[Endocrine biochemistry of puberty].

Puberty corresponds to the development of gonads and secondary sexual characteristics, and on a biological point of view, to the functional maturation of the gonadal axis. Puberty begins at the age of 11.5 to 12 years in males and 10.5 to 11 years in females. Depending on secondary sexual characteristics, particularly pubic pilosity, puberty is classified in five stages (Tanner's stages). During puberty growth velocity increases in response to gonadal steroid secretion. From a biochemical point of view, three steps are involved in the development of the hypothalamo-hypophysogonadal axis: 1. nocturnal hypothalamic GnRH secretion increases and becomes pulsatile (a peak every 60 to 90 min); 2. the pituitary gonadotrophins FSH and LH follow the same pattern of secretion as GnRH; increase of GnRH and FSH/LH secretion is due to a decrease in hypothalamo-hypophysal sensitivity to the negative feed back exerted by circulating gonadal steroids; 3. secretion of estradiol in females and testosterone in males increases, as a consequence of pituitary stimulation. Hormonal exploration of puberty is mainly based on the measurement of FSH-LH and testosterone or estradiol. SDHA is also measured to investigate adrenal androgen secretion, which increases three or four years before puberty; this is related to the maturation of adrenal androgenic function (adrenarche). Dynamic tests are used to evaluate the biological stage of puberty (LH-RH test) and to measure the functional capacity of the testes. Pubertal abnormalities can theoretically be divided into precocious and delayed puberty. In the former, clinical and biological characteristics are used to define: dissociated puberties, central precocious puberty and peripheral precocious puberty. In the latter, hypogonadism has either a central origin (hypogonadotropic hypogonadism) or peripheral origin (hypergonadotropic hypogonadism).