Effects of light on human melatonin production and the human circadian system

Towards an evidence-based integrative lighting score: a proposed multi-level approach

Background: Human circadian clocks are synchronized daily with the external light-dark cycle and entrained to the 24-hour day. There is increasing evidence that a lack of synchronization and circadian entrainment can lead to adverse health effects. Beyond vision, light plays a critical role in modulating many so-called non-visual functions, including sleep-wake cycles, alertness, mood and endocrine functions. To assess (and potentially optimize) the impact of light on non-visual functions, it is necessary to know the exact 'dose' (i.e. spectral irradiance and exposure duration at eye level) of 24-hour light exposures, but also to include metadata about the lighting environment, individual needs and resources.

Problem statement: To address this problem, a new assessment tool is needed that uses existing metrics to provide metadata and information about light quality and quantity from all sources. In this commentary, we discuss the need to develop an evidence-based integrative lighting score that is tailored to specific audiences and lighting environments. We will summarize the most compelling evidence from the literature and outline a future plan for developing such a lighting score using internationally accepted metrics, stakeholder and user feedback.

Conclusion: We propose a weighting system that combines light qualities with physiological and behavioral effects, and the use of mathematical modelling for an output score. Such a scoring system will facilitate a holistic assessment of a lighting environment, integrating all available light sources.

Chronobiological Study Designs

The chapter describes experimental designs for various chronobiological studies aimed at basic research and clinical trials, with an emphasis on circadian rhythms. In the first part, various methods of data collection, particularly longitudinal and transverse sampling and their relative merits, are discussed. Thereafter, specific methods and their constraints for monitoring marker rhythms are presented. Variables that are most effective in characterizing the endogenous pacemaker and those of clinical relevance are discussed. Besides melatonin and core body temperature rhythms, which are widely accepted as the gold standard for representing the circadian clock, rhythms of cortisol concentration, physical activity, sleep parameters and chronotypes are considered. The relevance of stable rhythms with appropriate internal and external phase relationships for health and wellbeing, as well as adverse effects of certain rhythm alterations are discussed. The last part describes two experimental designs that allow separating endogenous and exogenous components of biological rhythms, the constant routine and the forced desynchronization protocols.

Light on Shedding: A Review of Sex and Menstrual Cycle Differences in the Physiological Effects of Light in Humans

The human circadian system responds to light as low as 30 photopic lux. Furthermore, recent evidence shows that there are huge individual differences in light sensitivity, which may help to explain why some people are more susceptible to sleep and circadian disruption than others. The biological mechanisms underlying the differences in light sensitivity remain largely unknown. A key variable of interest in understanding these individual differences in light sensitivity is biological sex. It is possible that in humans, males and females differ in their sensitivity to light, but the evidence is inconclusive. This is in part due to the historic exclusion of women in biomedical research. Hormonal fluctuations across the menstrual cycle in women has often been cited as a confound by researchers. Attitudes, however, are changing with funding and publication agencies advocating for more inclusive research frameworks and mandating that women and minorities participate in scientific research studies. In this article, we distill the existing knowledge regarding the relationship between light and the menstrual cycle. There is some evidence of a relationship between light and the menstrual cycle, but the nature of this relationship seems dependent on the timing of the light source (sunlight, moonlight, and electric light at night). Light sensitivity may be influenced by biological sex and menstrual phase but there might not be any effect at all. To better understand the relationship between light, the circadian system, and the menstrual cycle, future research needs to be designed thoughtfully, conducted rigorously, and reported transparently.

Impact of Evening Light Exposures with Different Solid Angles on Circadian Melatonin Rhythms, Alertness, and Visual Comfort in an Automotive Setting

Future automotive interior lighting might have the potential to go beyond decorative purposes by influencing alertness, circadian physiology, and sleep. As the available space in the interior of an automobile for lighting applications is limited, understanding the impact of various luminous surface sizes on non-image-forming effects is fundamental in this field. In a laboratory study using a within-subject design, 18 participants were exposed to two bright light conditions with different solid angles and one dim light condition in a balanced, randomized order during the course of the evening. Our results demonstrate that both light conditions significantly increased subjective alertness and reduced salivary melatonin concentration but not cognitive performance compared to dim light. The solid angle of light exposure at constant corneal illuminance only affected visual comfort. While subjective alertness can be increased and melatonin can be attenuated with rather small luminaires, larger solid angles should be considered if visual comfort is a priority.

Insomnia: Behavioral Treatment in the Elderly

Sleep quality in elderly individuals is affected by increased mental and physical health issues associated with aging, but also a decrease in sleep drive and an advance of the circadian phase. These issues may, in part, be due to lifestyle changes in older adults, such as retirement and/or reduced social and physical activity, which can lead to spending more time in bed, resulting in chronic insomnia. Cognitive behavioral therapy for insomnia has been shown to be an effective treatment method for difficulty sleeping in elderly individuals and should be the first-line treatment due to its efficacy and safety profile.

Bright Light Therapy and Circadian Cycles in Institutionalized Elders

BACKGROUND

Bright light therapy has been found to be an efficient method to improve the main parameters of circadian rhythms. However, institutionalized elders may suffer reduced exposure to diurnal light, which may impair their circadian rhythms, cognitive performance, and general health status.

OBJECTIVES

To analyze the effects of 5 days of morning exposure for 90 min to bright light therapy (BLT) applied to institutionalized elderly subjects with mild/moderate cognitive impairment.

SUBJECTS

Thirty-seven institutionalized subjects of both sexes, aged 70-93 years.

METHODS

The study lasted three consecutive weeks. During the second week the subjects were submitted to BLT (7000-10,000 lux at eye level) on a daily basis. Cognition, attention, and sleep quality were evaluated at the beginning of the first and third week. Circadian variables were recorded continuously throughout the 3 weeks. Non-invasive holders and validated tests were used to analyze the variables studied.

RESULTS

After BLT we have found significant improvements in general cognitive capabilities, sleep quality and in the main parameters of the subject's circadian rhythms. The results show that merely 90 min of BLT for five days seems to achieve a significant improvement in a constellation of circadian, sleep, health, and cognitive factors.

CONCLUSION

Bright light therapy is an affordable, effective, fast-acting therapy for age-related disturbances, with many advantages over pharmacological alternatives. We hypothesize these effects were the result of activating the residual activity of their presumably weakened circadian system.

Assessment of Circadian Rhythms

Circadian rhythms are observed in most physiologic functions across a variety of species and are controlled by a master pacemaker in the brain called the suprachiasmatic nucleus. The complex nature of the circadian system and the impact of circadian disruption on sleep, health, and well-being support the need to assess internal circadian timing in the clinical setting. The ability to assess circadian rhythms and the degree of circadian disruption can help in categorizing subtypes or even new circadian rhythm disorders and aid in the clinical management of the these disorders.

Salivary melatonin onset in youth at familial risk for bipolar disorder

Melatonin secretion and polysomnography (PSG) were compared among a group of healthy adolescents who were at high familial risk for bipolar disorder (HR) and a second group at low familial risk (LR). Adolescent participants (n = 12) were a mean age 14 ± 2.3 years and included 8 females and 4 males. Saliva samples were collected under standardized condition light (red light) and following a 200 lux light exposure over two consecutive nights in a sleep laboratory. Red Light Melatonin onset (RLMO) was defined as saliva melatonin level exceeding the mean of the first 3 readings plus 2 standard deviations. Polysomnography was also completed during each night. HR youth, relative to LR, experienced a significantly earlier melatonin onset following 200 lux light exposure. Polysomnography revealed that LR youth, relative to HR, spent significantly more time in combined stages 3 and 4 (deep sleep) following red light exposure. Additionally, regardless of the group status (HR or LR), there was no significant difference in Red Light Melatonin Onset recorded at home or in the laboratory, implying its feasibility and reliability.

Use of Light Therapy by Office-Based Physicians

BACKGROUND

Light therapy (LT) is a non-pharmacological biological treatment that has been used in psychiatry since the 1980s. Previous research has investigated the usage of LT in hospitals. The aim of this study was to examine the pattern of use of LT by office-based physicians.

METHODS

A questionnaire was sent by mail to 400 randomly selected doctors in Austria. We made sure that the sample was equally representative of general practitioners (GPs) and psychiatrists, public health service doctors and private doctors, physicians in cities and in the country as well as male and female doctors. Non-responders were asked by phone and e-mail to answer the questionnaire. We achieved a response rate of 27.7%.

RESULTS

LT was generally recommended by 67.3% of all physicians (91.6% of the psychiatrists but only 46.6% of the GPs). The recommended location of treatment was patients' homes in 90%. Physicians were asked whether they considered LT to be an appropriate treatment for various disorders. There were affirmative answers from: 94.2% for seasonal affective disorder (SAD), 93.3% for sub-syndromal SAD, 60.6% for non-seasonal recurrent major depressive disorder, 35.6% for jet lag syndrome, 35.6% for chronobiological problems with shift work, 22.1% for insomnia, 13.5% for premenstrual dysphoric disorder, and 10.6% for behavioural problems with Alzheimer's disease.

CONCLUSIONS

Our results indicate that LT is regularly recommended by office-based physicians, especially psychiatrists. However, there is potential for greater application of LT in indications other than depressive disorder. The results found here are comparable to previous findings in psychiatric hospitals.

Peripheral reproductive organ health and melatonin: ready for prime time

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.

Melatonin concentration as a marker of the circadian phase in patients with obstructive sleep apnoea

OBJECTIVE

The effects of obstructive sleep apnoea (OSA) on the markers of glucose metabolism and other hormones are of interest, particularly since there is growing evidence that OSA may be a risk factor for disorders such as insulin resistance. However, interpreting these studies depends on the target hormone not having a diurnal rhythm and the circadian rhythm not being altered by the sleep fragmentation that occurs in OSA. Therefore, the aim of our study was to test the hypothesis that OSA displaces the circadian rhythm.

METHODS

We carried out a prospective, observational, controlled, parallel study in 22 OSA patients (mean [SD] age: 45.1 [8.8]years; apnoea/hypopnoea index (AHI): 37 [24] events/h) and 22 age matched healthy subjects (age: 47.9 [7.9]years; AHI: 3 [1] events/h). Saliva samples for the measurement of melatonin were collected from participants resting in dim light at 30 min intervals between 19:30 and 22:30 h. Dim light melatonin onset (DLMO), a marker of the circadian phase, was taken at the end of the 30 min interval in which the greatest rise in melatonin occurred.

RESULTS

The group median (interquartile range) DLMO did not differ in OSA patients compared to healthy subjects (OSA patients: 90 [60-150]min; healthy subjects: 135 [90-150]min, p=0.19).

CONCLUSION

The circadian phase is the same in OSA patients and healthy subjects using salivary melatonin concentration as a marker of the circadian phase.

Magnetic fields and seasonality of affective illness: Implications for therapy

Seasonal affective disorder is characterized by recurrent winter depression associated with hypersomnia, overeating, and carbohydrate craving. The severe form of winter depression affects about 5% of the general population and is believed to be caused by light deficiency. About 70%-80% of patients with winter depression experience attenuation of symptoms when exposed to bright light therapy. Hypotheses pertaining to the pathogenesis of winter depression implicate the effects of light on different characteristics of circadian rhythms. One of the environmental factors which may be implicated, in addition to light, in the pathophysiology of winter depression is the geomagnetic field. There is strong indication that the pineal gland is a magnetosensitive system and that changes in the ambient magnetic field alter melatonin secretion and synchronize the circadian rhythms. In man, shielding of the ambient magnetic field significantly desynchronizes circadian rhythms which could be gradually resynchronized after application of magnetic fields. The strength of the environmental magnetic field diminishes during the winter months, leading to increased susceptibility for desynchronization of circadian rhythms. Thus, since the acute application of magnetic fields in experimental animals resembles that of acute exposure to light with respect to melatonin secretion (i.e., suppression of melatonin secretion), magnetic treatment might be beneficial for patients with winter depression. In addition, since the environmental light and magnetic fields, which undergo diurnal and seasonal variations, influence the activity of the pineal gland, we propose that a synergistic effect of light and magnetic therapy in patients with winter depression would be more physiological and, therefore, superior to phototherapy alone.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of light on the human circadian pacemaker

The periodic light-dark cycle provides the primary signal by which the human circadian pacemaker is synchronized to the 24 h day. Earlier reports that social contacts were more effective than light in the entrainment of human circadian rhythms have not been supported by more recent studies. In fact, we have found that exposure to a cyclic light stimulus can induce strong (type 0) resetting of the human circadian pacemaker, indicating that exposure to light affects the pacemaker's amplitude of oscillation as well as its phase. These findings support Winfree's long-standing prediction, based on his pioneering recognition of the importance of amplitude in the analysis of circadian clocks, that strong (type 0) resetting would prove to be a common property of circadian resetting responses to light across a wide array of species, from algae to humans. Research on humans has shown, for the first time, that the response of the circadian pacemaker to light depends not only on the timing, intensity and duration of light exposure, but also on the number of consecutive daily light exposures. Exposure to light of a critical strength at a critical phase can even drive the human circadian pacemaker to its region of singularity, akin to temporarily 'stopping' the human circadian clock. These findings have important implications for the treatment of circadian rhythm sleep disorders, because properly timed exposure to light can reset the human clock to any desired hour within one to three days.

Serum melatonin and urinary 6-sulfatoxymelatonin in major depression

In this study, serum melatonin and urinary 6-sulfatoxymelatonin (aMT6s) were measured in 14 major depressive inpatients, compared to 14 matched controls according to age, gender, season and hormonal treatment in women. Moreover, the relationship between serum melatonin and urinary aMT6s levels was analysed in the two groups. Results indicated that the two groups of subjects showed a clear melatonin rhythm without significant difference in the mean level of melatonin or aMT6s, in the area under the curve of melatonin or in the melatonin peak. However, the time of the nocturnal melatonin peak secretion was significantly delayed in depressive subjects as compared to healthy controls. Moreover, the depressed patients showed urinary aMT6s concentrations enhanced in the morning compared to night time levels, while these concentrations were lowered from the night to the morning in the control group. These results suggest that the melatonin production is phase-shifted in major depression.

Nonsteroidal anti-inflammatory drugs alter body temperature and suppress melatonin in humans

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis in humans. Prostaglandins are involved in thermoregulation, melatonin synthesis, and sleep. To determine effects of NSAIDs on body temperature (BT) and melatonin synthesis (MT) in humans, and to elucidate mechanisms by which NSAIDs may alter sleep patterns, a series of experiments using the NSAIDs aspirin and ibuprofen was conducted. Seventy-five subjects were tested under several experimental protocols. BT after NSAID or placebo was assessed in both between- and within-subjects designs at night and during the day. MT levels were assessed after NSAID or placebo at night in a within-subjects design. The normal nocturnal BT decrease was attenuated and MT was suppressed after NSAID relative to after placebo administration. Lower MT levels were associated with a relative flattening of BT. Daytime BT was not affected by NSAIDs. These results are compatible with the hypothesis that some of the behavioral changes associated with NSAIDs, including changes in sleep, are due to changes in BT and MT. We speculate that NSAID effects on sleep and BT are related to prostaglandin synthesis inhibition and/or suppression of MT.

Light treatment for sleep disorders: consensus report. III. Alerting and activating effects

In addition to the well-established phase-shifting properties of timed exposure to bright light, some investigators have reported an acute alerting, or activating, effect of bright light exposure. To the extent that bright light interventions for sleep disturbance may cause subjective and/or central nervous system activation, such a property may adversely affect the efficacy of treatment. Data obtained from patient samples and from healthy subjects generally support the notion that exposure to bright light may be associated with enhanced subjective alertness, and there is limited evidence of objective changes (EEG, skin conductance levels) that are consistent with true physiological arousal. Such activation appears to be quite transient, and there is little evidence to suggest that bright light-induced activation interferes with subsequent sleep onset. Some depressed patients, however, have experienced insomnia and hypomanic activation following bright-light exposure.

Behavioural assessment of pinealectomy and foetal pineal gland transplantation in rats: Part II

Pineal gland is an endocrine organ which exerts regulatory effects on the activity of various organs and systems. The present study was undertaken to highlight in experimental animals the possible integrative function of this endocrine organ on a behavioural pattern. Pinealectomy and foetal pineal gland transplantation to a subpial cortical area close to the pinealectomized region was performed. Behaviour was defined through motor activity induced by low (2 mg/kg) and high (10 mg/kg) doses of amphetamine in rats. It was shown that pinealectomy produced significant different patterns of behaviour induced by low and high doses of amphetamine. In sham operated animals low dose amphetamine induced a significant locomotor stimulation but without stereotyped activity. High dose amphetamine induced stereotyped activity. After pinealectomy even low dose amphetamine produced the behavioural pattern of stereotyped activity resembling a high dose amphetamine-induced behaviour. This differential effect of amphetamine, seen in pinealectomized rats, was completely restored after transplantation. On the other hand, melatonin treatment did not generate a significant alteration of behavioural profile either in the control or pinealectomized group of rats. Results are discussed with regard to the general regulatory function of the pineal gland.

Circadian variations in the number of actively secreting sebaceous follicles and androgen circadian rhythms

Sebum excretion has been shown to demonstrate a circadian rhythm using a gravimetric method (cigarette paper). With the newly introduced method of Sebutape, we confirmed this periodicity and showed that the elevation in sebum excretion is correlated with an increase in the number of secreting follicles. We found, furthermore, that the number of secreting follicles on the forehead showed a distinct and statistically significant circadian rhythmicity, in contrast to those of the chest, which remained almost constant. The quantification in plasma levels of cortisol, melatonin, delta-4-androstenedione, dehydroepiandrosterone sulphate, and free testosterone showed no correlation with sebum excretion at either site. These observations suggest that local factors are involved in control of sebum secretion.

Alleviation of sleep maintenance insomnia with timed exposure to bright light

OBJECTIVE

Half of the population over 65 suffers from chronic sleep disturbance. As a consequence, almost 40% of hypnotic medications are prescribed to people over age 60. Yet, hypnotics are often of little benefit in this population. As such, an effective non-drug alternative could prove important in the management of age-related sleep maintenance insomnia. The current study sought to evaluate the efficacy of bright light exposure in the treatment of sleep maintenance insomnia.

DESIGN

Following baseline sleep and circadian rhythms assessment, subjects with sleep-maintenance insomnia were treated with timed exposure to either bright white light or dim red light for 12 consecutive days. Sleep and circadian rhythms recordings were subsequently obtained and measures of sleep quality were compared to assess efficacy of the treatments.

SETTING

Baseline and post-treatment sleep and circadian rhythms assessments took place in the Laboratory of Human Chronobiology, Department of Psychiatry, Cornell University Medical College. The treatment phase of the study was conducted in participants' homes.

PARTICIPANTS

Sixteen men and women between the ages of 62 and 81 years were studied. All subjects were free of hypnotic medication, and all had experienced sleep disturbance for at least 1 year prior to entering the study.

RESULTS

Exposure to bright light resulted in substantial changes in sleep quality. Waking time within sleep was reduced by an hour, and sleep efficiency improved from 77.5% to 90%, without altering time spent in bed. Increased sleep time was in the form of Stage 2 sleep, REM sleep, and slow wave sleep. The effects were remarkably consistent across subjects.

CONCLUSIONS

The findings demonstrate the effectiveness of timed exposure to bright light in the treatment of age-related sleep maintenance insomnia. With further refinement of treatment regimens, this non-drug intervention may prove useful in a large proportion of sleep disturbed elderly.

Tardive dyskinesia in bipolar disorders: possible role of pineal melatonin

Several clinical studies have suggested that patients with affective disorders, are at high risk for developing tardive dyskinesia (TD). An intriguing aspect of the relationship between TD and affective disorders involves mood dependent alterations in severity of TD. In most reported cases, depressive episodes are associated with exacerbation of TD, while manic episodes are accompanied by attenuation of TD. Current neurochemical hypotheses of TD do not explain adequately the relations of TD to depression or the mood dependent variations in the severity of TD. I propose that alterations in the secretory activity of pineal melatonin during manic and depressive episodes may explain better both the higher risk of TD in patients with affective disorders and the mood-dependent fluctuations in severity of TD. Consideration of pineal melatonin functions may further our understanding of the pathophysiology of TD in patients with affective disorders.

Mood-dependent fluctuations in the severity of tardive dyskinesia and psoriasis vulgaris in a patient with schizoaffective disorder: possible role of melatonin

There is evidence that patients with affective disorders are at high risk for developing Tardive dyskinesia (TD). In addition, in patients with bipolar illness, depressive episodes have been associated with exacerbation of the TD, while manic episodes were accompanied by attenuation of TD. Since depression is associated with diminished melatonin secretion, the high incidence of TD in patients with history of depression may be linked to diminished secretory activity of the pineal melatonin. We report a 28-year old female patient with schizoaffective disorder associated with psoriasis vulgaris in whom periodic exacerbation of depressive moods and suicidal thoughts were accompanied by worsening of the TD as well as the psoriatic lesions. Spontaneous improvements of mood were associated with disappearance of the involuntary movements and regression of the psoriatic lesions. Since melatonin secretion is diminished in patients with depression and in patients with psoriasis vulgaris, this report may add further support to the hypothesis that the development of TD may be associated with diminished secretory activity of pineal melatonin. The mechanisms by which diminished melatonin secretion may facilitate the emergence of TD are discussed. In addition, the possibility that light therapy, as has been successfully used in the management of seasonal affective disorders, may be useful in the management and perhaps prophylaxis of TD is discussed.

Mechanisms of action of ECT in Parkinson's disease: possible role of pineal melatonin

Recent clinical studies have suggested that electroconvulsive therapy (ECT) may be efficacious in the therapy of Parkinson's disease (PD). However, the mechanisms of action of ECT in PD are largely unknown. PD may be associated with reduction in the secretory activity of pineal melatonin, and the therapeutic efficacy of ECT in PD may be associated with an effect on the secretory activity of pineal melatonin. Further studies involving analysis of plasma melatonin levels and circadian release prior to and following ECT are needed more precisely to determine the role of pineal melatonin in PD and in the therapeutic efficacy of ETC in PD.

Bright light induction of strong (type 0) resetting of the human circadian pacemaker

The response of the human circadian pacemaker to light was measured in 45 resetting trials. Each trial consisted of an initial endogenous circadian phase assessment, a three-cycle stimulus which included 5 hours of bright light per cycle, and a final phase assessment. The stimulus induced strong (type 0) resetting, with responses highly dependent on the initial circadian phase of light exposure. The magnitude and direction of the phase shifts were modulated by the timing of exposure to ordinary room light, previously thought to be undetectable by the human pacemaker. The data indicate that the sensitivity of the human circadian pacemaker to light is far greater than previously recognized and have important implications for the therapeutic use of light in the management of disorders of circadian regulation.

A proposed mechanism for the visions of dream sleep

The visions of dream sleep are suggested to occur through a dream mechanism which implicates tryptamine derivatives as endogenous paychedelics. The hallucinations that occur in some schizophrenic syndromes are also proposed to occur through a similar, though desynchronized, mechanism. These compounds occur in the human pineal gland and are regarded as neurotransmitters or neuroregulators. A protocol for experimental verification is suggested.

Melatonin circadian rhythm in anorexia nervosa and obesity

The mean 24-hour secretion and circadian rhythm of melatonin were studied in 12 female subjects with anorexia nervosa (AN), 13 massively obese (OB) women, and 9 normal weight healthy volunteers to investigate the relationship between type of feeding behavior and hormonal secretory pattern. Blood samples for melatonin were drawn every 4 hours from 0400 h to 2400 h and every 2 hours from 2400 h to 0400 h. Mean 24-hour melatonin secretion was significantly higher in AN than in OB patients and controls. Melatonin circadian rhythms were disrupted in 8 of the 12 AN patients and in 9 of the 13 OB subjects, with phase-advanced nocturnal rises, abnormal diurnal peaks, or no nocturnal rises. The population mean cosinor analysis validated the existence of a significant circadian rhythm of the hormone in AN but not in OB subjects. No significant correlation between mean 24-hour secretion or type of circadian alterations and degree of weight deficit or excess was observed. The circadian alterations of melatonin in AN and OB may be linked to impaired secretory tonus of noradrenalin in the central nervous system, possibly unrelated to feeding patterns.

Melatonin and psychiatry

The pineal methoxyindole melatonin remains the most widely studied of the "pineal principles," and in subhuman species, the neuroendocrine status of this hormone is now generally acknowledged. In humans, however, no definitive functional activity for melatonin has yet been convincingly demonstrated, despite the description in recent years of marked changes in the metabolism of this hormone in several clinical categories. Currently, much interest is focused on the role that melatonin may play in various psychiatric disorders, and pineal research now represents one of the active areas of current psychiatry research. Investigators in this field have encountered many technical and practical difficulties, but the advent of the impressively sensitive and specific assay systems for melatonin has done much to facilitate the progress of research. Present ideas suggest a positive involvement of melatonin in affective disorders, possible involvement in the schizophrenic psychosis, and potential involvement of this hormone in other psychiatric categories. The present review discusses the etiological significance, diagnostic potential, and clinical utility of melatonin in psychiatry.

Pineal and circulating melatonin rhythms in the box turtle, Terrapene carolina triunguis: effect of photoperiod, light pulse, and environmental temperature

Pineal and circulating melatonin concentrations have been measured throughout the 24-hr cycle in the box turtle, Terrapene carolina triunguis, under different conditions of photoperiod and temperature. An obvious effect of photoperiod on the duration of the night rise of pineal and circulating melatonin is observed; the period of elevated melatonin is 4.30 hr in long photoperiod (18L:6D) and 11.00 hr in short photoperiod (8L:16D). A single pulse of 1 hr illumination beginning 1.30 hr after the onset of darkness, in a 16L:8D cycle, has no effect on pineal or circulating melatonin levels. A clear effect of environmental temperature on the amplitude of the day-night rhythm of melatonin production is observed. A possible role of the pineal of poikilotherms in the transduction of several environmental factors, via the daily pattern of melatonin secretion, is hypothesized.

5-Methoxypsoralen increases the plasma melatonin levels in humans

The aim of this study was to evaluate the acute effects of 5-methoxypsoralen (5-MOP) on the melatonin secretion in humans. Eleven normal volunteers were investigated before (drug-free) and after 6-day periods of treatment with oral 5-MOP, first administered daily at 9 A.M. and after a 1-week free interval administered daily at 9 P.M. Under nyctohemeral conditions, the plasma melatonin levels were evaluated over a 24-h period in each session by hourly blood samples and radioimmunoassay. The sensitivity of the retina to light was also evaluated by means of electroretinography performed at 11 A.M. before and after a morning administration of 5-MOP. Plasma levels of melatonin were significantly increased from the second hour after 5-MOP administration. The hourly mean levels were significantly higher after 5-MOP administration compared to baseline values. This increased secretion was more pronounced after evening than after morning administration. Also, 5-MOP increases the sensitivity of the retina to light under photopic conditions and in the early stages of the dark adaptation period, as observed under scotopic conditions.

Melatonin: perspectives in laboratory medicine and clinical research

We are presently at a point in human pineal research where we have recognized through melatonin assay the presence of pineal dysfunction in a variety of disease categories. Melatonin may now be quickly and accurately quantified in a range of body fluids, and our well-developed knowledge of the basic biochemistry and neuroanatomical connections of the pineal enables us to see at least how abnormalities in melatonin secretion occur, if not why. The reported increases in melatonin secretion in early malignancy with a reduction in secretion during the neoplastic process is interesting, as is the great decline in the elevated melatonin level of oncological patients following institution of chemotherapy. The correlations between estrogen receptor status of breast cancer and melatonin level, and between neoplastic status of the prostate and melatonin secretion, points to interesting differential diagnostic utilities of melatonin analysis in these conditions. Furthermore, an etiological involvement of melatonin in neoplasia is suggested by experiments which have demonstrated the capacity of melatonin to induce mitotic arrest, and to increase the affinity of mammary carcinoma estrogen receptors for their substrate. These are important observations among many others of direct relevance to research and treatment in oncology, and warrant much further investigation. Melatonin assay may also prove useful in the prognostic monitoring of patients treated for melatonin-secreting pineal tumors, and in such cases may form a logical part of follow-up investigation in the screening for metastatic complication. In psychiatry research, melatonin analysis has functioned as a tool by which alterations in pineal function within specific psychiatric diagnoses have been demonstrated and assessed. Its uses in the assessment of the effects of antidepressant drugs on central beta-receptor function, as a tool in the investigation of light-induced alterations in pineal function in manic-depressive individuals, and as a tool in the investigation of the putative pineal-adrenocortical functional interaction have produced the fundamental building blocks of modern research into the pineal and psychiatry. The experimental clinical utility of melatonin assay is not localized to oncology and psychiatry, and significant alterations in melatonin secretion have been reported in several other disease categories. Indeed, the demonstration of markedly elevated melatonin secretion in patients with spina bifida occulta might suggest that assay of melatonin in amniotic fluid could be useful as an experimental adjunct in the prenatal diagnosis of this condition.(ABSTRACT TRUNCATED AT 400 WORDS)

Circadian rhythms and their mechanisms

Recent work concerning the number, site(s) and means of adjustment to the 24-h day of internal clocks is reviewed. Work on humans is considered wherever possible though much of the work involving ablation and in vitro techniques necessarily involves other species, particularly rodents. It is concluded that, though recent advances have been impressive and present techniques appear likely to continue to produce results and stimulate discussion, more attention should be directed to considering the circadian system as a whole rather than as an assemblage of individual components.

The pineal gland: anatomy, physiology, and clinical significance

Since the discovery of melatonin approximately 25 years ago, there has been intense study regarding the details of the structure and function of the pineal gland. This work is reviewed, with particular emphasis on those aspects of importance to human physiology and disease.

Pineal melatonin rhythms in the lizard Anolis carolinensis: effects of light and temperature cycles

Pineal and ocular melatonin was assessed, over 24 h periods, in male lizards (Anolis carolinensis) entrained to 24 h light-dark (LD) cycles and a constant 32 degrees C, and in lizards entrained to both 24 h LD cycles and 24 h temperature cycles (32 degrees C/20 degrees C). At a constant temperature, the duration of the photoperiod has a profound effect on the duration, amplitude, and phase of the pineal melatonin rhythm (Fig. 1). The pineal melatonin rhythm under cyclic temperature peaks during the cool (20 degrees C) phase of the cycle regardless of whether or not the cool phase occurs during the light or dark phase of a LD 12:12 cycle (Fig. 3). Under a temperature cycle and constant dim illumination, a pineal melatonin rhythm is observed which peaks during the cool phase of the temperature cycle, but the amplitude of the rhythm is depressed relative to that observed under LD (Fig. 2). Illumination up to 2 h in duration does not suppress the nocturnal melatonin peak in the Anolis pineal (Fig. 4). No melatonin rhythm was observed in the eyes of Anolis under either 24 h LD cycles and a constant temperature (Fig. 1), or under simultaneous light and temperature cycles (Fig. 3). Ocular melatonin content was, in all cases, either very low or non-detectable.

The circadian rhythm in plasma melatonin concentration of the urbanized man: the effect of summer and winter time

Plasma melatonin rhythms were measured in healthy urbanized persons between July 4 and 5 and between January 13 and 14. In contrast to findings in other mammals studied thus far, no difference in the duration of elevated night melatonin concentration was observed between summer and winter. In winter, melatonin rhythms were phase-delayed by about 1.5 h as compared with summer patterns.

Existence and role of endogenous ocular melatonin

The proposed role of melatonin as an endogenously synthesized modulator of intraocular pressure in the eye was investigated. Melatonin levels were determined by radioimmunoassay in the iris, ciliary body and retina-choroid of pinealectomized or sham-operated chickens by day and by night. Pinealectomy had no effect on melatonin levels in the ciliary body or retina of chicken eyes; a diurnal rhythm continued to be observed in these tissues, with values higher by night than by day. Chloroform-extracted melatonin levels in the rabbit ciliary body showed a diurnal rhythm but melatonin levels in rabbit retina did not. Intracameral infusion of melatonin into cat eyes caused aqueous humor synthesis to decrease but caused a greater decrease in aqueous humor outflow facility, leading to a significant increase in intraocular pressure. The results suggest that melatonergic mechanisms in the eye could be responsible for the diurnal rhythm in IOP, and the synthesis and diurnal rhythm of this melatonin are independent of the pineal gland.