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      Effect of Repeated Stimulation by Thyrotropin-Releasing Hormone (TRH) on Thyrotropin and Prolactin Secretion in Perfused Euthyroid and Hypothyroid Rat Pituitary Fragments

      ,

      Hormone Research in Paediatrics

      S. Karger AG

      Hypothyroid, Pituitary, Thyrotropin, Prolactin, TRH, Perfusion, Euthyroid

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          Abstract

          The previously reported refractoriness of pituitary response to thyrotropin-releasing hormone (TRH) stimuli was investigated here in an in vitro perfusion system using pituitary tissue from euthyroid and hypothyroid rats. Thyroid-stimulating hormone (TSH) and prolactin (PRL) responses to TRH (28 pmol) were significantly greater in hypothyroid tissue compared with euthyroid. Hypothyroid tissue showed a reduction in response to two consecutive stimuli in both TSH and PRL, however the TSH decline in response was more marked than PRL. Euthyroid tissue showed no significant decline in response to TRH. An increase in the dose of TRH (112 pmol), administered to euthyroid tissue, resulted in increased TSH and PRL response, but no decline in response to sequential stimuli was observed. Three consecutive stimuli by TRH (28 pmol) of hypothyroid tissue resulted in a consistent decline in TSH response. The decline in PRL response only reached statistical significance by the third stimulation. Euthyroid and hypothyroid pituitary tissue was subjected to sequential depolarising stimulation with KCl (50 µmol). Euthyroid tissue showed no decline in response in either TSH or PRL. In hypothyroid tissue only, the decline in TSH response reached statistical significance. This decline in TSH response was significantly smaller than the decline in response observed in hypothyroid tissue stimulated with TRH. Refractoriness of hypothyroid pituitary tissue to repeated TRH stimuli is reported here. Our data suggest that the decline in hormonal response cannot be explained solely on the basis of tissue depletion.

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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
          1984
          1984
          26 November 2008
          : 20
          : 4
          : 269-276
          Affiliations
          Department of Medicine, University of Birmingham, Queen Elizabeth Hospital, Birmingham, UK
          Article
          180007 Horm Res 1984;20:269–276
          10.1159/000180007
          6439618
          © 1984 S. Karger AG, Basel

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          Pages: 8
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