.c. to 60 boys and 81 girls (age range, 5-17 years). Serum steroids and gonadotropins were determined at 0 and 24 h and at 0, 3 and 24 h after GnRH agonist challenge respectively, whereas IGF-I, IGF-binding protein-1 (IGFBP-1), IGFBP-3 and sex hormone-binding globulin were measured at baseline. Results: Baseline and peak LH responses to the agonist in late puberty, and basal and peak FSH levels at all Tanner stages, were higher in girls than in boys. Girls showed higher IGF-I levels than boys throughout puberty, sharper decreases in IGFBP-1 and earlier and greater increases in 17-hydroxypregnenolone, dehydroepiandrosterone (DHEA) and DHEA-sulfate. Testosterone responses to the agonist increased during puberty in males, and showed no changes in females. Conversely, estradiol responses rose throughout puberty in females and remained unchanged until late puberty in males. Conclusion: Leuprolide acetate stimulates gonadotropin and gonadal steroid secretion during puberty in both sexes and increases FSH levels in prepubertal girls. Pubertal maturation of gonadotrope function is gender specific, as it appears to involve increases in both the releasable and reserve pools of LH in males, and of LH and FSH in females. The earlier increase in Δ5-steroids in girls may suggest a sharper rise in ovarian cytochrome P450c17 activity along the Δ5-steroid pathway, while the failure of estradiol to increase in response to leuprolide acetate in early pubertal males suggests a late maturation of aromatase activity.