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Changes in thyroid status have a major effect on the GH/insulin-like growth factor (IGF) axis. The majority of IGF in the circulation is bound to specific IGF-binding proteins (IGFBPs) of which six have been cloned and sequenced. We have studied changes in hepatic gene expression of IGFBP-1, -2 and -3, in male Wistar rats rendered hyperthyroid (thyroxine, 200 µg/kg per day) or hypothyroid (propylthiouracil, 0·1% daily). Littermates of the same age were used as controls (n=6 in each group). Thyroxine was measured by radioimmunoassay, and hepatic IGFBP-1, -2 and -3 mRNA levels by Northern blot analysis using specific rat cDNA probes with a 28S ribosomal probe as a loading control. Mean± S.E.M. thyroxine levels were 247·0±44·5 (hyperthyroid group), <9·0 (hypothyroid group) and 76·0 ± 4·5 nmol/l (control group). IGFBP-1 and -2 mRNA levels in the hypothyroid animals compared with the controls were significantly increased, but similar levels of expression were found in thyrotoxic and control rats. IGFBP-3 mRNA levels in hypothyroid animals were decreased, and increased in thyrotoxic animals. Thus, in the adult rat, hypothyroidism is associated with increased hepatic IGFBP-1 and -2 gene expression, but decreased IGFBP-3 gene expression, while in thyrotoxicosis there are normal IGFBP-1 and -2 mRNA levels but increased IGFBP-3 gene expression. These results suggest that there is specific and different transcriptional regulation for IGFBP-1, -2 and -3 in hypoand hyperthyroid rats.

Journal of Endocrinology (1994) 140, 251–255

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				H. C. Freake, K. E. Govoni, K. Guda, C. Huang, and S. A. Zinn Actions and Interactions of Thyroid Hormone and Zinc Status in Growing Rats J. Nutr., April 1, 2001; 131(4): 1135 - 1141. [Abstract] [Full Text]