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ORIGINAL RESEARCH ARTICLE

Neonatal Low-Protein Diet Changes Deiodinase Activities and Pituitary TSH Response to TRH in Adult Rats

P. C. Lisboa^*,1, A. T. S. Fagundes^*, A. T. A. Denolato^*, E. Oliveira^*, I. T. Bonomo^*, S. B. Alves^*, F. H. Curty^*, M. C. F. Passos and E. G. Moura^*

^* Departmento de Ciências Fisiológicas, Instituto de Biologia Roberto Alcântara Gomes, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brasil 20551-030; Departmento de Nutrição Aplicada, Instituto de Nutrição, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brasil 20551-030

To whom requests for reprints should be addressed at ¹ Departamento de Ciências Fisiológicas, 5° andar, Instituto de Biologia, Universidade do Estado do Rio de Janeiro, Av. 28 de setembro, 87, Rio de Janeiro, RJ, 20551-030, Brazil. E-mail: pclisboa{at}uerj.br or patricialisboa{at}pq.cnpq.br

Protein malnutrition during neonatal programs for a lower body weight and hyperthyroidism in the adult offspring were analyzed. Liver deiodinase is increased in such animals, contributing to the high serum triiodothyronine (T3) levels. The level of deiodinase activities in other tissues is unknown. We analyzed the effect of maternal protein restriction during lactation on thyroid, skeletal muscle, and pituitary deiodinase activities in the adult offspring. For pituitary evaluation, we studied the in vitro, thyrotropin-releasing hormone (TRH)–stimulated thyroid-stimulating hormone (TSH) secretion. Lactating Wistar rats and their pups were divided into a control (C) group, fed a normal diet (23% protein), and a protein-restricted (PR) group, fed a diet containing 8% protein. At weaning, pups in both groups were fed a normal diet until 180 days old. The pituitary gland was incubated before and after TRH stimulation, and released TSH was measured by radioimmunoassay. Deiodinase activities (D1 and D2) were determined by release of ¹²⁵I from [¹²⁵I]reverse triiodothyronine (rT3). Maternal protein malnutrition during lactation programs the adult offspring for lower muscle D2 (– 43%, P <0.05) and higher muscle D1 (+83%, P <0.05) activities without changes in thyroidal deiodinase activities, higher pituitary D2 activity (1.5 times, P <0.05), and lower TSH response to in vitro TRH (– 56%, P <0.05). The evaluations showed that the lower in vivo TSH detected in adult PR hyperthyroid offspring, programmed by neonatal undernutrition, may be caused by an increment of pituitary deiodination. As described for liver, higher skeletal muscle D1 activity suggests a hyperthyroid status. Our data broaden the knowledge about the adaptive changes to malnutrition during lactation and reinforce the concept of neonatal programming of the thyroid function.

Key Words: protein-restricted diet • lactation • programming • deiodinase • TSH • TRH

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