[A Case of Small Cell Carcinoma of the Urethra].

We report a case of small cell carcinoma of the urethra with inguinal lymph node metastases. A 50- year-old female patient presented with gross hematuria. Cystoscopy and computed tomography (CT) revealed a tumor surrounding the urethra and an inguinal lymphadenopathy. Biopsy of the urethral tumor demonstrated small cell carcinoma. Four courses of chemotherapy with etoposide and cisplatin, followed by 66 Gy of irradiation achieved complete remission. Unfortunately, 14 months later, positroemission-CT scan revealed recurrence of inguinal lymph node metastases. Although seven courses of chemotherapy with nogitecan were carried out, a new metastatic bone tumor developed. Amrubicin was administered as a third-line treatment, but was canceled after one course because of side effects. The patient died at 39 months after diagnosis. Small cell carcinoma of urethra with metastases has extremely poor prognosis, as is demonstrated by this case.

[A Case of Intra-Abdominal Testicular Cancer Occurring from an Overlooked Intra-Abdominal Testis in Undescended Testicular Surgery].

Here, we report an adult case of intra-abdominal testicular cancer after surgical treatment of an undescended testis in infancy. A 36-year-old male patient was accidentally diagnosed with a tumor in the pelvic cavity by ultrasonographic examination. He had hematuria and the human chorionic gonadotropin beta subunit level was slightly elevated. T2-weighedmagnetic resonance imaging revealed a well-defined and highly intense mass. Since these findings suggested intra-abdominal testicular cancer, laparoscopic surgery was performed to remove the mass. Laparoscopy revealed an intra-abdominal tumor accompanied by a looping vas deferens entering the left inguinal canal. The distal part of the looping vas had already been removed from the external inguinal ring. The pathological findings revealed a pT1 seminoma. The patient has been recurrence-free for 12 months. The present case implies the importance of careful investigation and treatment for intra-abdominal testicular cancer, since intra-abdominal testis might have been overlooked at the time of surgery for undescended testis.

Flavonoid Nobiletin Attenuates Cyclophosphamide-Induced Cystitis in Mice through Mechanisms That Involve Inhibition of IL-1ß Induced Connexin 43 Upregulation and Gap Junction Communication in Urothelial Cells.

Bladder inflammatory diseases cause various urinary symptoms, such as urinary frequency and painful urination, that impair quality of life. In this study, we used a mouse model of cyclophosphamide (CYP)-induced bladder inflammation and immortalized human urothelial (TRT-HU1) cells to explore the preventive potential of nobiletin (NOB), a polymethoxylated flavone enriched in citrus fruit peel, and investigate its mechanism of action in the bladder. Prophylaxis with PMF90 (60% NOB) attenuated the development of bladder inflammation and urinary symptoms in CYP-treated mice. PMF90 also reduced the upregulation of connexin 43 (Cx43), a major component of gap junction channels, in the bladder mucosa of CYP-treated mice. Stimulation of TRT-HU1 cells with the pro-inflammatory cytokine IL-1ß increased Cx43 mRNA and protein expression and enhanced gap junction coupling-responses that were prevented by pre-treatment with NOB. In urothelium-specific Cx43 knockout (uCx43KO) mice, macroscopic signs of bladder inflammation and changes in voiding behavior induced by CYP treatment were significantly attenuated when compared to controls. These findings indicate the participation of urothelial Cx43 in the development of bladder inflammation and urinary symptoms in CYP-treated mice and provide pre-clinical evidence for the preventive potential of NOB through its anti-inflammatory effects on IL-1ß signaling and urothelial Cx43 expression.

Bmal1 Regulates Prostate Growth via Cell-Cycle Modulation.

The circadian clock system exists in most organs and regulates diverse physiological processes, including growth. Here, we used a prostate-specific Bmal1-knockout mouse model (pBmal1 KO: PbsnCre+; Bmal1fx/fx) and immortalized human prostate cells (RWPE-1 and WPMY-1) to elucidate the role of the peripheral prostate clock on prostate growth. Bmal1 KO resulted in significantly decreased ventral and dorsolateral lobes with less Ki-67-positive epithelial cells than the controls. Next, the cap analysis of gene expression revealed that genes associated with cell cycles were differentially expressed in the pBmal1 KO prostate. Cdkn1a (coding p21) was diurnally expressed in the control mouse prostate, a rhythm which was disturbed in pBmal1 KO. Meanwhile, the knockdown of BMAL1 in epithelial RWPE-1 and stromal WPMY-1 cell lines decreased proliferation. Furthermore, RWPE-1 BMAL1 knockdown increased G0/G1-phase cell numbers but reduced S-phase numbers. These findings indicate that core clock gene Bmal1 is involved in prostate growth via the modulation of the cell cycle and provide a rationale for further research to link the pathogenesis of benign prostatic hyperplasia or cancer with the circadian clock.

Urothelium-Specific Deletion of Connexin43 in the Mouse Urinary Bladder Alters Distension-Induced ATP Release and Voiding Behavior.

Connexin43 (Cx43), the main gap junction and hemichannel forming protein in the urinary bladder, participates in the regulation of bladder motor and sensory functions and has been reported as an important modulator of day-night variations in functional bladder capacity. However, because Cx43 is expressed throughout the bladder, the actual role played by the detrusor and the urothelial Cx43 is still unknown. For this purpose, we generated urothelium-specific Cx43 knockout (uCx43KO) mice using Cre-LoxP system. We evaluated the day-night micturition pattern and the urothelial Cx43 hemichannel function of the uCx43KO mice by measuring luminal ATP release after bladder distention. In wild-type (WT) mice, distention-induced ATP release was elevated, and functional bladder capacity was decreased in the animals' active phase (nighttime) when Cx43 expression was also high compared to levels measured in the sleep phase (daytime). These day-night differences in urothelial ATP release and functional bladder capacity were attenuated in uCx43KO mice that, in the active phase, displayed lower ATP release and higher functional bladder capacity than WT mice. These findings indicate that urothelial Cx43 mediated ATP signaling and coordination of urothelial activity are essential for proper perception and regulation of responses to bladder distension in the animals' awake, active phase.

Hunner lesion versus non-Hunner lesion interstitial cystitis/bladder pain syndrome.

BACKGROUND: Global consensus on the standardization of terminology for interstitial cystitis/bladder pain syndrome is lacking and is in the formative stages. The Workshop on Hunner lesion versus non-Hunner lesion at the 2018 International Consultation on Interstitial Cystitis Japan discussed prevalence, performance and outcome of endoscopy, the role of histopathology, and markers. METHODS: A panel of experts reviewed the literature regarding Hunner lesion vs. non-Hunner lesion interstitial cystitis/bladder pain syndrome. RESULTS: The prevalence of Hunner lesion has been reported to be 5-57%. Older age and smaller anatomic bladder capacity were associated with Hunner lesions. Cystoscopy using local anesthesia is not adequate in diagnosing interstitial cystitis but is needed to rule out confusable diseases. Cystoscopy with hydrodistention and redistention of the bladder is considered standard. A Hunner lesion is visualized as a quite typical inflammatory reaction: a reddened mucosal area with small vessels radiating towards a central scar, splitting at distension, usually associated with a waterfall bleeding pattern. Biopsies from the inflamed area show inflammatory infiltrates, granulation tissue, detrusor mastocytosis, and fibrin deposits. Ablation of Hunner lesions includes transurethral resection of lesions, fulguration, laser ablation, and cortical steroid injections. Mast cell density is a somewhat controversial matter, described differently in different studies: marked increase in Hunner lesion vs. non-Hunner lesion in the majority of studies, no difference in a few. Nitric oxide appears to be a definitive marker in distinguishing Hunner lesion vs. non-Hunner lesion disease. Macrophage migration inhibitory factor is elevated in Hunner lesion patients. Increased level of urinary proinflammatory genes expression has also been found in Hunner lesion subjects. CONCLUSIONS: Hunner lesion patients are clinically and pathologically distinct from non-Hunner lesion bladder pain syndrome patients.

Low bladder capacity is an important predictor for comorbidity of interstitial cystitis with Hunner's lesion in patients with refractory chronic prostatitis/chronic pelvic pain syndrome.

OBJECTIVE: To evaluate the predictive factors for comorbidity of Hunner-type interstitial cystitis in patients with chronic prostatitis/chronic pelvic pain syndrome using urethrocystoscopy. METHODS: Thirty-two male patients were included in this study. Between April 2012 and April 2016; they were diagnosed with chronic prostatitis/chronic pelvic pain syndrome according to the National Institutes of Health classification. Their symptoms were not improved by 3 months of behavioral and pharmacological therapies. They all underwent narrow band imaging-assisted urethrocystoscopy to assess whether the presence of Hunner's lesions correlated with other variables. RESULTS: Thirteen out of 32 patients (41%) had Hunner's lesions. Of the variables, maximal voided volume per micturition (106 ± 29 mL vs 171 ± 61 mL) and bladder capacity (267 ± 121 mL vs 407 ± 137 mL) were significantly smaller in patients with Hunner's lesions compared to those without. Other variables, apart from age, were not significantly different. Furthermore, patients with voided volume less than 150 mL were more likely to have Hunner's lesions than those with voided volume exceeding 150 mL. CONCLUSIONS: Hunner-type interstitial cystitis is a common comorbidity among patients with refractory chronic prostatitis/chronic pelvic pain syndrome. In cases where voided volume is small, performing narrow band imaging-assisted urethrocystoscopy would be very helpful for detecting bladder mucosal changes such as Hunner's lesions.

[Usefulness of comparing of magnetic resonance imaging (MRI) findings prior to repeat biopsy and negative initial biopsy as a decision-making method for repeat prostate biopsy].

We retrospectively reviewed the data from a cohort of 44 patients with one initial negative transrectal ultrasound-guided prostate biopsy who underwent a repeat biopsy from 2006 to 2013. At each biopsy session, we checked patient age, serum prostate specific antigen (PSA), prostate volume, PSA density, PSA velocity, months from the initial biopsy session, multiparametric magnetic resonance imaging (MRI) findings (T2-weighted, dynamic contrast-enhanced and diffusion-weighted, 1.5 Tesla pelvic-phased array) prior to repeat biopsy and initial negative biopsy. Mean age was 68.2±8.82 years. PSA was 11.5±7.65 ng/ml before repeat biopsy. Prostate cancer was detected in 15 (34.0%) patients at repeat biopsy. In univariate and multivariate analysis, positive MRI findings before repeat biopsy were significant independent predictors of a positive repeat biopsy. At per patient analysis, the sensitivity, specificity, positive and negative predictive values were 66.6, 68.9, 71.4 and 80.0% for MRI before repeat biopsy. No suspicious lesion on MRI before repeat biopsy was relevant to negative biopsy. According to the comparison of MRI findings prior to repeat biopsy and negative initial biopsy, suspicious MRI findings at the peripheral zone before repeat biopsy and initial negative biopsy were relevant to a high cancer detection rate (83.3%) at repeat prostate biopsy. These results suggested that the absence of a suspicious lesion on MRI before repeat biopsy could guide the avoidance of repeat biopsy and suspicious MRI findings at the peripheral zone before repeat biopsy and initial negative biopsy could guide repeat biopsy.

A prospective comparative study of intravesical bacillus Calmette-Guérin therapy with the Tokyo or Connaught strain for nonmuscle invasive bladder cancer.

PURPOSE: We prospectively compared the efficacy and adverse events of the bacillus Calmette-Guérin Tokyo 172 and Connaught strains for nonmuscle invasive bladder cancer. MATERIALS AND METHODS: Between January 2004 and May 2012 patients with pTa/T1 and pTis, multiple tumors and a recurrence-free period of 3 months or less who required intravesical bacillus Calmette-Guérin therapy were prospectively allocated randomly to receive the Tokyo or Connaught strain. The primary study end points were the complete response rate in patients with pTis and concomitant carcinoma in situ (pTa or pT1), recurrence-free survival in patients with pTa, pT1 and carcinoma in situ who achieved a complete response after therapy and the frequency of adverse events. RESULTS: Administration of the Connaught strain ceased because its production was suspended in June 2012. Therefore, analysis was performed using data gathered to date. Overall, 66 and 63 patients who received the Tokyo and Connaught strains, respectively, were included in efficacy analysis. Patient and tumor characteristics were well balanced between the 2 groups. Median followup was 855 days. Adverse events were similar in the groups. The complete response rate was 90.3% and 85.0% in patients given the Tokyo and Connaught strains, respectively, which did not significantly differ (p = 0.896). The 2-year recurrence-free survival rate was 73.2% and 68.8%, respectively. CONCLUSIONS: Results suggest no significant differences between the Tokyo and Connaught strains in the complete response, recurrence-free survival or adverse event rate.

[Percutaneous renal mass biopsy after indeterminate diagnostic imaging results].

We conducted a retrospective study to examine the efficacy of renal mass biopsies in our hospital. Twenty-six patients (18 male, 8 female ; median age, 69 years ; range, 42-85 years) with renal masses were divided into two groups. Group 1 (n＝9) underwent renal mass biopsies after completion of diagnostic imaging tests that needed a pathological diagnosis before treatment other than extirpative surgery, and group 2 (n＝17) underwent renal mass biopsies after completion of indeterminate diagnostic imaging tests that did not rule out malignancy. The median tumor size was 2.8cm (range, 0.8-15 cm), and the median number of biopsy cores obtained was two (range, 2-4). There were no biopsy-associated complications that required intervention. In group 1, 100% (9 of 9) of the renal mass biopsies were diagnostic, and the pathological findings corresponded to the respective diagnosis obtained by imaging tests, most of which were clear cell carcinoma. In group 2, 59% (10 of 17) of the biopsies were diagnostic. The imaging characteristics of the seven nondiagnostic biopsies in group 2 were low blood flow and poor peripheral clarity. On the other hand, renal mass biopsies were indispensable for some patients in group 2 in whom the pathological findings led to a decision of treatment strategy. In conclusion, renal mass biopsies should be considered in view of their ability to compensate for limitations of imaging tests and their low frequency of complications.

[The factors for continuing docetaxel-based chemotherapy for castration-resistant prostate cancer].

A cohort of patients with castration-resistant prostate cancer (CRPC) that were treated with docetaxel (DOC) were retrospectively analyzed in order to examine the factors for continuing DOC therapy. In total, 26 patients treated with DOC at our hospital from August 2007 to August 2011 were recruited into the study. The participants were divided into two groups ; the first comprising 13 patients who received short-term DOC therapy (less than 5 cycles) and the second comprising 13 who received long-term DOC therapy (5 or more cycles). There was no significant difference in the indicators including age, prostate specific antigen level (at initial diagnosis), clinical stage and Gleason score between the groups. Patients with pain or poor performance status were more likely to be found in the short-term DOC group. The Hemoglobin-level was significantly higher in the long-term DOC group. In contrast, alkaline phosphatase, lactate dehydrogenase and C-reactive protein levels were significantly higher in the short-term DOC group. The period from the start of primary endocrine therapy to CRPC diagnosis was significantly longer in the long-term DOC group (p=0.0008). This latter finding suggests that DOC therapy can be continued for a longer time, in CRPC cases which have a long-term response to endocrine therapy, and may be associated with a more favorable survival outcome. However, to validate this suggestion, further investigation with a larger cohort of cases is necessary.

[A multi-institutional questionnaire survey on surgical treatment for a small renal mass: factors related with decision-making in indications for partial nephrectomy].

This study aimed to investigate factors taken into account when considering the indication of partial nephrectomy (PN). In October 2011, a questionnaire prepared with reference to the American Urological Association small renal mass survey and RENAL nephrometry score, and focusing on the factors taken into account when considering the use of PN, such as differences among candidates for open PN or laparoscopic PN was sent to 40 institutions. We received replies from 32 of the 40 institutions (average 611 beds) to which the questionnaire was sent. The total number of surgeries performed for renal tumors at the 32 institutions was 844 in 2009 and 889 in 2010. The number of PNs performed was 174 in 2009 (open : 61, laparoscopic : 113), and 241 in 2010 (open : 103, laparoscopic : 138), which represents a 38.3% increase. All respondents reported that renal function prior to PN was considered to be important, followed by tumor size, tumor number, and hereditariness. There were significantly more indications for open PN than for laparoscopic PN, and they were based on tumor size, degree of protrusion, and distance from the renal sinus. In addition, a clear tendency toward avoiding laparoscopic PN for cystic renal cancer was found. In addition, the institutions with a larger number of PNs tended to indicate more complicated cases including larger tumor size or entirely endophytic cases. This study has a limitation in that it was intended for a relatively large hospital, but these results can be useful information for institutions that are considering the introduction of open or laparoscopic PN.

[A case of retroperitoneal liposarcoma with inflammatory pseudotumor].

A 54-year-old man presented with pollakiuria and dysuria. Ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI) showed a retroperitoneal tumor 10 cm in diameter. Pathological examination of a transrectal biopsy specimen obtained from the patient revealed the presence of an inflammatory myofibroblastic tumor (IMT). The patient underwent surgical resection of the tumor. Histopathologically, the tumor was composed of 3 parts : the largest part was compatible with an inflammatory pseudotumor: the second part, well-differentiated liposarcoma: and the third part, a myxoid liposarcoma. He has been followed up for 14 months ; but there was no evidence of local recurrence of the tumor. We believe that the inflammatory pseudotumor complicated in repairing the inflammation arising from the liposarcoma.

[Age-related Epstein-Barr virus-associated lymphoproliferative disorder presenting as rapidly developing renal mass].

An 83-year-old man visited our department with a slightly enhanced mass of about 2 cm in diameter, detected incidentally in the left kidney on computed tomography (CT) performed for other reasons in a different department. Fluorodeoxyglucose-positron emission tomography was performed under the suspicion of metastatic renal tumor and malignant lymphoma. Accumulation was observed in the mass but not in other regions. The tumor size was about 2 mm on CT 4 months previously, indicating rapid enlargement. Based on these observations, a malignant renal tumor was diagnosed and laparoscopic left nephrectomy was performed. Pathologic examination revealed relatively large cells diffused within a background of many small lymphocytes and histiocytes. The large cells were positive when tested by Epstein-Barr virus (EBV)-encoded RNA in situ hybridization. No clinically apparent immunodeficiency was observed, suggesting age-related EBV-associated lymphoproliferative disorder caused by an underlying age-related reduction in immunocompetence. This is the first report of a kidney-localized case in Japan.

[Bilateral renal cell carcinoma of dialysis patient manifesting as spontaneous renal rupture].

A 50-year-old male had been maintained on hemodialysis for 12 years because of chronic renal failure. The patient experienced sudden left flank pain. Computed tomography (CT) showed a huge left perirenal hematoma, which was diagnosed as a spontaneous rupture of the left kidney. CT also showed multiple cysts in both kidneys and a right renal tumor suspected to be renal cell carcinoma. Although the cause of the rupture was unknown, bilateral nephrectomy was performed. Histological study revealed acquired cystic disease of the kidney (ACDK) with bilateral renal cell carcinoma. Our diagnosis was rupture of the renal cell carcinoma. The patient was free of recurrence at 17 months postoperatively. To our knowledge, this case is the fifth report of renal cell carcinoma in ACDK manifesting as spontaneous rupture in the Japanese literature.

[A case report: recurrence of urothelial cancer in an ileal conduit].

A 48-year-old man presented complaining of lower abdominal pain, and was diagnosed with invasive bladder cancer. After neoadjuvant chemotherapy, cystoprostatourethrectomy and ileal conduit diversion were performed. At 53 years of age, bladder cancer recurred in the upper urinary tract and he underwent complete urinary tract extirpation. Histological examination revealed an urothelial carcinoma in an ileal conduit. Three years later, a local recurrence led to combined modality therapy including chemotherapy and radiotherapy. He is receiving maintenance chemotherapy for metastatic tumors. Urothelial carcinoma arising in an ileal conduit after radical cystectomy for bladder cancer is infrequently reported. To our knowledge, only 12 cases, including ours, have been reported.

[Post-operative recurrence patterns of urothelial tumors in the upper urinary tract: comparison between renal pelvic and ureteral tumors].

To determine treatment outcomes for renal pelvic and ureteral tumors, we retrospectively evaluated the correlations between stage, area oflymphadenectomy (LND) and the recurrence pattern. Of 162 patients treated surgically for a urothelial tumor of the upper urinary tract from 1990 to 2006, we reviewed 57 renal pelvic and 55 ureteral, diagnosed as having either renal pelvic or ureteral tumors. We defined local recurrence as metastasis to the retroperitoneum, pelvis, and abdominal lymph nodes. Of the 112 patients, LND was performed in 76. No patient with pTis/a/1 disease showed pN(+); however, in pT2 < or = disease, 39% of the renal pelvis and 23% of the ureter cases exhibited nodal involvement. During follow up, 35 patients had relapse; 25 distant metastasis, 5 local recurrence, and 5 synchronous recurrence at both sites. In pT2/3 disease, the frequency of distant metastasis of a ureteral tumor was significantly higher than that in renal pelvic cases (55% vs. 19%, P = 0.0237). Local recurrence was found in 7 renal pelvic and 3 ureteral cases. Although all of these patients had previously undergone LND, local recurrence adjacent to the dissected area was confirmed in 6 cases. In pT2 < or = disease, ureteral tumors showed more frequent occurrences of distant metastasis, whereas local relapses adjacent to the dissected nodal areas were more prominent in renal pelvic cases. When deciding a therapeutic strategy in renal pelvic cases, careful consideration about an adequate region for LND appears important.

Circadian coordination of ATP release in the urothelium via connexin43 hemichannels.

Day-night changes in the storage capacity of the urinary bladder are indispensable for sound sleep. Connexin 43 (Cx43), a major gap junction protein, forms hemichannels as a pathway of ATP in other cell types, and the urinary bladder utilizes ATP as a mechanotransduction signals to modulate its capacity. Here, we demonstrate that the circadian clock of the urothelium regulates diurnal ATP release through Cx43 hemichannels. Cx43 was expressed in human and mouse urothelium, and clock genes oscillated in the mouse urothelium accompanied by daily cycles in the expression of Cx43 and extracellular ATP release into the bladder lumen. Equivalent chronological changes in Cx43 and ATP were observed in immortalized human urothelial cells, but these diurnal changes were lost in both arrhythmic Bmal1-knockout mice and in BMAL1-knockdown urothelial cells. ATP release was increased by Cx43 overexpression and was decreased in Cx43 knockdown or in the presence of a selective Cx43 hemichannel blocker, which indicated that Cx43 hemichannels are considered part of the components regulating ATP release in the urothelium. Thus, a functional circadian rhythm exists in the urothelium, and coordinates Cx43 expression and function as hemichannels that provide a direct pathway of ATP release for mechanotransduction and signalling in the urothelium.

A Prospective Randomized Trial Comparing a Combined Regimen of Amikacin and Levofloxacin to Levofloxacin Alone as Prophylaxis in Transrectal Prostate Needle Biopsy.

PURPOSE: We investigated whether addition of amikacin to levofloxacin-based antimicrobial prophylaxis reduces febrile urinary tract infections after transrectal ultrasound-guided prostate needle biopsy (TRUSB). MATERIALS AND METHODS: A total of 447 patients undergoing TRUSB were prospectively randomized into two groups. The 230 patients in Group A were given one oral dose of levofloxacin 400 mg prior to TRUSB; the 217 patients in Group B each received the same dose of levofloxacin and one 200 mg intravenous dose of amikacin. Patients' characteristics were assessed prior to TRUSB and their symptoms were checked after the TRUSB. RESULTS: Both regimens were well tolerated with no side effects. No statistically significant difference in patients' characteristics, or in incidence of inflammation- or infection-related symptoms was seen between the two groups; nor any significant difference among those who developed fever and those who did not. Two Group A patients and one Group B patient developed febrile urinary tract infections. Accountable pathogens determined by urine and blood cultures were fluoroquinolone-resistant E.coli and extended-spectrum ß-lactamase-producing E.coli. All pathogens isolated were levofloxacin-resistant, amikacin-susceptible species. CONCLUSION: Although the present study was under-powered by unexpectedly low overall incidence of febrile urinary tract infections, addition of one intravenous administration of amikacin to one oral administration of levofloxacin showed no advantage compared with levofloxacin alone as antimicrobial prophylaxis in TRUSB. Strikingly, all pathogens isolated from febrile patients were sensitive to amikacin in vitro. Therefore, further understanding of amikacin's drug kinetics in the prostate is necessary to develop a more efficient drug delivery system for amikacin.

Intravital imaging of mouse urothelium reveals activation of extracellular signal-regulated kinase by stretch-induced intravesical release of ATP.

To better understand the roles played by signaling molecules in the bladder, we established a protocol of intravital imaging of the bladder of mice expressing a Förster/fluorescence resonance energy transfer (FRET) biosensor for extracellular signal-regulated kinase (ERK), which plays critical roles not only in cell growth but also stress responses. With an upright two-photon excitation microscope and a vacuum-stabilized imaging window, cellular ERK activity was visualized in the whole bladder wall, from adventitia to urothelium. We found that bladder distention caused by elevated intravesical pressure (IVP) activated ERK in the urothelium, but not in the detrusor smooth muscle. When bladder distension was prevented, high IVP failed to activate ERK, suggesting that mechanical stretch, but not the high IVP, caused ERK activation. To delineate its molecular mechanism, the stretch-induced ERK activation was reproduced in an hTERT-immortalized human urothelial cell line (TRT-HU1) in vitro. We found that uniaxial stretch raised the ATP concentration in the culture medium and that inhibition of ATP signaling by apyrase or suramin suppressed the stretch-induced ERK activation in TRT-HU1 cells. In agreement with this in vitro observation, pretreatment with apyrase or suramin suppressed the high IVP-induced urothelial ERK activation in vivo. Thus, we propose that mechanical stretch induces intravesical secretion of ATP and thereby activates ERK in the urothelium. Our method of intravital imaging of the bladder of FRET biosensor-expressing mice should open a pathway for the future association of physiological stimuli with the activities of intracellular signaling networks.