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This Article Accepted manuscript (PDF) All Versions of this Article: JOE-08-0125v1 198/1/119    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Araujo, R. Articles by Pires de Carvalho, D. Search for Related Content PubMed PubMed Citation Articles by Araujo, R. Articles by Pires de Carvalho, D., MD, PhD

R Araujo, Laboratorio de Fisiologia Endocrina, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
B Andrade, Laboratorio de Fisiologia endocrina, Instituto de Biofisica Carlos chagas Filho, Rio de Janeiro, Brazil
A Padron, Laboratorio de Fisiologia Endocrina, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
M Marassi, Laboratorio de Fisiologia Endocrina, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
V Pereira, Laboratorio de Fisiologia Endocrina, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
M Leandro, Laboratorio de Fisiologia Endocrina, Instituto de Biofisica Carlos Chagas Filho, Rio de Janeiro, Brazil
E Bouskela, Laboratrio de Pesquisas em Microcirculacao, UERJ, Instituto de Biologia Roberto Alcantara Gomes, Rio de Janeiro, Brazil
D Pires de Carvalho, Instituto de Biofisica Carlos Chagas Filho, UFRJ, Rio de Janeiro, 21949900, Brazil

Correspondence: Denise Pires de Carvalho, Email: dencarv{at}biof.ufrj.br

Abstract

During food restriction, decreased basal metabolic rate secondary to reduced serum thyroid hormones levels contributes to weight loss resistance. Thyroxine (T4) or 3,3or 3,3’,5 - tri-iodo-thyronine (T3) administration during caloric restriction produce deleterious side effects; however the administration of physiological doses of T4 during food restriction has never been evaluated. The aim of this study was analyze the effects of low replacement doses of T4 in Wistar rats submitted to 40% food restriction. 30 days of food restriction led to significantly reduced liver type 1 deiodinase activity, serum TSH, leptin, T4, T3, metabolic rate and body mass. The significant reduction in hepatic deiodinase activity found during food restriction was normalized in a dose dependent manner by T4 replacement, showing that decreased D1 activity is secondary to decreased serum thyroid hormone levels during caloric restriction. The lowest replacement dose of T4 did not normalize resting metabolic rate (RMR), but was able to potentiate the effects of food restriction on fat carcass loss and did not spare body protein. The highest dose of T4 produced a normalization of daily oxygen consumption and determined a significant reduction in both carcass fat and protein content. Our results show that serum T4 normalization during food restriction restores serum T3 and liver D1 activity, while body protein is not spared. Thus, decreased serum T4 during caloric restriction corresponds to a protective mechanism to avoid body protein loss, highlighting the importance of other strategies to reduce body mass without lean mass loss.