Melatonin and human reproduction: Shedding light on the darkness hormone (original) (raw)

An Overview of Effects on Reproductive Physiology of Melatonin

Melatonin - Recent Updates [Working Title]

Melatonin is a neurotransmitter released from the pineal gland. The presence of receptor sites in the hypothalamus, pituitary gland, ovaries, and testicles and secretion of pituitary hormones (FSH and LH) are some of the effects of this hormone on reproduction. In addition to its systemic effect, it also showed an effect on ovarian physiology with the detection of high levels in the follicular fluid and the presence of melatonin receptors in the ovarian cells. In addition, it has been determined that melatonin affects follicular growth, oocyte maturation, ovulation, and luteal function. It has been stated that the effects of melatonin on the male reproductive system are indirectly effective through the gonads and indirectly by affecting the hormones. Again, some studies have expressed that melatonin has strong antioxidant properties and affects reproductive physiology due to this effect. This section discusses the effect of melatonin on male and female reproductive physiology.

Melatonin and Female Reproduction: An Expanding Universe

Frontiers in Endocrinology

For more than a half century the hormone melatonin has been associated with vertebrate reproduction, particularly in the context of seasonal breeding. This association is due in large measure to the fact that melatonin secretion from the pineal gland into the peripheral circulation is a nocturnal event whose duration is reflective of night length, which of course becomes progressively longer during winter months and correspondingly shorter during the summer months. The nocturnal plasma melatonin signal is conserved in essentially all vertebrates and is accessed not just for reproductive rhythms, but for seasonal cycles of metabolic activities, immune functions, and behavioral expression. A vast literature on melatonin and vertebrate biology has accrued over the past 60 years since melatonin's discovery, including the broad topic of animal reproduction, which is far beyond the scope of this human-focused review. Although modern humans in the industrialized world appear in general to have little remaining reproductive seasonality, the relationships between melatonin and human reproduction continue to attract widespread scientific attention. The purpose of this chapter is to draw attention to some newer developments in the field, especially those with relevance to human fertility and reproductive medicine. As the vast majority of studies have focused on the female reproductive system, a discussion of the potential impact of melatonin on human male fertility will be left for others.

Melatonin in male and female fertility

AL-Kindy College Medical Journal

Melatonin, a hormone synthesized mainly by the pineal gland, has been found in extra-pineal organs as well. It’s known as an organizer of circadian rhythms and more recently as an anti-oxidant. In addition to its role in maintaining immunity, pathophysiology of cardiovascular and neurological diseases, and as an anti-cancer agent, evidence has demonstrated that melatonin exerts a positive impact on male and female fertility primarily through oxygen scavenging effects. In In Vitro Fertilization (IVF) programs, supplementation of melatonin may be associated with better outcomes in terms of sperm quality, oocyte quality, embryo quality and pregnancy rates. This review summarizes various actions of melatonin on the body focusing on male and female fecundity.

Melatonin and Reproduction Revisited

Biology of Reproduction, 2009

This brief review summarizes new findings related to the reported beneficial effects of melatonin on reproductive physiology beyond its now well-known role in determining the sexual status in both long-day and short-day seasonally breeding mammals. Of particular note are those reproductive processes that have been shown to benefit from the ability of melatonin to function in the reduction of oxidative stress. In the few species that have been tested, brightly colored secondary sexual characteristics that serve as a sexual attractant reportedly are enhanced by melatonin administration. This is of potential importance inasmuch as the brightness of ornamental pigmentation is also associated with animals that are of the highest genetic quality. Free radical damage is commonplace during pregnancy and has negative effects on the mother, placenta, and fetus. Because of its ability to readily pass through the placenta, melatonin easily protects the fetus from oxidative damage, as well as the maternal tissues and placenta. Examples of conditions in which oxidative and nitrosative stress can be extensive during pregnancy include preeclampsia and damage resulting from anoxia or hypoxia that is followed by reflow of oxygenated blood into the tissue. Given the uncommonly low toxicity of melatonin, clinical trials are warranted to document the protection by melatonin against pathophysiological states of the reproductive system in which free radical damage is known to occur. Finally, the beneficial effects of melatonin in improving the outcomes of in vitro fertilization and embryo transfer should be further tested and exploited. The information in this article has applicability to human and veterinary medicine.

Melatonin and Sex Hormone Interrelationships - A Review

Journal of Pediatric Endocrinology and Metabolism, 1999

Melatonin, the main hormone secreted by the pineal gland at night, plays a major role in regulating reproductive physiology in seasonal breeders and influences the age of sexual maturation in laboratory rodents. In humans these relationships are less clear. Evidence supporting a melatonin-reproductive hormone relationship relies on findings of abnormal melatonin secretion in disorders of the reproductive system and on pathologies of the pineal gland which are associated with clinical abnormalities of the reproductive hormones. Normal melatonin rhythms are closely related to those of the reproductive hormones during infancy and reciprocally correlated during puberty. The demonstration of melatonin receptors in the brain and in reproductive organs, together with the localization of sex hormone receptors in the pineal gland, further strengthen these relationships. However, it is not yet clear that these correlations are functionally related, as data on the antigonadal effects of exogenous melatonin on the reproductive hormones are not conclusively established.

Short Review of Reproductive Physiology of Melatonin

2009

Epiphysis Cerebri also known as the Pineal gland produces the hormone melatonin. In 1955 Lerner and Takahashi first developed a so-called bioassay for melatonin determination based on a qualification of frog skin blanching Now melatonin is considered a hormone (N-acetyl-5 methoxy tryptamine) produced especially at night in pineal gland. Its secretion is stimulated by dark and inhibited by light, which takes place in the pinealocytes, the cellular unit of the pineal gland. Tryptophan is converted to serotonin and finally converted to melatonin, which is an Indole. Melatonin is metabolized to 6-hydroxyl-mel in the liver and the main metabolite excreted is 6-sulphatoxy-mel and this excretion urinary component is helpful in assessing pineal gland function especially in children

Peripheral Reproductive Organ Health and Melatonin: Ready for Prime Time

International Journal of Molecular Sciences, 2013

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.

Modulation of human ovarian function by melatonin

Frontiers in Bioscience-Elite

Introduction 3. Regulation of pineal melatonin biosynthesis 4. Influence of rhythmicity of melatonin during onset of puberty 5. Modulation of ovarian function by melatonin 5.1. Distribution of melatonin receptors in the ovary 5.2. Modulation of follicular growth by melatonin 5.3. Influence of melatonin on ovarian steroidogenesis 5.4. Effect of melatonin on ovulation 5.5. Effect of melatonin in maintenance of oocyte quality 6. Modulation of luteal function by melatonin 7. Protective effect of melatonin in embryo culture 8. Effect of melatonin in success rate of IVF 9. Conclusion 10. Acknowledgments 11. References

Role of melatonin in male reproduction

Asian Pacific Journal of Reproduction, 2019

summarizes the updated data on the versatility of melatonin as an endogenous rhythm setter, as an antioxidant molecule and its possible physiological impacts in male reproductive functions.

Role of melatonin in male reproduction Male infertility

Asian Pacific Journal of Reproduction, 2019

Melatonin, conventionally accepted as a pineal gland secretion, is a neuromodulator whose physiological concentrations are regulated by circadian rhythms. Alteration in melatonin levels owing to circadian influences is a major regulator of reproductive functions in animal species that are seasonal breeders. Attributing to its antioxidant properties and capability to cross physiological barriers, such as the blood-brain barrier, the blood-testis barrier as well as having almost no toxicity, melatonin finds high relevance in amelioration of male fertility parameters. Melatonin may affect male reproductive functions by influencing the release of hypothalamic gonadotropin-releasing hormone and pituitary luteinizing hormone, which are among the key hormones in regulation of male reproduction. It may directly act on testicular cells to influence testicular functions. The property of melatonin most essential for testicular functions is its ability to scavenge free radicals, thereby preventing testicular oxidative damage. This article summarizes the updated data on the versatility of melatonin as an endogenous rhythm setter, as an antioxidant molecule and its possible physiological impacts in male reproductive functions