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Biomedical subjects

A J Lewy

Publications and source records attributed to A J Lewy.

At least 73 records · Page 4Linked to original sources
PubMed1986

Human melatonin production decreases with age.

The purpose of this study was to investigate the effects of time of year and demographic variables on the amplitude of melatonin production in normal human subjects. Melatonin production was estimated by measuring the overnight excretion of its major urinary metabolite, 6-hydroxymelatonin. Urine was collected on three consecutive nights in the summer from a sample of 60 normal subjects balanced for sex and age. The collections were repeated in a subgroup during the winter. Melatonin production clearly declined with age but was not influenced by other demographic variables or by season of the year.

Adult↗
PubMed1986

Clonidine reduces plasma melatonin levels.

Clonidine, an alpha-adrenoceptor agonist, reduces human plasma melatonin levels when administered intravenously at 2-3 micrograms kg-1 to sleeping volunteers. Measurement of plasma melatonin levels after administration of clonidine could be the basis for a clinical in-vivo test of alpha-adrenoceptors.

Adult↗
PubMed1986

The use of plasma melatonin levels and light in the assessment and treatment of chronobiologic sleep and mood disorders.

Using the highly accurate and sensitive gas chromatographic-negative chemical ionization mass spectrometric assay for plasma melatonin we have measured plasma melatonin in humans as a biological marker for 24-hour (circadian) and seasonal rhythms and the effects of light on these rhythms. We propose that there are at least three critical parameters for light to be chronobiologically active in humans: intensity, wavelength and timing. With regard to timing, we have found that bright light exposure in the morning advances circadian rhythms (shifts them to an earlier time) and bright light in the evening delays them (shifts them to a later time). We have suggested that chronobiologic sleep and mood disorders be "phase typed" into either the phase advance subtype or the phase delayed subtype and that these disorders can then be treated with either evening light (for phase advanced disorders) or morning light (for phase delayed disorders). Regarding the function of melatonin in humans, we have preliminary evidence that it may participate in the regulation of the circadian rhythm of intraocular pressure.

Biological Clocks↗
PubMed1986

The importance of melatonin and tumor markers in pineal tumors.

A series of cases are presented to illustrate various facets of the clinical management of pineal tumors. Emphasis is placed on markers of normal and neoplastic pineal function, and in particular melatonin. Although variable before therapy, after therapy four of five patients had little evidence of melatonin production, suggesting that pinealectomy had been complete.

Adolescent↗
PubMed1985

Melatonin, light and chronobiological disorders.

Human plasma melatonin concentrations can be measured accurately and sensitively by gas chromatography-negative chemical ionization mass spectrometry. With this assay, we have shown that: in rats and in humans, plasma melatonin is exclusively derived from the pineal gland; propranolol and clonidine reduce melatonin levels in human; some blind people appear to have free-running melatonin secretory circadian rhythms; bright light can acutely suppress human melatonin production according to a linear fluence-response relationship; manic-depressive patients appear to be supersensitive to light, even when they are well; melatonin levels are greater in manic patients than in depressed patients; in experiments to test the clock-gate model and the hypothesized phase-response curve, two different effects of light appear to present in humans: an acute suppressant effect (mainly in the evening during long photoperiods) and an entrainment effect (particularly during the morning but also in the evening). When blood is sampled for measuring melatonin levels as a marker for circadian phase position, bright light should be avoided after 5 p.m. (the dim light melatonin onset). Bright-light exposure in the morning appears to advance circadian rhythms, whereas bright-light exposure in the evening appears to delay them. Once a patient has been 'phase typed' (phase-advanced vs. phase-delayed), predictions can be made about whether morning or evening light would be more effective in treating the sleep or mood disorder.

Circadian Rhythm↗
PubMed1985

Lithium effects on selected circadian rhythms in rats.

Treating rats with lithium results in clear phase-delays in certain circadian rhythms but has no effect upon other rhythms. Phase-delays can be seen in running-wheel activity rhythms but under certain conditions, phase changes are not noted in SCN 2-DG uptake or pineal melatonin rhythms.

Animals↗
PubMed1985

Supersensitivity to light: possible trait marker for manic-depressive illness.

Exposure to light during the night reduces plasma melatonin levels. A previous study showed that, in response to light, nighttime plasma melatonin levels fell twice as much in a group of acutely ill manic-depressive patients as in a group of normal subjects. The present study compares 11 euthymic manic-depressive patients not taking medications with 24 age- and sex-matched normal subjects. Melatonin levels in these patients also fell twice as much as the levels of the normal subjects, suggesting that supersensitivity to light may be a trait marker for bipolar affective disorder.

Adult↗
PubMed1985

Surgical resection of a pineal tumor containing elements of germinoma and astrocytoma.

A 15-year-old boy presented with hydrocephalus due to a pineal tumor presumed to be a germinoma. After a shunting procedure, gross total tumor resection was carried out via an occipital transtentorial approach. Histopathological examination of the tissue demonstrated that, in addition to the expected germinoma, the tumor also contained areas of astrocytoma and areas that, taken in isolation as in a needle biopsy, could have been diagnosed as pineocytoma. The diagnosis and therapy of a pineal tumor of mixed histological types such as this lesion would be seriously compromised by "conventional" empiric radiation and even a stereotactic needle biopsy may not have provided an adequate tissue sample.

Adolescent↗
PubMed1984

Seasonal affective disorder. A description of the syndrome and preliminary findings with light therapy.

Seasonal affective disorder (SAD) is a syndrome characterized by recurrent depressions that occur annually at the same time each year. We describe 29 patients with SAD; most of them had a bipolar affective disorder, especially bipolar II, and their depressions were generally characterized by hypersomnia, overeating, and carbohydrate craving and seemed to respond to changes in climate and latitude. Sleep recordings in nine depressed patients confirmed the presence of hypersomnia and showed increased sleep latency and reduced slow-wave (delta) sleep. Preliminary studies in 11 patients suggest that extending the photoperiod with bright artificial light has an antidepressant effect.

Adult↗