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      Time of Day-Dependent Effects of Thyroliberin and Thyrotropin on Thymocyte Proliferation in Rats



      S. Karger AG

      Thyrotropin, Thyroliberin, Thymocytes, Cell proliferation, Chronobiology

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          Our earlier studies have shown that thyroliberin (TRH) as well as thyrotropin (TSH) enhanced thymus cell proliferation. The aim of the present study was to investigate whether the effects of TRH and TSH on thymocyte proliferation depend on time of day. A single subcutaneous injection of TRH (25 μg/animal) or TSH (3 IU/animal) was made at 9:00 h (1 h after light onset) or at 18:00 h (10 h after light onset) in 3-month-old male Wistar rats. The animals were killed 24 h later. The proliferation of thymocytes was assessed by incorporation of bromodeoxyuridine into cell nuclei. Thymocyte proliferation was significantly increased by TSH administration at 9:00 h, whereas treatment given at 18:00 h was ineffective. TRH enhanced the proliferation when injected at 9:00 h, but had an inhibitory effect when administered at 18:00 h. These data indicate that the effects of TRH and TSH on thymocyte proliferation are dependent on time of day.

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          The involvement of pineal gland and melatonin in immunity and aging. I. Thymus-mediated, immunoreconstituting and antiviral activity of thyrotropin-releasing hormone.

          Circadian, continued treatment with melatonin during the dark cycle produces changes in the blood level of thyroid hormones in aging mice. Thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) antagonize the involution of the thymus produced by prednisolone. This effect of TRH does not seem thyroid dependent. TRH restores antibody production in non-responder athymic nude mice but does not exert this effect in neonatally thymectomized mice. Moreover, this activity does not correlate with thyroxine levels. TRH exerts a powerful protective effect in mice challenged with encephalomyocarditis (EMC) virus. Presumably pineal melatonin exerts its varied regulatory functions via hypothalamic TRH.

            Author and article information

            S. Karger AG
            February 1999
            18 February 2000
            : 7
            : 2
            : 89-91
            Department of Experimental Endocrinology and Hormone Diagnostics, Institute of Endocrinology, Medical University of Lodz, Poland
            26425 Neuroimmunomodulation 2000;7:89–91
            © 2000 S. Karger AG, Basel

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            Figures: 2, References: 21, Pages: 3
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