Immunohistochemical detection of apoptosis, proliferation and inducible nitric oxide synthase in rat urothelium damaged by cyclophosphamide treatment


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The present study was conducted to investigate cell death, proliferation and inducible nitric oxide synthase (iNOS) immunoreactivity in rat urothelium within 24 h after a single intraperitoneal dose of cyclophosphamide (CP). Necrotic cells were identified predominantly in the superficial cell layer from 1 h until 6 h after CP injection, most of them desquamating from the urothelium into the lumen of the urinary bladder. Active caspase-3 immunohistochemistry revealed apoptotic cells from 12 h until 24 h after CP injection. The apoptotic index reached a peak at 18 h and then rapidly dropped. Simultaneously with the decrease of apoptosis, the proliferation index increased from 18 h until 24 h after CP treatment. Immunoreaction to iNOS was first detected at 6 h in basal and intermediate cells. Later, iNOS immunoreactivity became stronger and was present in all cell layers. Our results suggest that the destruction of rat urothelium during 24 h after CP administration is due not only to necrosis, but also to apoptosis. The first 6 h are characterised by necrotic changes and no iNOS immunoreactivity. Thereafter, apoptosis and iNOS immunoreactivity are observed within the damaged urothelium. At 24 h after CP injection, iNOS immunoreactivity is still present, but proliferation prevails over cell death, enabling the urothelium to start regeneration.