TEMPERATURE-MODULATED INCIDENCE OF AFLATOXIN B1-INITIATED LIVER-CANCER IN RAINBOW-TROUT

Rainbow trout (initial weight of 4 or 5 g) were acclimated at a cool, 11.0 degrees C (C), a warm, 18.0 degrees C (W), or an intermediate tem perature 14.5 degrees C (I) for 1 month. There was a slight difference in hepatic microsomal content of one of six cytochrome P450 isozymes between acclimation groups. Monounsaturated fatty acids in hepatic pho sphotidylethanolamine but not phosphotidylcholine increased at lower a cclimation temperatures. Saturated fatty acid content decreased with t emperature for both phospholipid classes. Fish were exposed to 0.08-0. 12 ppm waterborne aflatoxin B1 (AFB1) for 30 min at respective acclima tion temperatures or after acute temperature shifts (24 hr) and reared for 9 months at C, I, or W. With exposure concentrations which delive red equivalent target organ doses, trout acclimated, exposed, and rear ed at C, I, or W had liver tumor incidences of 4, 35, and 61%, respect ively. The average number of tumors per liver increased from 1.25-1.34 at C to 2.46-2.66 at W. There were no temperature-dependent differenc es in tumor diameter. When C- and W-acclimated fish were AFB1 exposed and reared at I, tumor incidence was 12.5% for W-I-shifted fish and 26 .5% for C-I-shifted fish. This was consistent with previous work which demonstrated acute downward temperature shift reduced [H-3]AFB1 adduc tion to hepatic DNA. Tumor incidence and multiplicity data suggested m anipulation of temperature permitted selective modulation of cancer in itiation and promotion in rainbow trout. (C) 1995 Society of Toxicolog y.