Abstract
The aim of this study was to investigate the differences between rats and hamsters,
Two of the most widely used experimental animals, with respect to the effects of microsomal
membrane solubilization on the inhibition of liver 11β-hydroxysteroid dehydrogenase
(11β-HSDI) enzyme by bile acids. Liver microsome fractions were prepared, and the
11β-HSDI enzymatic activity was measured using cortisone as a substrate. The substrate
and various concentrations of bile acids were added to the assay mixtures. After incubation,
the products were extracted and analyzed using high-performance liquid chromatography.
To investigate the effect of detergent on the inhibitory effects of bile acids, we
conducted inhibition tests using Triton X-100-solubilized animal liver microsomes.
When solubilized microsomes were used, all bile acids inhibited 11β-HSDI from rats
and hamsters to various degrees. 7α-Hydroxycholanoic acids (cholic acid and chenodeoxycholic
acid) in particular had strong inhibitory activities. In hamsters, 7β-hydroxycholanoic
acid (ursodeoxycholic acid) was the strongest inhibitor among the bile acids tested,
although its effect was not very strong. When nonsolubilized microsomes were used,
deoxycholic acid did not inhibit but rather enhanced the enzymatic activity in both
animals. Microsomal content of cholesterol and phospholipids are significantly different
between rats and hamsters. Species differences in bile acid inhibition of nonsolubilized
microsomes might be reflected not only by structural difference of bile acids, which
affect membrane solubilization and enzyme activity directly, but also species difference
in microsomal membrane lipid content.
Key words
microsomes - solubilization - 11β-hydroxysteroid dehydrogenase - bile acid - rat
- hamster
