Effect of tadalafil on chronic pelvic pain and prostatic inflammation in a rat model of experimental autoimmune prostatitis

Background Experimental autoimmune prostatitis (EAP) shares important clinical features with clinical chronic prostatitis/chronic pelvic pain. We investigated the effect of tadalafil on pelvic pain and prostatic inflammation in a rat EAP model. Methods EAP was induced in rats by intradermal injection of rat prostate antigen and complete Freund's adjuvant on days 0 and 28. Rats were treated with tadalafil (2 mg/kg, p.o.; EAP‐tadalafil) or vehicle (EAP‐vehicle) once daily from day 0, while sham‐operated animals were treated with vehicle only (Sham). Tactile allodynia was measured on days 28, 35, and 42 by applying von Frey filaments to the lower abdomen as an index of pelvic pain. On day 42, the plasma immunoglobulin G (IgG) concentration and the testosterone/estradiol ratio were measured and histopathological analysis of the prostate was performed. Results Tactile allodynia in the pelvic region was observed on days 28, 35, and 42 after EAP induction. The tactile allodynia observed on day 42 was significantly reduced by repeated treatment with tadalafil. Plasma IgG concentrations increased after EAP induction but the increase was not changed by tadalafil treatment. Prostate tissues were characterized by epithelial necrosis, infiltration of neutrophils and/or lymphocytes to acini and stroma, and fibrosis, in addition to a high stroma‐to‐epithelium ratio. Tadalafil treatment significantly suppressed the severity of the lesions. Conclusions EAP rats developed pelvic pain, prostatic inflammation and increased plasma IgG concentrations. Tadalafil inhibited the chronic pelvic pain and prostatic inflammation, suggesting that its anti‐inflammatory action may contribute to its blocking of pain development in the EAP model.