Melatonin: data consistent with a role in controlling ovarian function

Melatonin: comprehensive profile

This chapter includes the aspects of melatonin. The drug is synthesized in the pineal gland starting from tryptophane or synthetically by using indole as starting material. Melatonin has been used as an adjunct to interleukin-2 therapy for malignant neoplasms, as contraceptive, in the management of various forms of insomnia, to alleviate jet lag following long flights, and finally as free radical scavenger and hence as an antioxidant and an anti-inflammatory. The chapter discusses the drug metabolism and pharmacokinetics and presents various method of analysis of this drug such as biological analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Night shift work and hormone levels in women

BACKGROUND

Night shift work may disrupt the normal nocturnal rise in melatonin, resulting in increased breast cancer risk, possibly through increased reproductive hormone levels. We investigated whether night shift work is associated with decreased levels of urinary 6-sulfatoxymelatonin, the primary metabolite of melatonin, and increased urinary reproductive hormone levels.

METHODS

Participants were 172 night shift and 151 day shift-working nurses, aged 20-49 years, with regular menstrual cycles. Urine samples were collected throughout work and sleep periods and assayed for 6-sulfatoxymelatonin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrone conjugate (E1C).

RESULTS

6-Sulfatoxymelatonin levels were 62% lower and FSH and LH were 62% and 58% higher, respectively, in night shift-working women during daytime sleep than in day shift-working women during nighttime sleep (P ≤ 0.0001). Nighttime sleep on off-nights was associated with 42% lower 6-sulfatoxymelatonin levels among the night shift workers, relative to the day shift workers (P < 0.0001); no significant differences in LH or FSH were observed. 6-Sulfatoxymelatonin levels during night work were approximately 69% lower and FSH and LH were 35% and 38% higher, compared with day shift workers during nighttime sleep. No differences in E1C levels between night and day shift workers were observed. Within night shift workers, 6-sulfatoxymelatonin levels were lower and reproductive hormone levels were higher during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.05).

CONCLUSIONS

These results indicate that night shift workers have substantially reduced 6-sulfatoxymelatonin levels during night work and daytime sleep and that levels remain low even when a night shift worker sleeps at night.

IMPACT

Shift work could be an important risk factor for many other cancers in addition to breast cancer.

Effect of antidepressants on melatonin metabolite in depressed patients

Antidepressants increase melatonin levels, but it is still unclear whether this effect is related to the improvement of depressive symptoms or to unrelated pharmacological action of antidepressants. To answer this question, the effect of antidepressants on 6-sulphatoxymelatonin (aMT6s), the main melatonin urinary metabolite, was examined in drug-free depressed patients - most of them antidepressant-naive. aMT6s was evaluated in 34 depressed patients, before and after 8 weeks of placebo (n = 12) or antidepressant (n = 22; fluoxetine, duloxetine or Hypericum perforatum). Both groups showed an improvement of depressive symptoms after treatment compared to baseline (Hamilton Depression scores): 17.0 +/- 1.4 vs. 9.0 +/- 2.8, P = 0.007 for placebo, and 18.6 +/- 1.1 vs. 11.8 +/- 1.6, P < 0.001 for antidepressants). After treatment, aMT6s levels increased after antidepressants (P < 0.01), but not after placebo (P > 0.05). As depressive symptoms improved both in patients taking antidepressant and in those taking placebo, but an effect of antidepressants could only be seen in those taking antidepressants, we suggest that melatonin changes after antidepressants are more likely due to a pharmacological action of these drugs on melatonin secretion.

Light exposure, melatonin secretion, and menstrual cycle parameters: an integrative review

Dysfunction in menstrual physiology has pronounced effects on quality of life, involving mood changes, body image, infertility, and pregnancy complications. Light exposure may affect menstrual cycles and symptoms through the influence of melatonin secretion. The purpose of this systematic review is to determine the current state of knowledge about the effects of light and melatonin secretion on menstrual phase and cycle alterations. A brief overview of the influence of melatonin on human physiology is included. There is evidence of a relationship between light exposure and melatonin secretion and irregular menstrual cycles, menstrual cycle symptoms, and disordered ovarian function. In women with a psychopathology such as bipolar disorder or an endocrinopathy such as polycystic ovary syndrome, there seems to be greater vulnerability to the influence of light-dark exposure. Research on the complex role of light-dark exposure in menstrual physiology has implications for treatment of menstrual-associated disorders.

Melatonin levels in drug-free patients with major depression from the southern hemisphere

The secretion of melatonin has been shown as abnormal in some depressed patients, but most such studies were conducted in the northern hemisphere and with severely depressed inpatients. The aim of this study was to evaluate melatonin excretion profiles in major depressive outpatients from São Paulo, Brazil, individually matched to well-screened healthy volunteers to examine whether melatonin abnormalities are also present in patients from the southern hemisphere, and in less severely ill patients. We analyzed 32 drug-free, depressed outpatients and 32 psychiatrically healthy volunteers matched for age and gender. We also examined a set of 15 drug-free depressed outpatients and 15 healthy volunteers that were matched not only for age and gender, but also for body mass index and season, all factors known to influence melatonin excretion in humans. All patients fulfilled DSM-IV criteria for major depression. We evaluated major urinary metabolite of melatonin, 6-sulphatoxymelatonin (aMT6s), produced over 24 h and divided into four periods (06:00-12:00, 12:00-08:00, 18:00-24:00 and 24:00-06:00 h). aMT6s measurements during the 24 and 6 h intervals were similar in the 32 depressed patients and 32 healthy volunteers matched for age and gender; further matching for body mass index and season did not alter the results. Our study supports others in which depressed patients were found to have similar melatonin levels than healthy volunteers. Melatonin excretion has been considered a physiological index for noradrenergic function, which in some studies were found to be altered than depressed patients. It is conceivable that the alteration of nocturnal melatonin in depressed patients occurs only in more severe depression.

Artificial Lighting in the Industrialized World: Circadian Disruption and Breast Cancer

Breast cancer risk is high in industrialized societies, and increases as developing countries become more Westernized. The reasons are poorly understood. One possibility is circadian disruption from aspects of modern life, in particular the increasing use of electric power to light the night, and provide a sun-free environment during the day inside buildings. Circadian disruption could lead to alterations in melatonin production and in changing the molecular time of the circadian clock in the suprachiasmatic nuclei (SCN). There is evidence in humans that the endogenous melatonin rhythm is stronger for persons in a bright-day environment than in a dim-day environment; and the light intensity necessary to suppress melatonin at night continues to decline as new experiments are done. Melatonin suppression can increase breast tumorigenesis in experimental animals, and altering the endogenous clock mechanism may have downstream effects on cell cycle regulatory genes pertinent to breast tissue development and susceptibility. Therefore, maintenance of a solar day-aligned circadian rhythm in endogenous melatonin and in clock gene expression by exposure to a bright day and a dark night, may be a worthy goal. However, exogenous administration of melatonin in an attempt to achieve this goal may have an untoward effect given that pharmacologic dosing with melatonin has been shown to phase shift humans depending on the time of day it's given. Exogenous melatonin may therefore contribute to circadian disruption rather than alleviate it.

Relationship between adenohypophyseal and steroid hormones and variations in serum and urinary melatonin levels during the ovarian cycle, perimenopause and menopause in healthy women

Morning levels of serum melatonin, FSH, LH, prolactin (PRL), progesterone and estradiol were studied by RIA during the ovarian cycle, perimenopause and menopause in 79 healthy women. FSH and LH levels showed a slight nonsignificant increase from the fertile period to perimenopause, exhibiting a significantly greater increase during menopause. PRL, progesterone and estradiol showed parallel changes, reaching lower levels during menopause. Serum melatonin levels decreased with age, attaining minimum levels in menopause. FSH and estradiol were significantly correlated with melatonin in the follicular phase, while in the luteal phase a negative correlation was found between melatonin, progesterone and estradiol. No significant correlations were noted between serum hormone levels during the perimenopausal period. In menopause, as during the follicular phase, melatonin and FSH were negatively correlated. As expected, a significant positive correlation was found between morning serum levels of melatonin and nocturnal urinary excretion of this indoleamine in all groups studied.

Melatonin secretion in Turner's syndrome: lack of effect of oestrogen administration

Melatonin secretion was investigated in 13 girls with Turner's syndrome before and after long-term oestrogen administration. Oestrogen treatment resulted in an increase in the serum levels of the hormone and a decrease in blood progesterone concentration. No change, however, was observed in the melatonin secretion pattern (in terms of peak values, time of peak level and total melatonin secretion) after oestrogen therapy. A distinct circadian rhythm in serum melatonin was evident in all subjects with peak occurring around 0200 h and concentration similar to those of normal subjects.