The adrenal steroid products, glucocorticoids, appear to play an important role in the expression of hepatic cytochrome P-450 dependent monooxygenases and other enzymes involved in metabolism of foreign compounds. These proteins are known to be involved in the metabolic activation of chemicals to form chemically-reactive intermediates capable of altering growth and development. We have observed a synergism in the induction of some hepatic enzyme activities by polycyclic aromatic hydrocarbons (PAH) in the presence of glucocorticoids, including dexamethasone. The effects of glucocorticoids on the expression of hepatic monooxygenases and other enzymes involved in foreign compound metabolism in culture will be measured by enzyme assay, by immunoblotting techniques with antibodies to the hepatic enzymes, and by measurement of the levels of mRNA specific for these enzymes with in vitro translation and Northern analyses. A second specific aim will involve use of adrenalectomized animals to ascertain whether lack of adrenal steroids diminishes the induction of these enzymes by PAH in vivo. Other inducing agents will be tested for glucocorticoid synergism: barbiturates, catatoxic steroids, isosafrole, clofibrate, and ethanol. The biochemical mechanism of the synergistic induction will be studied using modern biochemical techniques. The interaction between these two organs will also be tested in vivo to establish the role of adrenal steroids on monooxygenase- mediated toxicity in fetal, neonatal, and adult tissue. DNA damage and the extent of inducibility of these enzymes as a function of age (gestational and neonatal) will be determined. The information gained will aid in understanding the general processes involved in the maintenance of the hepatic xenobiotic metabolizing enzymes in vivo as a function of ontogenic development. The project will also assess the effects of glucocorticoids alone on the precocious induction of these same enzyme systems in cell culture. The various enzymes of interest will be quantitated by enzyme assay, immunoblotting techniques and by quantitating the levels of mRNA with specific cDNA probes. These experiments should provide an understanding of the mechanism of precocious induction by these adrenal steroids in cell culture and possibly in vivo.
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