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      Acute and Transient Activation of Pituitary-Thyroid Axis during Unforced Restriction in Rats: Component of Nonshivering Thermogenesis in Conscious Animals ?

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          Abstract

          Groups of 6–8 male Wistar Olac SPF rats weighing about 300 g were subjected to unforced restriction (UR) in small cages with a metallic bottom and a Plexiglas cover for various intervals from 2 min to 72 h. An acute activation of the pituitary-thyroid axis was found which was manifested by an increase of thyrotropin (TSH) and thyroxine (T<sub>4</sub>) levels at 2–5 min of UR. This was presumably due to the emotional effect of a rapid transfer and to the placing of the animals into restriction cages. Later, between 3 and 6 h of UR, another, and more pronounced period of activation of the pituitary-thyroid axis and of the peripheral thyroid hormone metabolism was repeatedly observed which lasted until about 36–48 h and was manifested by a highly significant increase of TSH, T<sub>4</sub>, 3,5,3’-triiodothronine (T<sub>3</sub>) and 3,3’,5’-triiodothyronine (rT<sub>3</sub>) levels. It was concluded that this phenomenon presumably may be a component of nonshivering thermogenesis resulting from a decreased muscular activity and resembling the conditions occurring under cold stress. Such a view was supported by findings of highly increased nonesterified fatty acid levels in plasma in restricted animals, by unchanged levels of TSH and thyroid hormones found in unrestricted animals kept individually in regular group cages and, finally, by a preventive effect of ambient temperature of 32 °C on the pituitary-thyroid activation at 6 h of UR. In some experiments, no substantial differences in hormone levels were found between the animals kept in Plexiglas or stainless wire-mesh restriction cages. Finally, a multifold increase of prolactin level in plasma was found as early as 2 min of UR, the peak being observed between 5 and 20 min and a decrease to about the initial level at about 360 min.

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          Author and article information

          Journal
          HRE
          Horm Res Paediatr
          10.1159/issn.1663-2818
          Hormone Research in Paediatrics
          S. Karger AG
          1663-2818
          1663-2826
          1983
          1983
          26 November 2008
          : 17
          : 1
          : 27-35
          Affiliations
          Institute of Experimental Endocrinology, Center of Physiological Sciences SAV, Bratislava, Czechoslovakia
          Article
          179671 Horm Res 1983;17:27–35
          10.1159/000179671
          6840669
          © 1983 S. Karger AG, Basel

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          Pages: 9
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