Predominant role of peripheral catecholamines in the stress-induced modulation of CYP1A2 inducibility by benzo(α)pyrene
Johnson, Elizabeth O.
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The potential involvement of catecholamines and in particular of α2-adrenoceptor-related signalling pathways, in the regulation of drug-metabolizing enzymes by stress was investigated in Wistar rats after exposure to the environmental pollutant benzo(α)pyrene. For this purpose, total cytochrome P450 content, the CYP1A2 mRNA levels, 7-methoxyresorufin-O- dealkylase (MROD), 7-pentoxyresorufin-O-dealkylase (PROD) and p-nitrophenol hydroxylase activity levels were determined in the livers of rats exposed to repeated restraint stress after treatment with benzo(α)pyrene coupled with pharmacological manipulations of peripheral and/or central catecholamines and α2-adrenoceptors. The data show that stress is a significant factor in the regulation of CYP1A2 induction and that catecholamines play a central role in the stress-mediated modulation of hepatic CYP1A2 inducibility by benzo(α)pyrene. The up-regulating effect of stress on benzo(α)pyrene-induced CYP1A2 gene expression was eliminated after a generalized catecholamine depletion with reserpine. Similarly, in a state where only peripheral catecholamines were depleted and central catecholamines remained intact after guanethidine administration, the up-regulating effect of stress was eliminated. It is apparent that stress up-regulates the induction of CYP1A2 by benzo(α)pyrene mainly via peripheral catecholamines, while central catecholamines hold a minor role in the regulation. Pharmacological manipulations of α2-adrenoceptors appear to interfere with the effect of stress on the regulation of CYP1A2 inducibility. Either blockade or stimulation of α2-adrenoceptors with atipamezole and dexmedetomidine respectively, eliminated the up-regulating effect of stress on CYP1A2 benzo(α)pyrene-induced expression, while it enhanced MROD activity. In contrast, stress and pharmacological manipulations of catecholamines and α2-adrenoceptors did not affect total P450 content, the CYP2B1/2-dependent PROD and the CYP2E1-dependent p-nitrophenol hydroxylase activities. In conclusion, stress is a significant factor in the regulation of the CYP1A2 inducibility by benzo(α)pyrene, which in turn is involved in the metabolism of a large spectrum of toxicants, drugs and carcinogenic agents. Although the mechanism underlying the stress effect on CYP1A2 induction has not been clearly elucidated, it appears that peripheral catecholamines hold a predominant role, while central catecholamines and in particular, central noradrenergic pathways hold a minor role.