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The circadian rhythms of most night shift workers do not adapt fully to the imposed behavioural schedule, and this factor is considered to be responsible for many of the reported health problems. One way in which such disturbances might be mediated is through inappropriate hormonal and metabolic responses to meals, on the night shift. Twelve healthy subjects (four males and eight females) were studied on three occasions at the same clock time (1330 h), but at different body clock times, after consuming test meals, first in their normal environment, secondly after a forced 9 h phase advance (body clock time approximately 2230 h) and then again 2 days later in the normal environment. They were given a low-fat pre-meal at 0800 h, then a test meal at 1330 h with blood sampling for the following 9 h. Parameters measured included plasma glucose, non-esterified fatty acids (NEFAs), triacylglycerol (TAG), insulin, C-peptide, proinsulin and glucose-dependent insulinotropic polypeptide, and urinary 6-sulphatoxymelatonin. In contrast with a previous study with a high-fat pre-meal, postprandial glucose and insulin responses were not affected by the phase shift. However, basal plasma NEFAs were lower immediately after the phase shift (P < 0.05). Incremental (difference from basal) TAG responses were significantly higher (P < 0.05) immediately after the phase shift compared with before. Two-day post-phase shift responses showed partial reversion to baseline values. This study suggests that it takes at least 2 days to adapt to eating meals on a simulated night shift, and that the nutritional content of the pre-meals consumed can have a marked effect on postprandial responses during a simulated phase shift. Such findings may provide a partial explanation for the increased occurrence of cardiovascular disease reported in shift workers.
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The secretion of corticotrophin releasing activity (CRA) from the isolated rat hypothalamus incubated in vitro was investigated under various conditions of incubation and of pretreatment of donor animals providing hypothalami. Media from hypothalamic incubations were assayed for CRA by a validated double in-vitro bioassay technique which differentiates CRA from vasopressin.
A circadian rhythm was found in the secretion of CRA in vitro from isolated hypothalami obtained from animals killed at different times of the day. Secretion of CRA increased significantly at 19.00 h (dusk) compared with the secretion rate at 07.00 h, in synchrony with a rise in plasma corticosterone levels. In addition, both plasma corticosterone concentrations and CRA secretion in vitro were higher at 07.00 h than at 19.00 h after exposure of the donor animals to a reversed light cycle for 7–10 days.
Hypothalami obtained from animals chronically treated with betamethasone in the drinking water showed a diminished secretion of CRA in vitro. Exposure of untreated animals to ether vapour for 2 min immediately before death significantly increased the subsequent secretion of CRA in vitro. Ether exposure did not significantly affect the secretion of CRA in vitro from hypothalami of betamethasone-treated rats. There was a close correlation between plasma corticosterone levels and in-vitro CRA release after these treatments. The results suggest that the secretion of CRA examined in this way is a phenomenon which can reflect the changes which occur in the activity of the hypothalamo-pituitary-adrenal system in vivo during the 24-h cycle, after glucocorticoid treatment and after ether stress.
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Circulating concentrations of leptin in sheep correlate with body fatness and are affected by level of food intake and photoperiod. The present objective was to elucidate the short-term dynamics of leptin secretion. Frequent blood samples were taken over 48 h from 12 Soay rams after 16 weeks in short-day photoperiod (SD, 16 h darkness:8 h light) with freely available food, and then after 16 weeks in long days (16 h light:8 h darkness) with food freely available (LD) or restricted to 90% maintenance (LDR) (n=6/group). During the second 24 h of sampling, half were food deprived (n=6, SD and LD) and half had their meal times shifted (n=6, SD and LDR). A homologous RIA was developed, using antibodies raised in chicken against recombinant ovine leptin, to measure plasma concentrations. Simultaneous 24 h profiles of plasma insulin, glucose and non-esterified fatty acids (NEFA) were measured. Plasma leptin was higher in LD than SD, and in LD than LDR, associated with higher food intake, liveweight and body condition score (adiposity), but tended to be lower in LDR than SD, associated with lower food intake, liveweight and body condition score. There was no evidence for a circadian rhythm of plasma leptin, but clear evidence for post-prandial peaks of low amplitude (15-36%) 2-8 h after meals given at normal and shifted times. Complete food deprivation caused a dramatic fall in plasma leptin to basal levels within 24 h. There was a positive association of plasma leptin with plasma insulin, and negative association with NEFA, both between meals and during fasting. Thus, plasma leptin concentrations in sheep are sensitive to short-term changes in energy balance, as well as to long-term photoperiod-driven changes in food intake and adiposity.
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ABSTRACT
We studied 24-h hormone profiles and hormonal responses to insulin-induced hypoglycaemia prospectively in 23 children of similar age and pubertal stage, nine of whom had received prior cranial irradiation (group 1) and fourteen of whom had not (group 2), before and 6–12 months after total body irradiation (TBI) for bone marrow transplantation in leukaemia.
Fourier transformation demonstrated that group 1 children had a faster periodicity of GH secretion before TBI than group 2 children (160 vs 200 min) but the amplitude of their GH peaks was similar. There were no differences between the groups in circadian cortisol rhythm, serum concentrations of insulin-like growth factor-I (IGF-I), sex steroids and basal thyroxine (T4). The peak serum GH concentrations observed after insulin-induced hypoglycaemia were similar between the two groups but the majority of patients had blunted responses.
TBI increased the periodicity of GH secretion in both groups (group 1 vs group 2; 140 vs 180 min), but the tendency to attenuation of amplitude was not significant. There were no significant changes in the peak serum GH concentration response to insulin-induced hypoglycaemia which remained blunted. Serum IGF-I, sex steroid, cortisol or T4 concentrations were unchanged.
Low-dose cranial irradiation has an effect on GH secretion affecting predominantly frequency modulation leading to fast frequency, normal amplitude GH pulsatility. This change is accentuated by TBI. In patients with leukemia, there is a marked discordance between the peak serum GH response to insulin-induced hypoglycaemia compared with the release of GH during 24-h studies, irrespective of the therapeutic regimen used. Pharmacological assessment of GH reserve needs to be interpreted with caution in such situations.
Journal of Endocrinology (1993) 136, 331–338
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SUMMARY
The incorporation of [35S]methionine into protein of the anterior pituitary and discrete brain areas was measured following the administration of antibodies to oestrogen, ovariectomy, or adrenalectomy on the afternoon of dioestrus. The antibody to oestrogen deleted the circadian rhythms of methionine incorporation normally observed in the various brain areas together with the peaks of incorporation normally observed in the median eminence area and anterior pituitary on the evening of pro-oestrus. The peaks of incorporative activity normally observed in the preoptic area and amygdala (relative to the putamen) at 03.00 h on the day of pro-oestrus were also deleted. Administration of the antiserum on the morning of pro-oestrus failed to alter the pattern of methionine incorporation normally observed on the evening of pro-oestrus.
Ovariectomy performed at 16.00 h of dioestrus blocked the preovulatory rise of luteinizing hormone (LH) (as did the antibody to oestrogen) and inhibited the peak of methionine incorporation normally observed in the anterior pituitary on the evening of pro-oestrus. However, for the peak in the median eminence to be inhibited, ovariectomy had to be performed on the morning of the preceding oestrus. Adrenalectomy alone, or adrenalectomy with ovariectomy, performed on the afternoon of dioestrus did not affect the levels of methionine incorporation in the brain or anterior pituitary at 18.00 h on the day of prooestrus.
Animals which had been ovariectomized and injected with 2·5 μg oestradiol benzoate on the morning of oestrus showed significantly increased levels of methionine incorporation in all the brain areas and the anterior pituitary at 18.00 h of expected pro-oestrus. The administration of antibody to oestrogen to a similar group of animals on the afternoon of expected dioestrus inhibited the rise at 18.00 h of expected pro-oestrus. The apparent discrepancy between the results obtained with ovariectomy and the antiserum appeared to be due to the ability of the antiserum to neutralize the activity of oestrogens retained by the tissues.
The present results suggest that the changes in incorporation of methionine into protein in the brain and anterior pituitary are brought about by the action of endogenous oestrogen: there appears to be a steady summative effect on the median eminence throughout the oestrous cycle together with a short-lived effect occurring during pro-oestrus and affecting the anterior pituitary.
Department of Physiology, The University of Melbourne, Parkville, Victoria, Australia
Tufts Medical Center, Boston, Massachusetts, USA
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Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford, UK
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peripheral tissue to anticipate environmental stimuli ( Takahashi & Zatz 1982 ). The GR and MR are not expressed in the SCN but the GR serves as a zeitgeber of the circadian clock in peripheral tissues ( Kino & Chrousos 2011 a ). Circadian rhythm is driven
Third Faculty of Medicine, Charles University, Prague, Czech Republic
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production and composition of CSF follows a daily rhythm ( Nilsson et al. 1992 , Harrington et al. 2010 ). The mechanism of these rhythmic changes is not known but recently, the CP cells were found to harbor a robust circadian clock ( Quintela et al
Molecular Medicine Research Labs, Drug Discovery Research, Astellas Pharma Inc., Miyukigaoka 21, Tsukuba-shi, Ibaraki 305-8585, Japan
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Molecular Medicine Research Labs, Drug Discovery Research, Astellas Pharma Inc., Miyukigaoka 21, Tsukuba-shi, Ibaraki 305-8585, Japan
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Molecular Medicine Research Labs, Drug Discovery Research, Astellas Pharma Inc., Miyukigaoka 21, Tsukuba-shi, Ibaraki 305-8585, Japan
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Molecular Medicine Research Labs, Drug Discovery Research, Astellas Pharma Inc., Miyukigaoka 21, Tsukuba-shi, Ibaraki 305-8585, Japan
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Molecular Medicine Research Labs, Drug Discovery Research, Astellas Pharma Inc., Miyukigaoka 21, Tsukuba-shi, Ibaraki 305-8585, Japan
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, which is critical for successful pregnancy in rodents ( Gu et al. 1994 ). The present finding predicts that, in vivo , the circadian rhythms in the endometrial stroma may be impaired during decidualization. In vivo , cellular differentiation
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consider some of the molecular mechanisms known to drive LD responses, and their regulation by the circadian clock. Circannual rhythms are also dominant characteristic of the reproductive biology of many tropical species. For instance, even when species
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Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, College of Engineering, Wellcome Trust Centre for Biomedical Modelling and Analysis, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, College of Engineering, Wellcome Trust Centre for Biomedical Modelling and Analysis, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
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Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, College of Engineering, Wellcome Trust Centre for Biomedical Modelling and Analysis, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
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glucocorticoid ultradian rhythm. (a) Stress and circadian inputs activate the hypothalamic PVN to release CRH and AVP into the hypothalamic–pituitary portal circulation. CRH and AVP activate corticotroph cells in the anterior pituitary, which respond with the
