SERUM INHIBIN-B IN HEALTHY PUBERTAL AND ADOLESCENT BOYS - RELATION TOAGE, STAGE OF PUBERTY, AND FOLLICLE-STIMULATING-HORMONE, LUTEINIZING-HORMONE, TESTOSTERONE, AND ESTRADIOL LEVELS

Inhibin B levels were measured in serum from 400 healthy Danish prepub ertal, pubertal, and adolescent males, aged 6-20 yr, in a cross-sectio nal study using a recently developed immunoassay that is specific for inhibin B, the physiologically important inhibin form in men. In addit ion, serum levels of FSH, LH, testosterone, and estradiol levels were measured. Serum levels of inhibin B, FSH, LH, testosterone, and estrad iol all increased significantly between stages I and II of puberty. Fr om stage II of puberty the inhibin B level was relatively constant, wh ereas the FSH level continued to increase between stages II and III. F rom stage In of puberty the FSH level was also relatively constant, al though there was a nonsignificant trend of slightly decreased FSH leve ls at pubertal stage V compared to stage IV. The levels of serum LH, t estosterone, and estradiol increased progressively throughout puberty. In prepubertal boys younger than 9 yr, there were no correlation betw een inhibin B and the other three hormones. In prepubertal boys older than 9 yr, a significant positive correlation was observed between inh ibin B and FSH, LH, and testosterone. However, at this pubertal stage, each hormone correlated strongly with age, and when the effect of age was taken into account, only the partial correlation between inhibin B and LH/testosterone remained statistically significant. At stage II of puberty, the positive partial correlation between inhibin B and LH/ testosterone was still present. At stage III of puberty, an negative p artial correlation between inhibin B and FSH, LH, and estradiol was pr esent, whereas no correlation between inhibin B and testosterone could be observed from stage III onward. The negative correlation between i nhibin B and FSH persisted from stage III of puberty onward, whereas t he correlation between inhibin B and LH and between inhibin B and estr adiol was nonsignificant at stages IV and V of puberty. In conclusion, in boys, serum inhibin B levels increase early in puberty; by puberta l stage II the adult level of inhibin B has been reached. The correlat ion of inhibin B to FSH, LH, and testosterone changes during pubertal development. Early puberty is characterized by a positive correlation between inhibin B and LH/testosterone, but no correlation to FSH. Late puberty (from stage III) is characterized by a negative correlation b etween inhibin B and FSH (which is maintained in adult men), a diminis hing negative correlation between inhibin B and LH, and no correlation between inhibin B and testosterone, suggesting that developmental and maturational processes in the hypothalamic-pituitary-gonadal axis tak e place, leading to the establishment of the closed loop feedback regu lation system operating in adult men. The positive correlation between inhibin B and LH/testosterone at the time when serum inhibin B levels rise early in puberty suggests that Leydig cell factors may play an i mportant role in the maturation and stimulation of Sertoli cells in th e beginning of pubertal development.