Abstract
Some environmental factors may influence the pituitary–gonadal function. Among these, light plays an important role in animals and in humans. The effect of light on the endocrine system is mediated by the pineal gland, through the modulation of melatonin secretion. In fact, melatonin secretion is stimulated by darkness and suppressed by light, thus its circadian rhythm peaks at night. Light plays a favorable action on the hypothalamic-pituitary axis likely inhibiting melatonin secretion, while the exogenous melatonin administration does not seem to impair the hormonal secretions of this axis. The basal and rhythmic pituitary–gonadal hormone secretions are regulated by a central clock gene and some independent clock genes in the peripheral tissues. Light is able to induce the expression of some of these genes, thus playing an important role in regulating the hormonal secretions of pituitary–gonadal axis and the sexual and reproductive function in animals and humans. The lack of light stimulus in blind subjects induces increase in plasma melatonin concentrations with a free-running rhythm of secretion, which impairs the hormonal secretions of pituitary–gonadal axis, causing disorders of reproductive processes in both sexes.
Highlights
Several endogenous and exogenous factors may influence endocrine secretions [1], including those of pituitary–gonadal axis [2]
Of particular importance are the projections of the suprachiasmatic nucleus (SCN) that reach the supraventricular zone and the hypothalamus because they provide, among other functions, the neuroendocrine regulation and the pineal melatonin secretion, which plays an intermediate role between the environment and the endocrine system
The authors who studied these patients concluded that some blind people can have a functional integrity of retino-hypothalamic tract (RHT), allowing a melatonin suppression when exposed to light stimulus and a sufficient sleep entrainment
Summary
Several endogenous and exogenous factors may influence endocrine secretions [1], including those of pituitary–gonadal axis [2]. Since light plays an important synchronizing role on the circadian rhythmicity, the alteration of photoperiod, or the lack of light stimulus, as occurring in blindness, may impair this rhythmicity [18].
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