Changes in serum inhibin B during normal male puberty

In adult men, inhibin B (InhB) regulates FSH secretion by a negative feedback. The aims of this study were to evaluate the changes of InhB during puberty in the male and the relationship between InhB and FSH, LH, testosterone and testicular volume.

Cross-sectional study.

InhB was measured using a two-site ELISA in 100 healthy boys subdivided by their pubertal development according to Tanner into five groups of 20.

During puberty we observed an increase of InhB level (G1 = 84.3 pg/ml, G3 = 132.2 pg/ml, G5 = 206.1 pg/ml). In G1, InhB correlated positively with FSH (P = 0.0001), LH (P = 0.005), testosterone (P = 0.001) and testicular volume (P = 0.007); in G5, InhB correlated inversely with FSH (P = 0.001) and LH (P = 0.045) and directly with testicular volume (P = 0.013). The multivariate analysis demonstrated that: in G1, FSH is the most important, and testosterone the second most significant, stimulus for InhB increase; in G2 only FSH has a positive effect on InhB variation; in G3 only mean testicular volume fits the model (G1-G3: InhB dependent variable); considering the FSH dependent variable, in G4, InhB is the most important stimulus for FSH decrease and mean testicular volume is a secondary directly proportional variable; in G5, only InhB shows a significant inverse relationship with FSH.

During puberty there is a regular increase of InhB. In the first phases of gonadal maturation, InhB and FSH correlate positively, while in mid-late stages the relationship is inverse. We found that in mid-puberty (G3-G4), the serum concentration of InhB increases, as its inverse relationship with FSH is being established and hence spermatogenesis.