CYP1B1 and pulmonary arterial hypertension: Interestingly, the assumed differences between P90-9NA, P90-BaP and AS-PAH are also reflected in the level of induction of Cyp1a1 and Cyp1b1 mRNA, in that P90-9NA resulted in the least induction, followed by P90-BaP, with the strongest induction by AS-PAH.