Biliary excretion appears rate limiting for hepatic elimination of benzo[a]pyrene by temperature-acclimated rainbow...

Previous work demonstrated that mixed function oxidase activities of hepatic microsomes from cold- and warm-acclimated rainbow trout were similar when assayed at temperatures to which fish were acclimated. This "ideal temperature compensation" was partially explained by constitutive differences in microsomes. In the work reported here, rainbow trout were acclimated at 10 or 18 degrees C for 4 weeks and then ip injected with 10 mumol [3H] or [14C]benzo[a]pyrene (BP)/kg in one of two temperature regimens. First, fish were acclimated and exposed at the same temperature and killed after 4, 24, or 48 hr. Concentrations of [3H]BP equivalents in liver, bile, and fat but not in plasma, muscle, intestine, gill, or kidney increased with time. There were no differences in hexane or ethyl acetate extractable [3H] or [14C]BP tissue concentrations in 10 and 18 degrees C-acclimated fish exposed at their acclimation temperatures. At 24 hr after injection, biliary excretion of [3H]BP equivalents was about twofold higher at 18 degrees C than at 10 degrees C. Therefore, warmer temperature stimulated biliary excretion without a marked effect on in vivo BP metabolism. In the second regimen, 10 and 18 degrees C-acclimated fish were shifted to 14 degrees C, injected with [3H] or [14C]BP 1 hr later, and killed after an additional 24 hr. There were no differences in tissue concentrations of total [3H]BP equivalents between acclimation groups at 14 degrees C. However, the biliary concentration of [14C]BP not extracted by ethyl acetate was significantly higher in bile from 10 degrees C-acclimated fish than from 18 degrees C-acclimated fish when both groups were exposed at 14 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)