Abstract
Polycyclic hydrocarbons induce the microsomal enzyme aryl hydrocarbon (benzo[a]pyrene) hydroxylase in the livers of intact rats and in hamster embryo cells. In vivo, methylcholanthrene causes an increased incorporation of precursors into nuclear RNA and an increased RNA polymerase activity in hepatic nuclei. Gel electrophoresis of RNA synthesized in vitro by isolated nuclei has shown that the synthesis of all sizes of RNA is enhanced by the methylcholanthrene treatment in vivo. Hypophysectomized or adrenalectomized rats previously treated with hydrocarbons fail to exhibit an increase in RNA polymerase activity, although they manifest an increase in the level of aryl hydrocarbon hydroxylase.
Double-labeling techniques and acrylamide gel electrophoresis showed no detectable change in the pattern of RNA synthesized during enzyme induction in cell culture. The latter studies and those carried out in vivo with adrenalectomized and hypophysectomized rats suggest that the methylcholanthrene-induced gross changes in liver nuclear RNA metabolism in vivo are not requirements for microsomal enzyme induction, and that the induction-specific RNA synthesis, indicated as a requirement by our other studies, is of small magnitude.
- Copyright ©, 1972, by Academic Press, Inc.
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