COMPARATIVE DIAZINON TOXICITY IN GUPPY AND ZEBRA FISH - DIFFERENT ROLE OF OXIDATIVE-METABOLISM

Guppies pretreated with 1.1 mumol/L diazinon (0.5 times the LC50 with the guppy) for 7 d were less susceptible to the toxicity of the compou nd. The LC50 in these fish was about five times higher than that in no npretreated animals. The lethal body burden and the slope of the conce ntration-response curve of diazinon in pretreated guppies were similar to those in zebra fish. The 7-d pretreatment of zebra fish with 12 mu mol/L diazinon (0.5 times the LC50 with the zebra fish) did not affect the susceptibility of this species to diazinon. The pretreatment of g uppies resulted in a strong inhibition of the formation of diazoxon an d pyrimidinol during incubations of diazinon with the hepatic postmito chondrial supernatant. During exposure of guppies and zebra fish to di azinon, the tissue concentration of the metabolite, pyrimidinol, initi ally increased and then declined to very low levels. In the guppy, con currently with the decrease of the metabolite concentration, the paren t compound began accumulating again after a temporary steady state. Th e hypotheses of this paper are that the toxicity of diazinon in the gu ppy is due to its metabolism to a highly toxic metabolite, likely diaz oxon; and in zebra fish or pretreated guppies having low rates of diaz inon metabolism toxicity is due to the accumulation of the parent comp ound.