Bladder disorders such as overactive bladders affect millions of people worldwide but their pathogenesis is poorly understood. Recently, the role of the urothelium in bladder function and pathology has generated intense interest, in particular its regulation by inflammatory mediators. Angiotensin II is trophic factor and inflammatory mediator, and is involved in bladder obstruction and hypertrophy. However, its role in urothelial function has never been studied. The aim of this study was to identify the presence and localisation of angiotensin receptor AT1 within the bladder wall and to elucidate the role of angiotensin II in urothelial and bladder function. Guinea-pigs (male Dunkin-Hartley 450-550g) were euthanized with schedule-1 procedure. Immuno-fluorescence was performed on frozen bladder sections with an AT1 primary antibody and an Alexa-586-conugated secondary antibody. Mucosa-intact smooth muscle strips and mucosal strips were isolated from the urinary bladders. The preparations were superfused in a HEPES-buffered Tyrode’s solution for functional measurement. The isometric tension was recorded with a tension-transducer via a bridge-amplifier. The superfusate adjacent to the tissue strip was sampled and ATP release from the tissue was measured using a luciferin-luciferase assay.Application of angiotensin II (200nM and 1µM) significantly increased ATP release from the bladder mucosa (pmoles/g/min, median (25%-75% range); control: 166 (101- 357) vs. 200nM angiotensin II: 221 (197 – 1256); n=9, p<0.05; control: 140 (44-360) vs. 1µM angiotensin II: 208 (89-641); n=14; p<0.05, Wilcoxon signed rank test). This effect was largely inhibited by AT1 antagonist ZD7155. Immuno-fluorescence demonstrated positive staining for angiotensin II AT1 receptor in the bladder wall, with high intensity in the mucosal epithelium (n=5). Angiotension II also increased the contractile activity in mucosa-intact muscle strips (µN/mg tissue, median (25%-75% range); control: 22.5 (2.9 – 1046.6) vs. 1µM angiotensin II: 148.0 (19.6 – 1483.7); n=7, p<0.05, Wilcoxon signed rank test). These data provide the first evidence that angiotensin II receptor AT1 is expressed in the bladder urothelium and angiotensin II stimulates ATP release from the urothelium via AT1 receptors. Angiotensin II is also able to generate a positive inotropic effect on mucosa-intact smooth muscle, partly through a paracrine effect of the released ATP. These findings suggest the significance of angiotension II and urothelial AT1 receptor in bladder physiology and pathophysiology.