11β-Hydroxysteroid dehydrogenase bioactivity is increased in the colon but not kidneys of rats given supplementary thyroxine.

Summary:

The aim of this study was to investigate the effect of altered thyroid status on 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD type 1) and type 2 (11β-HSD type 2) bioactivity in rat kidney and colon. Male Sprague-Dawley rats (250g) were treated with either L-thyroxine (T4) or propylthiouracil (PTU) for 4 weeks. Blood were then analysed for serum thyroxine, sodium (Na⁺) and potassium (K⁺). The kidneys and colon were assayed for 11β-HSD type 1 and 11β-HSD type 2 bioactivity. In T4 treated rats the serum thyroxine was significantly elevated (p < 0.05) whilst PTU decreased serum thyroxine significantly (p < 0.001) compared to controls. Serum Na⁺ and K⁺ were within normal limits. There were no significant changes in 11β-HSD type 1 bioactivity in both treatment groups compared to controls. However, the 11β-HSD type 2 bioactivity in rats given thyroxine was significantly higher in the colon (p < 0.003) compared to controls. We conclude that altered thyroid status had no effect on 11β-HSD type 1 bioactivity but 11β-HSD type 2 bioactivity was elevated in the colon of rats given supplementary thyroxine.

Key words:

Thyroxine - propylthiouracil - 11β-hydroxysteroid - dehydrogenase - serum sodium - serum potassium

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