© 1990 Oxford University Press
research-article |
Biliary Excretion Appears Rate Limiting for Hepatic Elimination of Benzo[a]pyrene by Temperature-Acclimated Rainbow Trout
Oak Creek Laboratory of Biology, Department of Fisheries and Wildlife, Oregon State University Corvallis, Oregon 97331-3803
Received October 11, 1989; accepted May 9, 1990
Biliary Excretion Appears Rate Limiting for Hepatic Elimination Of Benzo[a]pyrene by Temperature-Acclimated Rainbow Trout. CURTIS, L. R., FREDERICKSON, L. K., AND CARPENTER, H. M. (1990) Fundam. Appl. Toxicol. 15, 420–428. 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°C for 4 weeks and then ip injected with 10 µmol [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 extract-able [3H] or [14C]BP tissue concentrations in 10 and 18°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°C than at 10°C. Therefore, warmer temperature stimulated biliary excretion without a marked effect on in vivo BP metabolism. In the second regimen, 10 and 18°C-accli-matedfish were shifted to 14°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°C. However, the biliary concentration of [14C]BP not extracted by ethyl acetate was significantly higher in bile from 10°C-acclimated fish than from 18°C-acclimated fish when both groups were exposed at 14°C. In this case, in vivo BP metabolism was altered without coincident effects on biliary excretion. Aryl hydrocarbon hydroxylase assayed at 14°C was about threefold higher in hepatic microsomes from 10°C-acclimated fish than from 18°C-acclimated fish. Exposure temperature selectively modulated BP metabolism and biliary excretion in temperature-acclimated rainbow trout.