Assessment of heme oxygenase-1 (HO-1) activity in the cavernous tissues of sildenafil citrate-treated rats

Aim: To assess heme oxygenase‐1 (HO‐1) activity in the cavernous tissue of sildenafil citrate‐treated rats. Methods: One hundred and ninety‐two Sprague‐Dawley male rats, divided into four equal groups, were investigated. Group 1, the control group, received regular animal chow; group 2 received sildenafil citrate by intragastric tube; group 3 received sildenafil and HO inhibitor (zinc protoporphyrin, ZnPP); and group 4 received sildenafil and nitric oxide synthase (NOS) inhibitor L‐nitroarginine methyl ester (L‐NAME). Twelve rats from each group were killed after 0.5 h, 1 h, 2 h and 3 h of drug administration. Then HO‐1 activity, cGMP levels and NOS enzymatic activity in the cavernous tissues were estimated. Results: In cavernous tissue, HO‐1 activity, NOS enzymatic activity and cGMP concentration increased significantly in sildenafil‐treated rats compared to other groups throughout the experiment. Rats receiving either HO or NOS inhibitors showed a significant decrease in these parameters. HO‐1 cavernous tissue activity and NOS enzymatic activity demonstrated a positive significant correlation with cGMP levels (r= 0.646, r= 0.612 respectively; P < 0.001). Conclusion: The actions of PDE5 inhibitor sildenafil citrate in the cavernous tissue are partly mediated through the interdependent relationship between both HO‐1 and NOS activities.