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G. E. Webley, H. Mehl, and K. P. Willey


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, Y. Touitou, A. Restoin, C. Migraine, F. Levi, and H. Montagner


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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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

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, Nuria de Pedro, Ana I Valenciano, Ángel L Alonso-Gómez, and María J Delgado

& 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

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, Uduak S Udoh, and Martin E Young

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 and Debra J Skene

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 and Henryk F Urbanski

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, Marcos Divino Ferreira Junior, Paulo Ricardo Lopes, Dhiogenes Balsanufo Taveira Campos, Marcos Luiz Ferreira-Neto, Eduardo Henrique Rosa Santos, Paulo Cezar de Freitas Mathias, Flávio Andrade Francisco, Bruna Del Vechio Koike, Carlos Henrique de Castro, André Henrique Freiria-Oliveira, Gustavo Rodrigues Pedrino, Rodrigo Mello Gomes, and Daniel Alves Rosa

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