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G. E. Webley
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H. Mehl
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K. P. Willey
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ABSTRACT

The role of melatonin in animals which do not show marked seasonal changes in reproduction is disputed, in part because of the wide variation in reported concentrations. One reason for this may be the difficulties associated with the measurement of low molar concentrations of melatonin and the presence of a wide variety of potentially cross-reacting substances. The availability of a high affinity antiserum has allowed an assay, with low cross-reactivity and good sensitivity, to be established for the direct measurement of melatonin in a wide range of biological fluids, in particular serum, plasma and follicular fluid from man and rat. The high affinity of the antiserum enabled a tritium label of high specific activity to be used, removing the problems associated with the iodination of a small molecular weight compound. Melatonin concentrations in the assay were evaluated by four different methods: UV absorbance, gas chromatography, comparison of the immunoreactive concentrations of the label with the expected concentration by dilution and by comparison with a previously established assay which uses the same antiserum.

Melatonin was measured in serum from twelve healthy women over two 24-h periods; eight women with normal menstrual cycles and four taking the contraceptive pill. Concentrations were found to range from 19·8 to 215 pmol/l during the day in both groups. In women with normal menstrual cycles peak concentrations of 513·2 ± 54·1 (s.e.m.) pmol/l were recorded at 04.00 h, whereas higher concentrations were found in women taking the pill, reaching a peak of 849·12 ± 21·8 (s.e.m.) pmol/l at 04.00 h. Similar melatonin concentrations were measured in the two 24-h periods.

In the adult male rat, serum melatonin concentrations varied from 92·66 ± 37·9 (s.e.m.) pmol/l at 12.00 h, rising to 526 ± 55·6 (s.e.m.) pmol/l at 04.00 h.

This direct assay is more practical and robust than the assays currently available. The careful validation of assay characteristics allows its widespread use in both clinical studies and the investigation of the role of melatonin in different species.

J. Endocr. (1985) 106, 387–394

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A. Reinberg
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Y. Touitou
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A. Restoin
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C. Migraine
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F. Levi
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H. Montagner
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ABSTRACT

Circadian and ultradian rhythms in urinary excretion of 17-hydroxycorticosteroids were documented individually during an 8-day span in two pairs of young male twins. Studies were performed once at the age of 6 years for dizygotic twins and twice at the ages of 4·3 and 10·3 years for monozygotic twins. Four different methods were used for time-series analyses: chronograms (raw data), best-fitting curves resulting from cosinor analyses, power spectra and correlations of time-qualified data. Estimates of rhythm parameters (prominent periods, acrophases, etc.) as well as shapes of curves were closer in mono- than in dizygotic twins. Both similarities and small differences in rhythm characteristics of monozygotic twins were detected at both ages considered.

J. Endocr. (1985) 105, 247–253

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W. J. FULKERSON
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B. Y. TANG
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Three Merino ewes, adapted for about 3 weeks to their environment, were bled at 10 min intervals through a jugular venous cannula. Radioimmunoassay of plasma samples for cortisol revealed marked diurnal variations with peak levels just after midnight and lowest values in the afternoon. This rhythm appeared to result from a changing amplitude associated with a distinct ultradian rhythm (frequency 0·8–1·2 cycles/h) in the plasma level of cortisol. Calculation of the daily rate of secretion of cortisol from the hormone profiles gave a mean value of 8·49 mg. Arguments are put forward in favour of this method for obtaining the true rate of secretion of cortisol.

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Henrik Oster Institute of Neurobiology, University of Lübeck, Lübeck, Germany

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nocturnal light pollution and sleep-wake rhythm disruption in the case of the circadian clock. Ultimately, these perturbations synergize in their disruption of metabolism and energy homeostasis, arguably among the key medical challenges of the twenty

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Esther Isorna Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain

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Nuria de Pedro Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain

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Ana I Valenciano Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain

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Ángel L Alonso-Gómez Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain

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María J Delgado Departamento de Fisiología (Fisiología Animal II), Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain

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& Mistlberger 2013 ) and temperature cycles ( Buhr et al. 2010 , Poletini et al. 2015 , Schibler et al. 2015 ) are also important. These environmental factors are considered the ‘inputs’ of the circadian system, whereas the rhythms that are generated are

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Jennifer A Evans Department of Biomedical Sciences, Marquette University, Milwaukee, WI, USA

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timing of these rhythms is programed by a biological clock and influenced by sleep ( Czeisler & Klerman 1999 ). Over the last few decades, we have gained a deep understanding of the mechanisms that produce circadian timekeeping at the molecular and

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Shannon M Bailey Division of Molecular and Cellular Pathology, Division of Cardiovascular Diseases, Department of Pathology

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Uduak S Udoh Division of Molecular and Cellular Pathology, Division of Cardiovascular Diseases, Department of Pathology

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Martin E Young Division of Molecular and Cellular Pathology, Division of Cardiovascular Diseases, Department of Pathology

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becoming increasingly clear is that behavior-independent endogenous mechanisms also contribute toward daily rhythms in metabolism; one such mechanism is the cell autonomous circadian clock, which allows the cell to anticipate a predictable daily stimulus

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Jonathan D Johnston Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK

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Debra J Skene Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK

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both circadian time and day-length, enabling it to influence both daily and seasonal rhythms in many species. Melatonin is synthesised by multiple tissues in the body, but the pineal gland is the major contributor to circulating melatonin concentration

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Jodi L Downs Division of Neuroscience, Oregon National Primate Research Center, Beaverton, Oregon 97006 and Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239, USA

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Henryk F Urbanski Division of Neuroscience, Oregon National Primate Research Center, Beaverton, Oregon 97006 and Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239, USA

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rhythmicity or an attenuation of the amplitude of many circadian rhythms appears to be a characteristic of aging ( Schwartz 1993 , Touitou et al. 1997 , Touitou & Haus 2000 , Downs et al. 2001 , Pandi-Perumal et al. 2002 , Urbanski et al. 2004

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Isis Gabrielli Barbieri de Oliveira Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Marcos Divino Ferreira Junior Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Paulo Ricardo Lopes Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Dhiogenes Balsanufo Taveira Campos Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Marcos Luiz Ferreira-Neto Departament of Physiology, Institute of Biomedical Science, Laboratory of Electrophysiology and Cardiovascular Physiology, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil

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Eduardo Henrique Rosa Santos Departament of Physiology, Institute of Biomedical Science, Laboratory of Electrophysiology and Cardiovascular Physiology, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil

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Paulo Cezar de Freitas Mathias Department of Biotechnology, Genetics and Cell Biology, Laboratory of Secretion Cell Biology, State University of Maringá, Maringá, Paraná, Brazil

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Flávio Andrade Francisco Department of Biotechnology, Genetics and Cell Biology, Laboratory of Secretion Cell Biology, State University of Maringá, Maringá, Paraná, Brazil

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Bruna Del Vechio Koike Medical Department, Federal University of San Francisco Valley, Petrolina, Pernambuco, Brazil

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Carlos Henrique de Castro Department of Physiological Science, Integrative Laboratory of Cardiovascular and Neurological Pathophysiology, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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André Henrique Freiria-Oliveira Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Gustavo Rodrigues Pedrino Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Rodrigo Mello Gomes Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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Daniel Alves Rosa Center of Neuroscience and Cardiovascular Research, Biological Science Institute, Federal University of Goiás, Goiânia, Goiás, Brazil

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relate to increased adiposity and the development of other parameters of metabolic syndrome ( Báez-Ruiz et al. 2017 ). Although many evidence suggests that the desynchronization of circadian rhythm increases the risk of cardiometabolic disorders

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