Hum. Reprod. Advance Access originally published online on October 28, 2004
Human Reproduction 2004 19(12):2748-2758; doi:10.1093/humrep/deh519
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GnRH agonist stimulation of the pituitarygonadal axis in children: age and sex differences in circulating inhibin-B and activin-A
1 Department of Pediatrics, Division of Endocrinology, University of Michigan, Ann Arbor, MI 48109-0646, 2 Department of Pediatrics, Division of Endocrinology, University of Chicago, Pritzker School of Medicine, Chicago, IL 60637-1470 USA and 3 Institute of Reproduction and Development, Monash University, Clayton, Victoria, 3168 Australia
4 To whom correspondence should be addressed at: D1205 MPB, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-0718, USA. Email: cmfoster{at}umich.edu
BACKGROUND: Inhibin-B decreases and activin increases FSH secretion in adults. We investigated whether an FSHinhibin/activin feedback loop exists before or during puberty. METHODS: FSH secretion was stimulated with 10 µg/kg leuprolide acetate (GnRH agonist) in 18 girls, ages 1.013.2 years, and 11 boys, ages 8.915.2 years, with variations in pubertal development, and in five normal 9- to 10-year-old girls. Blood, obtained at 0, 0.5, 1, 2, 4, 8, 12, 16, 20 and 24 h after GnRH agonist, was analysed for LH, FSH, activin-A, inhibin-A, inhibin-B, follistatin 288 and estradiol/testosterone. RESULTS: FSH increased within 30 min of GnRH agonist administration with a peak greater in girls than boys (P=0.0006). Baseline inhibin-B was greater in boys than girls (P=0.01), while baseline activin-A concentrations were greater in girls. GnRH agonist-stimulated FSH increased inhibin-B in girls by 8 h and in boys by 20 h (P<0.05), but did not affect activin-A. Inhibin-B increases were seen only in girls older than 5 years. CONCLUSIONS: An inhibin-BFSH feedback loop exists prior to the onset of puberty in girls older than 5 years. Sex differences in activin-A and inhibin-B concentrations may be responsible for sex differences in serum FSH concentrations.
Key words: FSH/gonadal peptides/inhibin/puberty