AJP - Endocrinology and Metabolism, Vol 267, Issue 6 E983-E989, Copyright © 1994 by American Physiological Society
Effects of thyroid hormone deiodination on regulation of thyroid axis in undernourished rats
A. M. Pascual-Leone, C. Alaez, R. Calvo, M. A. Martin and M. J. Obregon
Instituto de Bioquimica [Centro Mixto Consejo Superior de Investigaciones Cientificas (CSIC)-Universidad Complutense de Madrid], Facultad de Farmacia, Ciudad Universitaria, Spain.
The possible influence of hypothalamic and pituitary 5'-deiodinase II
(5'-D-II) activity and 3,5,3'-triiodothyronine (T3) content on the
modulation of thyroid-stimulating hormone (TSH) synthesis was studied. 1)
Alterations in 5'-D-II activity and hypothalamic and pituitary T3 content
produced by undernutrition were observed in fetal (21 days) and neonatal
rats vs. controls. 2) After thyroidectomy, plasma TSH increased in both
populations, undernourished and control, but pituitary TSH increased only
in the former and not in the latter. The results obtained by giving small
doses of thyroxine (T4; 0.5 micrograms/100 g body wt) to intact and
thyroidectomized rats suggest a lower inhibitory effect by T4 on the
pituitary in undernourished than in control rats. Although hypothalamic and
pituitary 5'-D-II activity increased in both groups after thyroidectomy,
the percentage increase was lower in undernourished vs. control rats,
resulting in lower overall T3 content in tissues from undernourished
animals. These studies on thyroid axis regulation show the in vivo
regulation of TSH synthesis by hypothalamic and pituitary 5'-D-II activity
and T3 content.
