Thermal acclimatization of hepatic polysubstrate monooxygenase and UDP-glucuronosyltransferase of mature rainbow trout (Salmo gairdneri).

The thermal acclimatization of hepatic cytochrome P-450-dependent polysubstrate monooxygenase (PSMO) and UDP-glucuronosyltransferase of mature rainbow trout (Salmo gairdneri) was studied. The results indicate that the PSMO system, 7-ethoxycoumarin and benzo(a)pyrene as substrates, shows almost ideal acclimatization pattern in autumn during water cooling. The enzyme activities were identical if measurements were carried out at acclimatization (=environmental) temperatures which were 20 degrees C in August and 5 degrees C in November. If a constant incubation temperature (18 degrees C) was used, the PSMO activities were significantly higher in cold (5 degrees C)-acclimatized fish. The acclimatization process could be seen both in specific and total activities. The content of cytochrome P-450 remains at constant level from August to November. In early summer during water warming the PSMO activities increased considerably in both sexes in all incubation conditions. The specific and total UDP-glucuronosyltransferase activities were significantly higher in warm-acclimatized fish both in the autumn and in the spring if the activities were measured at environmental temperature. No differences could be detected if the measurements were carried out at constant experimental temperature (18 degrees C).