Abstract
Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.
Highlights
Melatonin (Figure 1) is a heterogeneously-acting molecule with an exceptionally large skill set
Based on what is described in this brief introduction, it is probable that no cell or function in either the plant or animal kingdoms totally escapes the impact of melatonin
18 patients undergoing in vitro fertilization-embryo transfer (IVF-ET) who had failed to become pregnant during a previous in vitro fertilization (IVF)-ET cycle were given either melatonin (3 mg daily) or vitamin E (600 mg daily) from the fifth day of the previous menstrual cycle to the time of oocyte/follicular fluid retrieval [96]
Summary
Melatonin (Figure 1) is a heterogeneously-acting molecule with an exceptionally large skill set. Based on what is described in this brief introduction, it is probable that no cell or function in either the plant or animal kingdoms totally escapes the impact of melatonin. Research especially within the last two decades has certainly borne this out, data that is available in numerous published reviews [52,53,54,55,56,57,58,59,60]. Summarized is only a miniscule amount of the extensive published data set. Topics selected for inclusion were those not recently covered in depth in other surveys. Emphasis is on the beneficial effects of melatonin, which seem to be the only actions this indoleamine has, on those organs/situations selected for inclusion in this review
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