Mechanical irritation induces neurogenic inflammation in the rat urethra

A catheter was inserted into the urethral meatus of urethane-anaesthetized rats and rotated (30 rotations/minute) during a three minute period. One hour later, microvascular permeability in the distal urethra was evaluated by means of the Evans Blue leakage technique. Dye extravasation increased significantly (74 +/- 12 ng./mg. of wet tissue weight, p less than 0.05), as compared to control values (18 +/- 2 ng./mg.). The effect of catheterism was prevented by about 50% by systemic pretreatment with capsaicin performed in either adult or newborn rats, as well as by bilateral removal of pelvic ganglia. Furthermore, pretreatment with capsaicin of adult rats, combined to pelvic ganglionectomy, virtually abolished the inflammatory response produced by mechanical irritation of the urethra. These results indicate that: 1) the increase of vascular permeability produced by mechanical irritation is nerve-mediated, 2) capsaicin-sensitive afferents participate in the inflammatory process and 3) capsaicin-insensitive nerves, which pass through the pelvic ganglia, contribute to the overall response.