Abnormal melatonin secretion in male patients with hypogonadism

Effect of dihydrotestosterone on melatonin secretion and the expression of melatonin receptors and apoptosis-related factors in sheep epididymides

Melatonin (MEL) is involved in homeostasis of the epididymis lumen environment. Dihydrotestosterone (DHT) partakes in the development of gonads and organs in male animals. However, whether MEL secretion, the expression of its receptors, MT1 and MT2, and sheep epididymal epithelial cell apoptosis is regulated by DHT remains unclear. In this study, we used immunohistochemical staining to detect the distribution patterns of DHT synthetases [5α-reductase (5α-red)] and its androgen receptor (AR) in sheep epididymides. 5α-red1, 5α-red2, and AR were positively expressed in sperm, epididymal epithelial cells, and the smooth muscle cells of the caput, corpus, and cauda regions of the epididymis. DHT concentration and the expression levels of 5α-red and AR in the caput, corpus, and cauda regions were measured by enzyme-linked immunosorbent assay, liquid chromatography-mass spectrometry, real-time quantitative polymerase chain reaction, and western blot analysis. DHT concentration in the caput was significantly higher than those in corpus and cauda, probably because of the high expression of 5α-red2 in the caput and secretion and transport of DHT by the testicles. DHT inhibited MEL secretion, the expression of its membrane receptors, and MEL synthetases in cultured sheep epididymal epithelial cells in vitro. In addition, the Bax/Bcl-2 ratio, ACT CASP3, and caspase-3 mRNA expression were also decreased. The decreasing effect was partially reversed after flutamide treatment. Therefore, DHT regulates sheep epididymal function by influencing MEL expression and apoptosis-related factors. This study provides basic data for further research on the reproductive physiology of male animals.

Radiofrequency radiation: A possible threat to male fertility

Radiofrequency exposure from man-made sources has increased drastically with the era of advanced technology. People could not escape from such RF radiations as they have become the essential part of our routine life such as Wi-Fi, microwave ovens, TV, mobile phones, etc. Although non-ionizing radiations are less damaging than ionizing radiations but its long term exposure effect cannot be avoided. For fertility to be affected, either there is an alteration in germ cell, or its nourishing environment, and RF affects both the parameters subsequently, leading to infertility. This review with the help of in vitro and in vivo studies shows that RF could change the morphology and physiology of germ cells with affected spermatogenesis, motility and reduced concentration of male gametes. RF also results in genetic and hormonal changes. In addition, the contribution of oxidative stress and protein kinase complex after RFR exposure is also summarized which could also be the possible mechanism for reduction in sperm parameters. Further, some preventative measures are described which could help in reverting the radiofrequency effects on germ cells.

Melatonin and the skeleton

Melatonin may affect bone metabolism through bone anabolic as well as antiresorptive effects. An age-related decrease in peak melatonin levels at nighttime is well documented, which may increase bone resorption and bone loss in the elderly. In vitro, melatonin reduces oxidative stress on bone cells by acting as an antioxidant. Furthermore, melatonin improves bone formation by promoting differentiation of human mesenchymal stem cell (hMSC) into the osteoblastic cell linage. Bone resorption is reduced by increased synthesis of osteoprogeterin (OPG), a decoy receptor that prevents receptor activator of NK-κB ligand (RANKL) in binding to its receptor. Moreover, melatonin is believed to reduce the synthesis of RANKL preventing further bone resorption. In ovariectomized as well as nonovariectomized rodents, melatonin has shown beneficial effects on bone as assessed by biochemical bone turnover markers, DXA, and μCT scans. Furthermore, in pinealectomized animals, bone mineral density (BMD) is significantly decreased compared to controls, supporting the importance of sufficient melatonin levels. In humans, dysfunction of the melatonin signaling pathway may be involved in idiopathic scoliosis, and the increased fracture risk in nighttime workers may be related to changes in the circadian rhythm of melatonin. In the so-far only randomized study on melatonin treatment, no effects were, however, found on bone turnover markers. In conclusion, melatonin may have beneficial effects on the skeleton, but more studies on humans are warranted in order to find out whether supplementation with melatonin at bedtime may preserve bone mass and improve bone biomechanical competence.

Melatonin effects on luteinizing hormone in postmenopausal women: a pilot clinical trial NCT00288262

BACKGROUND

In many mammals, the duration of the nocturnal melatonin elevation regulates seasonal changes in reproductive hormones such as luteinizing hormone (LH). Melatonin's effects on human reproductive endocrinology are uncertain. It is thought that the same hypothalamic pulse generator may both trigger the pulsatile release of GnRH and LH and also cause hot flashes. Thus, if melatonin suppressed this pulse generator in postmenopausal women, it might moderate hot flashes. This clinical trial tested the hypothesis that melatonin could suppress LH and relieve hot flashes.

METHODS

Twenty postmenopausal women troubled by hot flashes underwent one week of baseline observation followed by 4 weeks of a randomized controlled trial of melatonin or matched placebo. The three randomized treatments were melatonin 0.5 mg 2.5-3 hours before bedtime, melatonin 0.5 mg upon morning awakening, or placebo capsules. Twelve of the women were admitted to the GCRC at baseline and at the end of randomized treatment for 24-hour sampling of blood for LH. Morning urine samples were collected twice weekly to measure LH excretion. Subjective responses measured throughout baseline and treatment included sleep and hot flash logs, the CESD and QIDS depression self-ratings, and the SAFTEE physical symptom inventory.

RESULTS

Urinary LH tended to increase from baseline to the end of treatment. Contrasts among the 3 randomized groups were statistically marginal, but there was relative suppression combining the groups given melatonin as contrasted to the placebo group (p < 0.01 one-tailed, Mann-Whitney U = 14). Similar but not significant results were seen in blood LH. There were no significant contrasts among groups in hot flashes, sleep, depression, or side-effect measures and no significant adverse effects of any sort.

CONCLUSION

The data are consistent with the hypothesis that melatonin suppresses LH in postmenopausal women. An effect related to the duration of nocturnal melatonin elevation is suggested. Effects of melatonin on reproductive endocrinology should be studied further in younger women and in men. Larger studies of melatonin effects on postmenopausal symptoms would be worthwhile.

Neurohypophysial hormone and melatonin secretion over the natural and suppressed menstrual cycle in premenopausal women

OBJECTIVE

Vasopressin, oxytocin and melatonin have been reported to be influenced by ovarian steroids. The neurohypophysial hormones have also been shown to display a diurnal pattern of secretion in men. We therefore studied the diurnal pattern of neurohypophysial hormone and melatonin secretion in premenopausal women and in women on oral contraceptives.

DESIGN

Healthy normally cycling premenopausal women were studied over 24 hours during the midfollicular and midluteal phases of the menstrual cycle. Healthy premenopausal women on oral contraceptives were studied over 24 hours at similar times.

SUBJECTS

Eight healthy normally cycling women and 7 healthy premenopausal women on oral contraceptives.

MEASUREMENTS

Plasma vasopressin, oxytocin and melatonin were measured by radioimmunoassay.

RESULTS

Vasopressin concentrations and its nocturnal peak were highest in the follicular phase of the natural menstrual cycle and attenuated in the women on oral contraceptives. Oxytocin concentrations did not vary between the two phases of the menstrual cycle, but increased on oestrogen administration. Overall melatonin secretion was augmented in the women on oral contraceptives.

CONCLUSIONS

Vasopressin release and its nocturnal peak were greatest in the follicular phase of the menstrual cycle, while melatonin secretion was augmented in the women on oral contraception.

Seasonal variation of gonadotropins and gonadal steroids receptors in the human pineal gland

Recently abnormal melatonin secretion was demonstrated in hypogonadal male patients which was normalized during testosterone administration. These results suggested that both gonadal steroids and gonadotropins may modulate melatonin secretion, probably by activating specific receptors in the pineal gland. We used immunohistochemistry to localize luteinizing hormone, follicle stimulating hormone, estrogen and androgen receptors in human pineal glands. Tissues were obtained at autopsy from 53 adult males (aged 19-94 years) over a period of 1 year. Positive staining for the four types of receptors was evident in all 53 specimens examined. The percent of positively stained cells revealed a significant seasonal variation of gonadotropin receptors with higher values in the winter than in the summer. Day-night difference was evident only for follicle stimulating hormone-receptors during the summer and winter, with higher values at night. Androgen receptors and estrogen receptors were present in all specimens but did not reveal day-night or seasonal variations. These data demonstrate the presence of gonadotropin and gonadal steroid receptors in the human pineal gland. Gonadotropin receptors exhibited seasonal variation with higher values in the winter.

Melatonin: role in gating nocturnal rise in sleep propensity

The present article reviews the evidence that melatonin possesses sleep-inducing effects and that it gates the increase in nocturnal sleepiness. It is shown that, without exception, all the studies that have investigated daytime administrations of melatonin reported increased sleepiness, even at doses that do not increase plasma levels of melatonin beyond its physiological levels. By contrast, nighttime increase in sleepiness was achieved only after administration of high doses. Based on these findings and on the precise coupling between the endogenous nocturnal increase in melatonin secretion and the opening of the sleep gate, it is suggested that melatonin participates in the regulation of the sleep-wake cycle by inhibiting the central nervous system wakefulness generating system. This inhibition allows a smooth transition from wakefulness to sleep. Clinical findings on decreased levels of nocturnal melatonin in chronic insomniacs, and on the efficacy of exogenous melatonin in improving sleep in melatonin-deficient insomniacs, are congruent with this hypothesis.