Role of inhibins in childhood and puberty

Inhibins, produced mainly in the gonads, suppress FSH synthesis. The bioact ive dimeric forms of inhibin (A and B) have been proposed as peripheral mar kers of Sertoli and granulosa cell function. The determination of serum dim eric inhibins from birth through adulthood reflects a distinct pattern of b oth inhibins in males and females. Concomitantly with the gonadotrophin sur ge, an important production of inhibin B is observed during the first month s of life. In males, inhibin B levels are higher than in females and persis t elevated up to childhood, whereas in females they decrease up to prepuber tal levels by 6 months of age. In girls, high serum levels of inhibin A are observed during the first two months of life; thereafter, they are undetec table until puberty. An active secretion of inhibin B persists in both male s and females in the period of maximal LHRH pulse generator restraint; howe ver, the possible gonadotrophin dependence of this production remains contr oversial. At puberty, a progressive rise in serum inhibin B occurs concomit antly with the increased production of sex steroids in both males and femal es. A similar secretion pattern of inhibin A is observed in girls. This inc rement is mainly exerted by gonadotrophins and modulated by multiple paracr ine/autocrine mechanisms within the ovary and the testis that regulate the dimerization of the inhibin subunits throughout pubertal maturation. The di fferences observed in males and females between circulating dimeric inhibin s in relation to gonadotrophins and sex steroid concentrations from birth t hrough puberty has opened a new perspective for research in human reproduct ion. These new markers may contribute to a better knowledge of the regulati on of the hypothalamic-pituitary-gonadal axis function and the physiopathol ogy of the mechanisms involved in sexual differentiation and/or fertility d isorders.