The role of the pineal body in the endocrine control of puberty

The pineal gland plays an important role in reproductive endocrinology. The epiphysis regulates seasonal variations in reproductive function of seasonally breeding animals. In humans, even if they are not seasonal breeders, the role of the pineal in reproductive endocrinology seems to be important as well. It appears to be of particular importance the endocrine control of the gland on pubertal sexual maturation. Even if not all researchers agree, several data suggest that elevated melatonin levels-characteristic of prepubertal age-keep the hypothalamic-pituitary-gonadal axis in quiescence: thus, an inhibitory effect on pubertal development is exerted. Subsequently, the decreasing serum melatonin with advancing age would result in activation of the hypothalamic pulsatile secretion of GnRH- and therefore of the reproductive axis-with consequent onset of pubertal phenomena. The production rate of melatonin does not change with age and no growth in pineal size from 1 to 15 years of age has been demonstrated by nuclear magnetic resonance (NMR) studies. Therefore the decrease of serum melatonin concentrations has been proposed to be due to the increase in body mass or, according to another hypothesis, to be also temporally linked to sexual maturation. Furthermore, recently, it has been suggested in rats that the pineal influences not only the pubertal sexual maturation, but even the gonadal and genital development and function of offspring, already during intrauterine life. Investigations are needed to evaluate this hypothesis in humans.