Metabolism of the carcinogen benzo[a]pyrene by the intestine of fish

Studies were undertaken to identify factors influencing the metabolism of benzo[a]pyrene (BP) by the mixed function oxygenase (MFO) system of fish intestine. Exposure of spot (Leiostomus xanthurus) to dietary PAH resulted in rapid and large increases in intestinal microsomal MFO activity but had no effect on hepatic MFO activity. MFO activity was highest in the pyloric caeca and proximal half of the intestine. Starvation resulted in no detectable MFO activity. The increase in intestinal MFO activity following dietary PAH exposure resulted from induction of specific forms(s) of intestinal cytochrome P-450 isozymes involved in PAH metabolism. A major form of intestinal cytochrome P-450 induced in spot was immunologically similar to the major PAH-inducible form in fish liver. To determine the efficiency of BP metabolism by the intestine of live fish, the portal veins of toadfish (Opsanus tau) were cannulated following administration of radiolabeled BP to the intestinal lumen. Pre-exposure of fish to dietary PAH enhanced the efficiency of intestinal BP metabolism