To investigate whether MSM may provide preventive effects on PAH, an experimental study was conducted examining the activity of antioxidative enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in the serum samples from rats with MCT-induced PAH subjected to pretreatment. The gene discussed is CAT; the disease is pulmonary arterial hypertension.