GROWTH-HORMONE EFFECT ON XENOBIOTIC-METABOLIZING ACTIVITIES OF RAINBOW-TROUT

In recent years several studies reported the regulation by growth horm one (GH) of the expression of a variety of P450 forms in mammals. Howe ver the effect of GH on the xenobiotic-metabolizing enzymes of fish ar e still unknown. The aim of this work was to investigate the effects o f ovine GH- growth hormone known to be efficient in trout-on the cytoc hrome P450 level and on aryl hydrocarbon hydroxylase, aminopyrine-N-de methylase, glucuronyl transferase and glutathione transferase activiti es in trout. The GH-implanted trout (n = 50) each received a single ch olesterol pellet containing ovine GH and were compared to control anim als (n = 50) receiving a single cholesterol pellet without GH. After 1 5 days fish were killed and the liver and gills were excised for the m easurement of xenobiotic-metabolizing enzyme activities. GH treatment significantly decreased the level of hepatic cytochrome P450 and the a ctivities of cytochrome P450 dependent monooxygenases. In contrast, no significant effect of the treatment was observed on the glutathione t ransferase and UDP-glucuronyl transferase activities. Moreover, GH tre atment had no effect on branchial phase I and phase II enzyme activiti es. This study provides evidence that GH level significantly affects t he expression of several members of the hepatic cytochrome P450 family in trout.