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Taira Wada, Yukiko Yamamoto, Yukiko Takasugi, Hirotake Ishii, Taketo Uchiyama, Kaori Saitoh, Masahiro Suzuki, Makoto Uchiyama, Hikari Yoshitane, Yoshitaka Fukada, and Shigeki Shimba

rhythms ( Kohsaka et al. 2007 ). The levels of several hormones and cytokines show a circadian rhythm ( Andrews & Folk 1964 , Barter et al. 1971 , Vaughan et al. 1976 , Kaneko et al. 1980 , Arvidson et al. 1994 , Sinha et al. 1996

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Anjara Rabearivony, Huan Li, Shiyao Zhang, Siyu Chen, Xiaofei An, and Chang Liu

timing signals for living organisms on Earth. Consequently, according to these signals, the endogenous circadian rhythms within organisms are entrained to the solar day ( Pittendrich 1960 , Refinetti 2010 , Fonken et al. 2013 ). While the central

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Silvia Begliuomini, Elena Lenzi, Filippo Ninni, Elena Casarosa, Sara Merlini, Nicola Pluchino, Valeria Valentino, Stefano Luisi, Michele Luisi, and Andrea R Genazzani

there are no studies at present in the literature investigating a possible BDNF circadian rhythm in humans, we studied the BDNF levels throughout 24 h in healthy men, in order to detect the possible relative changes in plasma BDNF protein. Additionally

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Department of Animal Science, University of California, Davis, California 95616, U.S.A.

(Received 8 October 1974)

Few studies have dealt with diurnal cortisol rhythm in sheep (McNatty, Cashmore & Young, 1972; McNatty & Young, 1973). The present results elucidate further the circadian rhythm of ovine plasma cortisol and describe the effect of sudden and continuous cage restraint.

Experimental methods and conditions were reported in detail by Holley & Evans (1974). Six mature rams were sampled at 4 h intervals for 32 days. On day 17 the animals were placed singly in small cages. Throughout the experiment the sheep received lucerne pellets at 16.00 h and the lighting schedule was maintained at 14 h light: 10 h darkness. Plasma cortisol was determined in duplicate without correction for other steroids as described by Bassett & Hinks (1969) and adjusted for extraction efficiency.

Fig. 1. Daily percentage variations (means ± s.e.m.) in plasma cortisol

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Pharmacological doses of glucocorticoids inhibit thyroid function in man and laboratory animals due to suppression of thyrotrophin (TSH) secretion (Wilber & Utiger, 1969). Administration of prednisolone or dexamethasone for 1–2 days results in a suppression of basal serum TSH levels in normal subjects and in patients with primary hypothyroidism, whilst the pituitary TSH reserve capacity, as assessed by the response to synthetic thyrotrophin releasing hormone (TRH), remains unaltered (Wilber & Utiger, 1969; Besser, Ratcliffe, Kilborn, Ormston & Hall, 1971; Haigler, Pittman & Hershman, 1971). However, impairment of serum TSH response to administered TRH does occur in patients treated with glucocorticoids for 1 or more months (Otsuki, Dakoda & Baba, 1973). These studies suggest that glucocorticoids may inhibit TSH secretion at both hypothalamic and pituitary levels but the main effect of the short-term treatment is suppression of TRH production.

Nicoloff, Fisher & Appleman (1970) found that the circadian rhythm of thyroidal

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Marianna Minnetti, Valeria Hasenmajer, Riccardo Pofi, Mary Anna Venneri, Krystallenia I Alexandraki, and Andrea M Isidori

adrenal hormones play a pivotal role in mitigating or enhancing the effects of clock genes on their own targets. The exact role of glucocorticoids in this context has yet to be fully elucidated. However, it is generally accepted that their circadian rhythm

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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

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Muneki Ikeda, Yasushi Hojo, Yoshimasa Komatsuzaki, Masahiro Okamoto, Asami Kato, Taishi Takeda, and Suguru Kawato

), the CORT level changes in both the plasma and brain along the circadian rhythm ( Migeon et al . 1956 , Moore & Eichler 1972 , Qian et al . 2012 ). Qian et al . showed the high synchronicity of CORT oscillation between the blood and hippocampus by

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J Fahrenkrug, B Georg, J Hannibal, and H L Jørgensen

thyroid hormones compared to control rats, and based on the mean concentrations, it amounted to 7.7-fold for T4, 23-fold for free T4 and two-fold for T3, respectively ( Fig. 4D, E and F ). Furthermore, daily circadian rhythms in the thyroid hormones

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Roberto Dominguez, Laura Riboni, Domingo Zipitria, and Rodolfo Revilla

Rats with a 4-day oestrous cycle were given a single dose of atropine (100, 300, 500 or 700 mg/kg body wt) at 13.00 h on the days of oestrus, dioestrus 1, dioestrus 2 or pro-oestrus and were autopsied on the next expected day of oestrus. The doses of atropine (in mg/kg body wt) necessary to block ovulation during the cycle were 300 at oestrus, 100 at dioestrus 1 or 2 and 700 at pro-oestrus. A single dose of atropine (100 mg/kg) at oestrus, dioestrus 1 or dioestrus 2 was given at 09.00, 13.00, 17.00 or 21.00 h, autopsy again being performed on the next expected day of oestrus. The ability of atropine to block ovulation appeared to have a circadian rhythm, with a maximum blockade at 13.00 h on dioestrus 1 and dioestrus 2 and a minimum at 21.00 h on the same days. Hormone replacement (human chorionic gonadotrophin at oestrus, dioestrus 1 or 2, oestradiol benzoate at dioestrus 2 or progesterone at pro-oestrus) re-established normal ovulation in rats whose ovulation was blocked with atropine (100 mg/kg) on dioestrus 1 at 13.00 h. When ovulation was blocked with atropine but no hormone replacement had been given, rats ovulated 24 h after the next expected day of oestrus.

Results obtained in these experiments suggest the existence of a circadian rhythm of gonadotrophin secretion thoughout the oestrous cycle and a close relationship between that rhythm and the cholinergic system.