11 beta-hydroxysteroid dehydrogenase bioactivity is increased in the colonbut not kidneys of rats given supplementary thyroxine.

The aim of this study was to investigate the effect of altered thyroid stat us on 11 beta -hydroxysteroid dehydrogenase type 1 (11 beta -HSD type 1) an d type 2 (11 beta -HSD type 2) bioactivity in rat kidney and colon. Male Sp rague-Dawley rats (250g) were treated with either L-thyroxine (T4) or propy lthiouracil (PTU) for 4 weeks. Blood were then analysed for serum thyroxine , sodium (Na+) and potassium (K-). The kidneys and colon were assayed for 1 1 beta -HSD type 1 and 11 beta -HSD type 2 bioactivity. In T4 treated rats the serum thyroxine was significantly elevated (p < 0.05) whilst PTU decrea sed serum thyroxine significantly (p < 0.001) compared to controls. Serum N a+ and K+ were within normal limits. There were no significant changes in 1 1 beta -HSD type 1 bioactivity in both treatment groups compared to control s. However, the 11 beta -HSD type 2 bioactivity in rats given thyroxine was significantly higher in the colon (p < 0.003) compared to controls. We con clude that altered thyroid status had no effect on 11<beta>-HSD type 1 bioa ctivity but 11 beta -HSD type 2 bioactivity was elevated in the colon of ra ts given supplementary thyroxine.