Urinary excretion of immunoreactive luteinizing hormone-releasing hormone-like material in children correlation with pubertal development

Sexual maturation of the hypothalamus: pathophysiological aspects and clinical implications

Sexual maturation in humans begins early in fetal life and culminates in adulthood when the gonads have acquired a full capacity for reproduction. It is remarkable that during this long process, the pituitary gonadal function, hence its hypothalamic control presents an alternative of activation and inhibition periods, during which the interrelations of the 3 components of the hypothalamic-pituitary-gonadal axis change gradually and inversely. The ontogeny of the hypothalamic-pituitary system, the varying activity of the reproductive endocrine system throughout sexual maturation and the developmental changes in the interrelations of the hypothalamic-pituitary-gonadal axis are reviewed: the most striking feature of human sexual development is the long inhibition of hypothalamo-pituitary function during childhood. Much indirect evidence points to the determining role of the CNS in the maturation of hypothalamic function: the occurrence of rhythms of secretion, the amplitude of secretions and peripubertal specific sleep-related nycthemeral rhythm of secretion at the onset of puberty. Despite the reality of a negative feedback control, these changes do occur independently of gonadal secretions since they are observed (qualitatively if not strictly quantitatively) in agonadal children. It is likely that neurotransmitters (dopamine, serotonine) and opiates have an inhibitory effect on Gn-RH release. But we still don't know their evolution during sexual maturation. It does not appear that melatonine plays any determinant role in the onset of human puberty. The clinical implications of our present understanding of the physiological events occurring during sexual maturation are several. Considering the major problems related to abnormal sexual maturation we will discuss successively: (1) diagnosis of hypogonadotrophic hypogonadism in early infancy; (2) differential diagnosis between premature thelarche and true sexual precocity; (3) the usefulness of endocrine investigations in the evaluation of hypothalamic-pituitary function; and (4) the new developments in the treatment of precocious puberty, delayed puberty or hypogonadism.

Pubertal development: normal, precocious and delayed

The present concepts on the neuroendocrine mechanisms which trigger pubertal development and modulate the progression towards sexual maturity have been reviewed. Essentially, puberty is presented as a continuum, the programming of which is initiated prenatally and which ends in adult life when all hormonal secretions become autoregulated. This continuum is dependent on a delicate equilibrium between CNS neurohormones (GnRH), neurotransmitters (biogenic amines), pituitary gonadotrophin (FSH, LH) secretion and the end-organ response (testis or ovary) through the activation of specific membrane receptors. The gonadal sex steroids (T, OE2) will activate specific cytoplasmic and nuclear receptors of target tissues and exert their biological action. Initially, the activity of the HPGA is manifested by nocturnal LH peaks, followed by increased gonadal secretion of T or OE2. Extremely sensitive to negative feedback by circulating androgen and/or oestrogen in prepuberty, an hypothalamic regulatory system called the gonadostat increases its threshold of sensitivity and eventually becomes autoregulated at a higher feedback level. Progressively, the hypothalamus becomes sensitive to positive feedback action of gonadal hormones, this phenomenon being important for the onset of ovulation. It is likely also that adrenal androgens play a permissive and supportive role in the onset and progression of pubertal development. Finally, full maturity is reached, with final adult height through fusion of the epiphysis, and fertility is achieved. The clinical manifestations of each developmental stage of puberty are described and abnormalities of sexual development reviewed. While over 90 per cent of cases of precocious pubertal development are idiopathic in girls, a space-occupying lesion in the hypothalamic-pituitary region is frequent in boys. Dissociated pubertal signs (premature adrenarche, pubarche, thelarche, menarche) are discussed, together with diagnosis and treatment of precocious puberty, whether it is idiopathic or occurring independently of the activation of the HPGA. In addition to delay of puberty on a constitutional basis, or related to chronic endocrine or non-endocrine diseases, the main clinical entities with gonadal insufficiency, primary (hypergonadotrophic) or secondary (hypogonadotrophic), are reviewed in boys and girls and their investigation and treatment discussed.