Increase In Melatonin Content Research Articles

Development of a melatonin-based formulation for the treatment of insomnia in the elderly

Melatonin, a hormone produced by the pineal gland at night, influences circadian rhythms, most notably the sleep–wake cycle. Much scientific evidence indicates that melatonin has sleep-enhancing properties. Sleep after melatonin administration is more similar to that recorded during normally occurring sleep than after administration of currently available hypnotic agents. Impairment in melatonin production may contribute to the well-known increased incidence of insomnia in the aged. In addition, some medications may impair sleep by inhibiting or distorting the melatonin rhythm. Insomnia associated with diminished nocturnal melatonin secretion may benefit from melatonin replacement therapy. Melatonin is rapidly eliminated from the body. Hence, to maintain effective serum concentrations of melatonin throughout the night, a prolonged-release (PR) formulation of melatonin (Circadin™) has been developed which provides a melatonin profile that simulates the normal nocturnal increase in melatonin concentrations. The sleep-inducing effects of PR-melatonin, at a dosage strength of 2 mg, have been demonstrated in exploratory studies in elderly insomnia patients and patients with depression or schizophrenia and sleep complaints. In the USA melatonin is available without any medical indication as a nutritional supplement. Animal toxicological studies and clinical experience has not revealed any consistent pattern of adverse events or laboratory test value alterations associated with the administration of the PR-melatonin. Clinical trials in a large population of elderly insomniacs have been set up to provide the regulatory bodies with the required evidence on the safety and efficacy of PR-melatonin. Drug Dev. Res. 50:226–234, 2000. © 2000 Wiley-Liss, Inc.

Modulation of plasma melatonin concentrations by changes in posture.

Posture change from a lying position to a standing position results in a decrease in plasma volume, which leads to an increase in plasma constituents, especially that of proteins and blood constituents bound to them. The aim of the present study was to investigate the physiological effects of postural changes on plasma nocturnal melatonin concentrations in healthy human volunteers. The study was divided into four stages. During stage one, subjects were seated from 21.00 hr to 01.00 hr. In stage two, subjects were lying at ground level from 21.00 hr to 01.00 hr. In stage three, subjects were is a sitting position from 2100 hr to 2300 hr and then in a standing position from 23.00 hr to 24.00 hr, and back to the sitting position from 24.00 hr to 01.00 hr. In the final stage, subjects were in a lying position from 21.00 hr to 23.00 hr and then in a standing position from 23.00 hr to 24.00 hr and back to the lying position from 24.00 hr to 01.00 hr. AUC analysis showed significant differences between sitting and lying positions (t=2.84; P<0.05; df=5), with higher melatonin levels associated with the sitting position (mean difference in peak concentration of 17.1 pg/ml). Furthermore a change in posture from the lying to the standing position produced a statistically significant increase in melatonin concentrations (final stage) (t=-3.37; P<0.05; df=5) (mean difference in peak concentration of 28.5 pg/ml). No differences were found with a change in posture from a sitting to a standing position. The hemoconcentration and hemodilution associated with posture changes may play a role in altering plasma protein bound hormones such as melatonin.

Degeneration of Rat Retina is Paralleled by an Imbalance of the Redox Mechanism of Pteridines

Summary The RCS rat suffers from a genetic degeneration of retinal cell We have examined the pattern of oxidized and reduced monapterin and biopterin in retinas from RCS retinas and controls. The ratio of oxidized monapterin to reduced monapterin was significantly increased compared to controls. Since oxidized pterins have been shown to affect the enzyme (HIOMT) to successivly increase the content of melatonin, it can be suggested that destruction of visual cells by light exposure is based on an increase in melatonin content. Consequently, a lack of dihydro-d-monapterin reductase is postulated to be causative in the pathway for blinding in RCS rats.

Rapid-onset/offset, variably scheduled 60 Hz electric and magnetic field exposure reduces nocturnal serum melatonin concentration in nonhuman primates.

Experiments with rodents indicate that power-frequency electric field (EF) or magnetic field (MF) exposure can suppress the normal nocturnal increase in melatonin concentration in pineal gland and blood. In a separate set of three experiments conducted with nonhuman primates, we did not observe melatonin suppression as a result of 6 weeks of day-time exposure to combined 60 Hz electric and magnetic fields (E/MF) with regularly scheduled "slow" E/MF onsets/offsets. The study described here used a different exposure paradigm in which two baboons were exposed to E/MF with "rapid" E/MF onsets/offsets accompanied by EF transients not found with slowly ramped E/MF onset/offset; profound reductions in nocturnal serum melatonin concentration were observed in this experiment. If replicated in a more extensive experiment, the observation of melatonin suppression only in the presence of E/MF transients would suggest that very specific exposure parameters determine the effects of 60 Hz E/MF on melatonin.

Effect of MR imaging on the normal human pineal body: measurement of plasma melatonin levels.

Production of melatonin, a hormone synthesized and secreted by the pineal body, has been suppressed by electromagnetic fields in some but not all animal studies. Magnetic resonance (MR) imaging at 1.5 T was evaluated for its ability to modulate the level of melatonin in eight male volunteers. Subjects were exposed to three conditions, respectively, between 1:00 and 2:00 AM on different nights: (a) a series of routine MR pulse sequences for brain imaging in dark conditions, (b) dark control conditions, and (c) bright-light control conditions. Plasma was analyzed for melatonin and cortisol levels. Hormonal changes were analyzed by one-factor repeated measures within-subject analysis of variance. These conditions were associated with significant differences in melatonin levels: F(2, 6) = 7.95, and P = .021. Subjects exposed to darkness showed a typical increase in melatonin concentration. Subjects exposed to bright light showed a characteristic suppression of melatonin concentration. Those exposed to the MR imaging fields showed an increase in melatonin level similar to that seen in the dark control condition. Light and MR imaging had no significant effects on cortisol levels. Thus, MR imaging at field strengths known to modulate melatonin levels in rats did not suppress melatonin production in human subjects.

Effects of different lighting regimes on daily hormonal and behavioural rhythms in the pregnant ewe and sheep fetus.

1. We have studied the effect of altering the time of darkness during a 12 h photoperiod on the diurnal rhythms of maternal and fetal plasma melatonin and prolactin concentrations and fetal breathing movements (FBMs) in the late pregnant sheep. 2. Four ewes were exposed to a 'normal' 12 h light-12 h dark regime with lights off at 19.00 h. Eight ewes were exposed to an 'altered' 12 h light-12 h dark regime with lights off at 11.00 h. FBMs were recorded continuously and 2 hourly maternal and fetal blood samples taken during 24 h experiments between 120 and 138 days gestation. 3. Plasma melatonin concentrations were higher during the hours of darkness in the ewes and fetuses in both the normal and altered groups; i.e. altering the time of darkness was associated with a shift in the timing of the daily increase in melatonin concentrations in the mother and fetus. 4. In the fetuses, the mean 24 h plasma prolactin concentration was higher in the altered lighting group (28.8 +/- 6.1 micrograms/l) compared to the normal lighting group (13.0 +/- 3.9 micrograms/l). There was no difference, however, between groups in the daily variation of fetal plasma prolactin concentrations, which were higher at 17.00-01.00 h than at 05.00-19.00 h. Thus, altering the time of darkness did not change the timing of the daily plasma prolactin rhythm in the fetus. 5. Under the normal lighting regime maternal plasma prolactin concentrations were higher at 17.00-19.00 h (i.e. from 2 h before lights off) than at 09.00-11.00 h. In contrast, under altered lighting, plasma prolactin concentrations were higher at 01.00-07.00 h (i.e. 2-8 h after lights on) than at 09.00 h. 6. In the normal lighting group the incidence (min/h) of FBMs were highest at 16.00-21.00 h and reached a minimum at 05.00-06.00 h. In contrast, in the altered lighting group the incidence of FBMs was lowest at 19.00-20.00 h and reached a maximum at 11.00-12.00 h. 7. The results suggest that the light-dark cycle influences the diurnal modulation of FBMs, but not the daily variation of fetal plasma prolactin concentrations. The role of plasma melatonin concentrations, and evidence for a photo-inducible phase of increased prolactin secretion in the fetus, is discussed.

Circadian Variations in Plasma Melatonin, FSH, LH, and Prolactin and Testosterone Levels in Infertile Men

Circadian patterns of plasma melatonin, FSH, LH, prolactin, and testosterone were studied in 10 healthy men, 20 men with oligozoospermia, and 8 men with azoospermia. Circadian rhythms were found in concentrations of melatonin and prolactin, with higher values at night in comparison with daytime levels. In patients with oligozoospermia and azoospermia an elevation in melatonin levels was observed, and an increase in melatonin concentrations occurred before onset of darkness (i.e., at 2000 h). Levels of FSH, LH, and prolactin were elevated in infertile patients. The possibilities that an increase in melatonin concentrations is either the primary feature that leads to the regression of the seminiferous epithelium or is secondary and depends on elevated gonadotropins and/or prolactin levels are discussed.

Treatment with forskolin for 8 hours during the day increases melatonin synthesis in the Syrian hamster pineal gland in organ culture: The long lag period is required for RNA synthesis

The exposure of organ-cultured pineal glands of Syrian hamsters to forskolin, an adenylate cyclase activator, caused marked increases in melatonin levels when glands were collected in the second half of the dark period and incubated for 4 h. However, when glands were collected at the beginning of the dark period and incubated with the same drug, a significant increase in melatonin content was observed only after 6-8 h. Likewise, when glands were collected at the beginning of the light period, forskolin stimulated melatonin synthesis only after 6-8 h of incubation with the drug. These results support the existence of a relatively long lag period necessary for the induction of melatonin production in the Syrian hamster pineal gland. Experiments with actinomycin D indicate that RNA synthesis occurs during the lag period; thus, actinomycin D blocks the induction of melatonin synthesis by forskolin in glands collected at the beginning of the dark period and incubated for 8 h. In contrast, when pineal glands were collected from hamsters killed in the second half of the dark period, and incubated with forskolin for either 4 or 8 h, actinomycin D was unable to block the induction of melatonin production. These data suggest that RNA, presumably messenger RNA, which is necessary for increasing hamster pineal melatonin synthesis, is synthesized and accumulates during the first half of the night.

Neuroendocrine integrative mechanisms in mammalian pineal gland: Effects of steroid and adenohypophysial hormones on melatonin synthesis in vitro

The time course for the decrease in norepinephrine concentration of rat pineal explants in culture indicated a significant fall starting at the 4th hour and completed after 16–24 h of incubation. Significant decreases of serotonin and 5-hydroxyindoleacetic acid (HIAA) levels in tissue, an increase of HIAA/serotonin ratio, and an increase of melatonin production rate in vitro were also observed as a function of the incubation time. Estradiol (10 −7−10 −5 M) increased rat pineal melatonin content, testosterone (10 −5 M) decreased it and progesterone was devoid of activity when incubated with explants for up to 6 h. The in vitro stimulatory effect of estradiol on rat pineal methoxyindole synthesis was blocked by propranolol but not by phentolamine; propranolol also blocked the increase of nuclear estradiol-receptor complex produced by estrogen exposure of pineal explants. TSH (1–100 ng/ml), growth hormone (10–100 ng/ml) and LH (10 ng/ml) augmented rat pineal melatonin content while 100 ng/ml of FSH decreased it significantly. Prolactin exerted a biphasic effect on rat pineal explants, the lowest concentration augmenting melatonin content while the high concentration depressed it. Deep, intermediate and superficial segments of guinea-pig pineal glands showed an increase in melatonin concentration after a 6-h incubation in the presence of 10 −7−10 −5 M estradiol.

Episodic secretion of melatonin in pre- and postpubertal girls and boys.

The concentration of melatonin was determined in serum samples obtained at 15-min intervals during a 4-h period from seven normal girls, 9.5-16.5 yr of age, and eight normal boys, 9.0-16.8 yr of age. All samples were obtained between 0800 and 1300 h. An episodic pattern of melatonin secretion was found in all subjects. There was no significant (P greater than 0.1) difference between girls and boys as to number of episodes [3.1 +/- 0.4 (+/- SD) vs. 3.4 +/- 0.5 per 4 h), absolute melatonin increase (49.0 +/- 6.7 vs. 50.4 +/- 4.1 pg/ml), or apparent melatonin half-life (20.3 +/- 0.8 vs. 20.8 +/- 1.0 min). The mean absolute increase during secretory episodes correlated (r = 0.843; P less than 0.005) with the mean melatonin concentration per 4 h, and a significant (P less than 0.05) inverse correlation (r = -0.508) was found between the mean percent increment of the melatonin secretory episode and the mean apparent melatonin half-life. A significant correlation between melatonin secretion and previously reported (22) episodic LH secretion was not found. In girls and boys, the mean melatonin concentration increased with advancing puberty. The increase in melatonin concentration was due to an increase in the amplitude of secretory episodes. These data are consistent with an influence of gonadal function on melatonin secretion.

Regulation of rat pineal melatonin synthesis: Effect of monoamine oxidase inhibition

Inhibition of pineal monoamine oxidase (MAO) activity either by harmine or pargyline in adult male Sprague-Dawley rats housed in a 12 : 12 LD cycle resulted in increased pineal N-acetyltransferase (NAT) activity. Pineal MAO inhibition also increased pineal melatonin content, presumably as a result of the increased NAT activity. Conjunct treatment with propranolol, a β-adrenergic receptor antagonist, nullified these effects, regardless of the MAO inhibitor (harmine, pargyline or both) used or the inhibitor dose given. MAO inhibition during continuous light resulted in increased NAT activity greater than that observed following MAO inhibition during a 12 : 12 LD cycle. On the other hand, the increase in melatonin content following MAO inhibition during continuous light was not significantly different from that following MAO inhibition during a 12 : 12 LD cycle. Conjunct propranolol administration negated the effects of MAO inhibition on both the level of NAT activity and melatonin content, regardless of the lighting conditions. The level of pineal NAT activity is apparently regulated by the level of pineal β-adrenergic receptor stimulation. While melatonin production appears to be dependent on increases in NAT activity, biosynthesis of this methoxyindole may also be regulated, in part, by other factors or processes in the metabolic pathway.

Melatonin in the retina and the harderian gland. Ontogeny, diurnal variations and melatonin treatment

Using highly specific antibodies, melatonin has been identified immunohistologically in the rat retina, and the Harderian gland. The first truly significant amount of retinal melatonin was already detected in the 2 day old pups. The amount of melatonin progressively increased with age reaching adult levels around the 20th day. Diurnal variations with higher night levels of melatonin have been found in the adult in both retina and Harderian gland. Intraperitoneal injection or subcutaneous implantation of melatonin in beeswax (150 μg/rat) resulted in a vast increase in melatonin content in the retina and the Harderian gland of the juvenile and adult rats. No sexual differences have been registered in any experimental group. The concept of melatonin synthesis at peripheral sites independent of pineal production, the involvement of light-dark rhythm in the regulation of pineal and extrapineal melatonin content and the possibility of uptake mechanisms or receptors for melatonin in the retina and Harderian gland are discussed.

Increase in melatonin content of fetal sheep pineal tissue approaching term

Localization of the melatonin-synthesizing enzyme, hydroxyindole-O-methyltransferase (HIOMT)-like immunoreactivity was examined by light and electron microscopic immunocytochemistry, in the retinas of several species that have been used as animal models to study the retinal melatonin system. HIOMT-like immunoreactivity was observed in the retinal photoreceptors of rabbit, pigmented rat, guinea-pig, chick, goldfish, African clawed toad, and leopard frog. Additionally, most species displayed HIOMT immunoreactivity in a population of bipolar cells in the inner nuclear layer. At the ultrastructural level, HIOMT-like immunoreactivity was localized to the cytoplasm of rod and cone photoreceptors, and a population of cone bipolar cells. These observations are identical to earlier observations in the human retina. The similar pattern of HIOMT-like immunoreactivity among species suggests a phylogenetic conservation of the melatonin-synthesizing capability of retinal photoreceptors and some bipolar cells.

Control of pineal indole biosynthesis by changes in sympathetic tone caused by factors other than environmental lighting.

The melatonin (5-methoxy-N-acetylserotonin) content and N-acetyltransferase activity of rat pineal increase rapidly in response to physical immobilization or insulin-induced hypoglycemia. Carbohydrate consumption, which causes insulin release without hypoglycemia, does not elicit these pineal responses. Prior treatment with propranolol, a beta-adrenergic blocking agent, inhibits the N-acetyltransferase responses to hypoglycemia and immobilization, indicating that these changes result from stimulation of pineal beta-receptors by a catecholamine, presumably norepinephrine released from pineal sympathetic nerve terminals. Prior destruction of those terminals with 6-hydroxydopamine does not block, but actually potentiates, the increase in melatonin content and N-acetyltransferase activity after induced hypoglycemia or immobilization. This finding probably reflects an action of circulating catecholamines, secreted from the adrenal medullae or surviving sympathetic nerve terminals, on supersensitive pineal cells. These observations indicate that factors other than changes in environmental lighting, which modify sympathetic nervous tone, can also influence pineal function.