LONGITUDINAL REPRODUCTIVE HORMONE PROFILES IN INFANTS - PEAK OF INHIBIN-B LEVELS IN INFANT BOYS EXCEEDS LEVELS IN ADULT MEN

The gonads are usually considered quiescent organs in infancy and chil dhood. However, during the first few postnatal months of life, levels of gonadotropins and sex hormones are elevated in humans. Recent epide miological evidence suggests that environmental factors operating peri natally may influence male reproductive health in adulthood. The early postnatal activity of the Sertoli cell, a testicular cell type that i s supposed to play a major role in sperm production in adulthood is la rgely unknown. Recently, the peptide hormone inhibin B was shown to be a marker of Sertoli cell function in the adult male. In the adult wom an, inhibin B is secreted by the granulosa cells. Longitudinal serum l evels of inhibin B were measured in healthy boys (n = 15) and girls (n = 15), in cord blood, and every third month during the first 2 yr of life. In addition, serum levels of FSH, LH, and testosterone (boys) we re measured in the same group of children. In boys, inhibin B, FSH, LH , and testosterone levels were all elevated at 3 months of age. Howeve r, the peak of inhibin B was unexpectedly high, into the supraadult ra nge (mean +/- SE, 378 +/- 23 pg/mL) and persisted much longer than the elevation of FSH, LH, and testosterone. Thus, although levels of FSH, LH, and testosterone decreased into the range observed later in child hood by the age of 6-9 months, serum inhibin B levels remained elevate d up to at least the age of 15 months. In girls, the hormonal pattern was generally more complex, with a high interindividual variation in l evels of inhibin B, FSH, and LK within each age. In conclusion, the su stained elevation of inhibin B to supraadult levels in infant boys ind icates that the neonatal period may be a developmental window importan t for Sertoli cell proliferation and maturation. Thus, the gonads may be potentially vulnerable to exogenous endocrine interference, e.g. fr om environmental factors during this period of life. Measurement of se rum levels of inhibin B in infants may give clinical clues about devel opmental deficiencies in the gonads that otherwise only become apparen t around puberty or later in life.