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Horm Metab Res 2001; 33(9): 532-535
DOI: 10.1055/s-2001-17211
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© Georg Thieme Verlag Stuttgart · New York

Sex Steroids Modulate Rat Anterior Pituitary and Liver Iodothyronine Deiodinase Activities

P. C. Lisbôa, F. H. Curty, R. M. Moreira, K. J. Oliveira, C. C. Pazos-Moura
  • Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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Publication History

Publication Date:
17 September 2001 (online)

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In this study, we investigated the sex hormone regulation of 5’-iodothyronine deiodinase activity, which is responsible for enzymatic conversion of thyroxine into the bioactive form, triiodothyronine. Pituitary homogenates and liver microsomes from: 1) ovariectomized rats injected with 17-β-estradiol benzoate and/or progesterone (0.7 and 250 µg/100 g body weight, respectively, subcutaneously, over 10 days); 2) male castrated rats treated or not with 0.4 mg/100 g body weight testosterone propionate, intramuscular, over 7 days, were assayed for type 1 and type 2 deiodinase activity in the pituitary. Enzyme activities were measured by release of 125I from deiodination of 125I reverse triiodothyronine under varying assay conditions. Estrogen stimulated anterior pituitary and liver type 1 deiodinase activity in ovariectomized rats (45 and 30 %, p < 0.05). Progesterone inhibited the liver enzyme (40 %, p < 0.05), and had no effect on the pituitary, but in both tissues, blocked estrogen stimulatory effect on type 1 deiodinase. In males, testosterone normalized the reduced liver type 1 deiodinase of castrated rats. However, in the pituitary, castration increased (50 %) type 1 deiodinase independent of testosterone treatment, suggesting the existence of a inhibitory testicular regulator of pituitary type 1 enzyme. Treatments did not alter pituitary type 2 deiodinase activity. In conclusion, gonads and sex steroids differentially modulate type 1 deiodinase activity in rat pituitary and liver.

Key words:

5’-Deiodinase - Castration - Estradiol - Progesterone - Testosterone

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C. C. Pazos-Moura

Laboratório de Endocrinologia Molecular
Instituto de Biofisica Carlos Chagas Filho
Universidade Federal do Rio de Janeiro

CCS, Bloco G, Ilha do Fundão
Rio de Janeiro
Brazil


Fax: + 55 (21) 280-8193

Email: cpazosm@ibccf.biof.ufrj.br