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

same daily rhythmicity in its synthesis as observed for pineal melatonin. However, these daily patterns are particular to each species. For example, in goldfish, gut melatonin synthesis shows a clear circadian rhythm that is in phase with that of the

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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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The uptake of radioactive phosphorus by the pineal gland in White Leghorn cockerels (Gallus domesticus) showed a diurnal variation with maxima in the light phase and minima in the dark phase of the light:dark cycle. Constant light caused the rhythm to disappear while constant dark had no effect other than lowering the amplitude of the variations. These data indicate that the rhythm in pineal uptake of 32P is circadian.

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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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Cátia F Gonçalves and Qing-Jun Meng

clocks present in most of the cell types in cartilage and bone ( Dudek & Meng 2014 , Yang & Meng 2016 ). Alterations in the circadian rhythm of skeletal biology are associated with the development of various disorders, including osteoarthritis (OA

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Pei-Jian He, Masami Hirata, Nobuhiko Yamauchi, and Masa-aki Hattori

Introduction Circadian rhythm is generated by genetically determined biological clock, and is prominently entrained by cues from the 24-h light:darkness cycle ( Dunlap 1999 , Reppert & Weaver 2001 ). In mammals, the central clock is

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Adrenocorticotrophin (ACTH) and corticosterone in the plasma of adult female rats were measured sequentially at 4 h intervals for 24 h before and after lesions of the suprachiasmatic nuclei or treatment with p-chlorophenylalanine (to inhibit serotonin synthesis). After lesions or p-chlorophenylalanine treatment, the concentrations of ACTH were diminished relative to those in control animals and rhythmic changes could not be detected. However, injection of animals, pretreated with p-chlorophenylalanine, with 5-hydroxytryptophan (60 mg/kg) 8 h before the time when plasma ACTH is maximal in intact animals, stimulated ACTH secretion up to control values. Mean corticosterone concentrations in plasma remained unchanged (after lesions) or increased (after p-chlorophenylalanine). This increase was associated with an increased minimal concentration of corticosterone. After both treatments there was evidence of continued circadian or ultradian rhythms of corticosterone concentration.

Locomotor activity of female rats given identical treatment, but without blood sampling, indicated that nocturnal activity was diminished after lesions whereas diurnal activity was enhanced after p-chlorophenylalanine treatment. Periodicity analysis detected the persistence of free-running circadian, and sometimes ultradian activity, rhythms. Adrenalectomy did not alter further the activity pattern observed in rats with lesions.

These results therefore support the proposition that both the suprachiasmatic nuclei and the serotoninergic system play an irreplaceable role in the mechanism of ACTH secretory rhythms. The suprachiasmatic nuclei are also important for synchronization of locomotor activity and corticosterone rhythms, which may both persist after the suppression of ACTH rhythms.

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Henrik Oster

– 40–50% across the whole body – are expressed with a circadian rhythm ( Zhang et al. 2014 ). Of note, just like the delayed-action GC-mediated stress response, circadian clock regulation acts through slow, transcription

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Shanqi Fu, Miho Kuwahara, Yoko Uchida, Sei Kondo, Daichi Hayashi, Yuji Shimomura, Asami Takagaki, Takashi Nishida, Yusuke Maruyama, Mika Ikegame, Atsuhiko Hattori, Satoshi Kubota, and Takako Hattori

receptors and developmental control genes ( Reddi 1994 , Goldring et al. 2006 , Shao et al. 2006 , Liu et al. 2017 ). There is considerable evidence to suggest that cartilage and bone growth in vertebrates oscillate in a circadian rhythm, but the

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S A Cavigelli, S L Monfort, T K Whitney, Y S Mechref, M Novotny, and M K McClintock

several pellets every 1–2 h ( Kishibayashi et al. 1995 ), according the higher temporal resolution needed to detect circadian rhythms and perturbations by a stressor. Fecal corticoid measures are also effective for documenting changes in glucocorticoid