Serum levels of INSL3, AMH, Inhibin B and Testosterone during pubertal transition in healthy boys

IntroductionInsulin-like factor 3 (INSL3) is a promising marker of Leydig cell function with potentially high clinical relevance. Limited data of INSL3 levels in relation to other reproductive hormones in healthy pubertal boys exist.AimTo evaluate longitudinal serum changes in INSL3 compared to luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, inhibin B, and anti-Müllerian hormone (AMH) during puberty in healthy boys.MethodsTen boys were included from the longitudinal part of the COPENHAGEN Puberty Study. Pubertal evaluation, including testicular volume, was performed and blood samples drawn every 6 months for 5 years. Serum concentrations of testosterone were determined by a newly developed LC-MS/MS method, and serum concentrations of INSL3, AMH, inhibin B, FSH and LH, respectively, were determined by validated immunoassays.ResultsSerum INSL3 levels increased progressively with increasing age, pubertal onset and testicular volume. In six of ten boys, LH increased prior to the first observed increase in INSL3. In the remaining four boys, the increase in LH and INSL3 was observed at the same examination. The increases in serum concentrations of LH, testosterone and INSL3 were not parallel or in ordered succession and varied inter-individuallyConclusionWe demonstrated that INSL3 concentrations were tightly associated with pubertal onset and increasing testicular volume. However, the pubertal increases in LH, INSL3, and testosterone concentrations were not entirely parallel, suggesting that INSL3 and testosterone may be regulated differently. Thus, we speculate that INSL3 provides additional information on Leydig cell differentiation and function during puberty compared with traditional markers of testicular function.