Document Detail

A test of the hypothesis that T3 is the "seasonality" thyroid hormone in American tree sparrows (Spizella arborea): intracerebroventricular infusion of iopanoic acid, an inhibitor of T3 synthesis and degradation.
MedLine Citation:
PMID:  11302527     Owner:  NLM     Status:  MEDLINE    
This study tested the hypothesis that L-3,5,3'-triiodothyronine (T3) is the bioactive "seasonality" thyroid hormone in American tree sparrows (Spizella (arborea). The experimental approach coupled thyroid hormone replacement therapy after radiothyroidectomy with photostimulation and intracerebroventricular infusion of iopanoic acid, an inhibitor of L-3,5,3'-triiodothyronine synthesis and degradation. Endpoints were testis length, molt score, and hypothalamic content of chicken gonadotropin-releasing hormone 1. The hypothesis predicts that thyroidectomized male tree sparrows moved to long days and given thyroxine in combination with iopanoic acid will lack L-3,5,3'-triiodothyronine and so will not express thyroid hormone-dependent photoperiodic testicular growth (a vernal component of seasonality) and photorefractoriness or postnuptial molt (autumnal components of seasonality). It further predicts that iopanoic acid will enhance the efficacy of L-3,5,3'-triiodothyronine and so will facilitate the expression of seasonality in thyroidectomized males given L-3,5,3'-triiodothyronine replacement therapy. Iopanoic acid had no significant effect on any component of seasonality in thyroid-intact males given vehicle, or in thyroidectomized males given thyroxine or L-3,5,3'-triiodothyronine. Thyroid-intact males, as well as thyroidectomized males infused with thyroxine alone, commonly expressed all components of seasonality. Thyroidectomized males given L-3,5,3'-triiodothyronine alone exhibited photoperiodic testicular growth, but did not become photorefractory or initiate molt. While these results confirm that thyroid hormone acts centrally to program American tree sparrows for seasonality, they do not support the hypothesis that L-3,5,3'-triiodothyronine is the bioactive "seasonality" thyroid hormone, and they challenge the view that thyroxine is merely a prohormone.
F E Wilson
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology     Volume:  171     ISSN:  0174-1578     ISO Abbreviation:  J. Comp. Physiol. B, Biochem. Syst. Environ. Physiol.     Publication Date:  2001 Mar 
Date Detail:
Created Date:  2001-04-13     Completed Date:  2001-08-02     Revised Date:  2009-06-08    
Medline Journal Info:
Nlm Unique ID:  8413200     Medline TA:  J Comp Physiol B     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  113-9     Citation Subset:  IM    
Division of Biology, Kansas State University, Manhattan 66506-4901, USA.
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MeSH Terms
Brain Chemistry / drug effects,  physiology
Contrast Media / pharmacology
Injections, Intraventricular
Iopanoic Acid / pharmacology
Songbirds / physiology*
Testis / drug effects,  physiology
Thyroid Gland / physiology,  surgery
Thyroxine / pharmacology
Triiodothyronine / biosynthesis,  metabolism*
Reg. No./Substance:
0/Contrast Media; 6893-02-3/Triiodothyronine; 7488-70-2/Thyroxine; 96-83-3/Iopanoic Acid

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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