CYP1B1 and chronic kidney disease: To explore if the accumulation of Tryp-derived uremic metabolites results in AHR activation in skeletal muscle, we employed quantitative PCR (qPCR) to measure the mRNA expression of the AHR and downstream cytochrome P450 genes, CYP1A1 and CYP1B1, in gastrocnemius muscle from participants with and without CKD.