Expression of nitric oxide synthase in bladder smooth muscle cells: regulation by cytokines and L-arginine.

PURPOSE: The expression and regulation of the different isoforms of nitric oxide synthase (NOS) in bladder smooth muscle cells are controversial and to our knowledge have not yet been studied systematically. Therefore, the expression and regulation of NOS were studied in rat bladder smooth muscle cells after stimulation with cytokines, lipopolysaccharide and L-arginine. MATERIALS AND METHODS: Primary cell cultures were prepared from rat bladders. The expression of NOS mRNA was examined by reverse transcriptase-polymerase chain reaction and inducible NOS (iNOS) protein expression was studied by Western blot analysis and immunohistochemistry. Nitrite accumulation in the culture medium was determined by the Griess assay. The expression of iNOS was also studied immunohistochemically in whole bladder strips stimulated by cytokines. RESULTS: NOS mRNA expression was not detected in unstimulated cells. Stimulating bladder smooth muscle cells with a cytokine mixture of interferon-gamma, tumor necrosis factor-alpha and interleukin-1beta induced iNOS mRNA and protein expression. The combination of interleukin-1beta plus tumor necrosis factor-alpha appeared to be crucial for iNOS induction in bladder smooth muscle cells. Exposing bladder smooth muscle cells to lipopolysaccharide did not induce iNOS. Adding L-arginine increased nitrite accumulation in cytokine mixture stimulated bladder smooth muscle cells, while iNOS positive cells were detected in the smooth muscle layer of cytokine mixture stimulated bladder strips. CONCLUSIONS: NOS was not detected in unstimulated bladder smooth muscle cells. However, bladder smooth muscle has the potential to express iNOS when exposed to cytokines known to be produced during urinary tract infection.

Escherichia coli-induced inducible nitric oxide synthase and cyclooxygenase expression in the mouse bladder and kidney.

BACKGROUND: The host response to urinary tract infection includes the production of different inflammatory mediators. We investigated the cellular localization and time course of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) expression in the mouse bladder and kidney after bacterial infection. METHODS: Experimental urinary tract infection in mice was established by intravesical inoculation of a clinical uropathogen Escherichia coli (E. coli) AD 110. Urine was collected at 6-, 12-, 24-, and 72-hours postinstillation, and the nitrite concentration was determined. The induction of iNOS and COX-2 was studied by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Nitrite levels in the urine had increased threefold at 6 and 12 hours postbacterial instillation. Bladders from mice instilled with AD 110, but not with phosphate-buffered saline, showed a large number of iNOS-- and COX-2--expressing inflammatory cells. The inflammatory cell activation peaked at 6 and 12 hours postinstillation and had vanished by 72 hours. iNOS expression was detected in some urothelial cells after 24 and 72 hours, but COX-2 expression was not detected. In the kidney, infection activated an iNOS and COX-2 response, as shown by immunoreactivity in inflammatory cells at all time points. A strong epithelial iNOS response was observed in the renal pelvis at 12, 24, and 72 hours postinstillation, but COX-2 was not detected. Enhanced tissue expression of iNOS and COX-2 after bacterial instillation was also demonstrated by RT-PCR. CONCLUSIONS: E. coli AD 110 induced expression of iNOS and COX-2 in the urinary tract. Inflammatory cells expressed both iNOS-and COX-2, but epithelial cells expressed only iNOS and with a later onset than in the inflammatory cells. This suggests that the epithelial iNOS response is not caused by direct bacterial activation, but more likely is by mediators involved in the inflammatory response.

Morphological and biochemical investigation of nitric oxide synthase and related enzymes in the rat and pig urothelium.

We investigated the enzymes involved in the NADPH-diaphorase (d) reaction in the rat and pig bladder urothelium. The urothelial cell layer displayed intense and uniform NADPH-d activity. Preincubation with the flavoprotein inhibitor diphenyleneiodionium chloride (DPI) and the alkaline phosphatase inhibitor levamisole concentration-dependently decreased the urothelial NADPH-d activity. Immunoreactivities to neuronal (n), endothelial (e), or inducible (i) nitric oxide synthase (NOS) were not detected in rat or pig urothelial cells. In rats, the urothelium was uniformly immunoreactive for NADPH cytochrome P450 reductase, whereas the pig urothelium displayed inconsistent labeling. In lipopolysaccharide (LPS)-treated rats, the bladder urothelium showed positive iNOS immunoreactivity. The iNOS labeling was found predominantly in cells located in the basal layer of the urothelium. In the pig bladder mucosa, a Ca2+-dependent NOS activity was evident in cytosolic and particulate fractions that was quantitatively comparable to the NOS activity found in the smooth muscle. In ultrastructural studies of urothelial cells, NADPH-d reaction products were found predominantly on membranes of the nuclear envelope, endoplasmatic reticulum and mitochondria. In conclusion, NADPH-d staining of the urothelium cannot be taken as an indicator for the presence of constitutively expressed NOS. Activity of alkaline phosphatase and cytochrome P450 reductase may account for part of the NADPH-d reaction in urothelial cells. However, LPS treatment of rats caused expression of iNOS in urothelial cells.