DIFFERENTIAL INDUCTION OF 2 2,3,7,8-TETRACHLORODIBENZO-PARA-DIOXIN-INDUCIBLE FORMS OF CYTOCHROME-P-450 IN EXTRAHEPATIC VERSUS HEPATIC TISSUES

  • 1 January 1984
    • journal article
    • research article
    • Vol. 25  (1) , 185-191
Abstract
The induction of 2 isozymes of cytochrome P-450, P-448HCB and P-448MC, by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in hepatic and a number of extrahepatic tisues of male rats was examined. These isozymes were quantitated by radioimmunoassay (RIA). TCDD induces both forms of cytochrome P-448 makredly in liver. In extrahepatic tissues, TCDD induces cytochrome P-448MC but not cytochrome P-448HCB. Induction of cytochrome P-448MC is greatest in liver > kidney > lung > intestine > spleen > testes > brain (no significant increase). The results in liver, kidney and lung were confirmed by a technique that depends on both electrophoretic mobility and immunological characteristics (sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by transfer to nitrocellulose paper and immunostaining of the protein). Cytochrome P-448HCB is a minor constitutive form in livers of control male rats (5% of the total cytochrome P-450). Cytochrome P-448MC is below the level of detection in control livers using the immunostaining technique (< 0.6% by RIA). Induction of cytochrome P-450 isozymes by TCDD is evidently tissue-dependent in the rat. The response of extrahepatic tissues to TCDD is more limited than that of liver.

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