Involvement of nitric oxide and hyperbaric oxygen in the pathogenesis of cyclophosphamide induced hemorrhagic cystitis in rats

Purpose: We evaluated the relationship between nitric oxide and hyperbaric oxygenation in the pathogenesis and treatment of cyclophosphamide induced hemorrhagic cystitis in rats. Materials and Methods: Cyclophosphamide (100 mg/kg) was injected in male Sprague-Dawley rats for cystitis induction. Animals were treated before and the day after cyclophosphamide injection with 100 mg/kg of the nitric oxide substrate L-arginine, 20 mg/kg of the nonselective nitric oxide synthase inhibitor L-N-G-nitroarginine methyl ester and 20 mg/kg of the selective inducible nitric oxide synthase inhibitor S-methylisothiourea. Animals were exposed to hyperbaric oxygen (2.8 atmospheres absolute for 90 minutes twice daily) with or without the administration of L-arginine and nitric oxide synthase inhibitors. Results: Cyclophosphamide injection resulted in severe cystitis. S-methylisothiourea produced marked inhibition of cyclophosphamide induced bladder tissue damage. L-arginine and L-N-G-nitroarginine methyl ester failed to a show meaningful protective effect. Hyperbaric oxygen protected the bladder only against ulceration. Moreover, hyperbaric oxygen did not contribute to the protective effects of L-arginine, L-N-G-nitroarginine methyl ester or S-methylisothiourea. Conclusions: Nitric oxide produced by inducible nitric oxide synthase is an important mediator in the pathogenesis of cyclophosphamide induced cystitis. Hyperbaric oxygen has a beneficial effect on repairing bladder damage rather than on bladder protection.