Endocrine Abstracts

The hypothalamic-pituitary-gonadal (HPG) axis is a dynamic endocrine axis, with three main periods of activity - in foetal life, during mini-puberty, and then from puberty into adult reproductive life. Between these periods the axis is dormant and thus difficult to assess, especially in mid-childhood. Inhibin B and anti-Mullerian hormone (AMH) are both markers of gonadal function - of Sertoli cells of the testes and granulosa cells of the ovary - and are very useful investigative tools, both during periods of HPG axis activity and between times. Inhibin B and AMH are being increasing used in paediatric endocrinology to diagnose and measure response to treatment in infants and children with both primary and secondary hypogonadism. Ranges for both of these assays have been defined from birth to adolescence in both healthy and disease cohorts. Serum inhibin-B concentrations in males and females vary during childhood in response to gonadotropin secretion. In boys during the mini-puberty, when Sertoli cells proliferate but do not mature, serum inhibin-B concentrations increase to similar or higher concentrations to those observed in adolescent boys. These levels then decline to lower but readily measurable concentrations until they rise again early in puberty. Undetectable AMH and inhibin B are characteristic of congenital anorchia but may also be seen in males with severe hypogonadotropic hypogonadism. In healthy males, AMH is high in the foetus and newborn, peaking at mini-puberty around two months of age and then decreases by the age of one year. Patients with dysgenetic gonads have low serum AMH while values are elevated in tumours of the Sertoli or granulosa cells. A similar pattern in AMH concentrations during the first months of life has also been reported in infant girls, but the concentrations in girls are significantly lower. AMH plateaus during puberty as sign of androgen action. In girls, concentrations are a marker of ovarian granulosa cell function and are considered a novel marker for follicular reserve. This has importance, for example in Turner syndrome, for assessment of potential reproductive capacity.