Background: Up‐regulation of epithelial vascular endothelial growth factor (VEGF) expression was recently reported at an early stage of bladder carcinogenesis in rats. Subsequently, clotrimazole (CLT) was reported to exert an inhibitory effect on the in vitro proliferation of vascular endothelial cells stimulated by VEGF. The present study was performed to evaluate the effect of CLT on the initial stage of N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine (BBN)‐induced carcinogenesis of the urinary bladder in rats.

Methods: Seven‐week‐old‐female Wistar rats were divided into both a control group and the other four groups that were allowed free access to drinking water containing 0.05%BBN. Two groups of rats (10‐CLT and 20‐CLT) received CLT (100 mg/kg per day) once daily by gavage for 10 and 20 weeks, respectively. The other two groups of rats (10‐BBN and 20‐BBN) were maintained on the same BBN‐containing drinking water for 10 and 20 weeks, respectively, without receiving CLT. After removing the urinary bladder of each rat, expression of VEGF and VEGF receptor FLT1, and new capillaries were examined by immunohistochemical staining. VEGF mRNA was detected by the reverse transcription polymerase chain reaction.

Results: The ratio of VEGF‐positive cells and the expression of VEGF mRNA were lower in the 20‐CLT group than in the 10‐BBN group. Newly formed capillaries in the 20‐CLT group were significantly decreased compared with those in the 10‐BBN group.

Conclusion: These quantitative data suggested that CLT can inhibit VEGF expression in vivo and hence inhibit angiogenesis in the early stages of bladder carcinoma.