THE ROLE OF MELATONIN IN THE HUMAN FETUS (REVIEW)

Melatonin, an indole amine, primarily derived from the pineal gland is secreted during the hours of darkness. Melatonin acts as a hormonal t ransduction of photoperiod influencing the timing of seasonal and dail y (circadian) physiological rhythms. Maternal melatonin crosses the pl acenta and enters the fetal circulation providing photoperiodic inform ation to the fetus influencing the subsequent circadian and seasonal r hythms of the offspring. The function of melatonin in humans is more o bscure. However, melatonin has attained prominence as a treatment for disturbed circadian rhythms and sleep patterns which occur as a result of transmeridian travel, shift work or blindness. The biological cloc k, the hypothalamic suprachiasmatic nuclei (SCN), possesses melatonin receptors, in both the adult and fetal human. This concurs with the re ported influence of melatonin on human circadian rhythmicity and indic ates that this influence may begin in utero. Melatonin receptors are w idespread in the human fetus and occur in both central and peripheral tissue from early in fetal development. Thus, the influence of melaton in on the developing human fetus may not be limited to entraining circ adian rhythmicity. Considering the transplacental availability of mela tonin to the fetus the ingestion of melatonin by pregnant women may be inadvisable.