Cultured mouse embryos metabolize benzo[a]pyrene during early gestation: genetic differences detectable by sister chromatid exchange.

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Abstract
Mouse embryos explanted at 7 1/2 or 8 1/2 days of gestation were cultured in medium containing benzo[a]pyrene [on embryotoxin] and supplemented with 5-bromodeoxyuridine to allow detection of sister chromatid exchanges. The murine Ah locus regulates the inducible metabolism of polycyclic hydrocarbons such as benzo[a]pyrene. A high frequency of sister chromatid exchange was induced by benzo[a]pyrene in embryos from 3 Ah-responsive inbred strains (BALB/cDub, C3H/AnfCum and C57BL/6N); there was little or no increase in 2 Ah-nonresponsive inbred strains (AKR/J and DBA/2J). Benzo[a]pyrene also induced sister chromatid exchanges in the Ah-responsive recombinant inbred line B6NXAKN-12 but not in the Ah-nonresponsive recombinant inbred line B6NXAKN-3. Sister chromatid exchange in cultured Ah-responsive mouse embryos was thus shown to be a sensitive assay. Genetically responsive mouse embryos (early postimplantation stage) possess the subcellular processes necessary for induction of enzymes that metabolize benzo[a]pyrene to its chemically active form(s). Ah regulatory gene product (a cytosolic receptor) and the structural gene product (inducible cytochrome P1-450) therefore appear to be functional at an early embryonic age. This metabolic capacity may play an important role in the damage to embryonic cells by polycyclic hydrocarbons.