We have investigated the effect of benzo[a]pyrene (B[a]P). a carcinogen of tobacco smoke and an agonist for the aryl hydrocarbon receptor (AHR), on hypoxia-induced angiogenesis. Ischemia was induced by femoral artery ligation in wild-type and ASR-null mice, and the animals were subjected to oral administration of B[a]P (125 mg/kg) once a week. Exposure to B[a]P up-regulated the expression of metallothionein in the ischemic hindlimb and markedly inhibited ischemia-induced angiogenesis in wild-type mice. The amounts of interleukin-6 and of vascular endothelial growth factor (VEGF) mRNA in the ischemic hindlimb of wild-type mice were reduced by exposure to B[a]P. These various effects of B[a]P were markedly attenuated in ASR-null mice. Our observations suggest that the loss of the inhibitory effect of B[a]P on ischemia-induced angiogenesis apparent in ASR-null mice may be attributable to maintenance of interleukin-6 expression and consequent promotion of angiogenesis through up-regulation of VEGF expression. (C) 2009 Elsevier Inc. All rights reserved.