The effect of inhibitors of nitric oxide biosynthesis and cyclic GMP formation on nerve‐evoked relaxation of human cavernosal smooth muscle

Abstract

1. The inhibitory transmission in isolated preparations of cavernosal smooth muscle from human penis has been studied. 2. Electrical field stimulation (EFS; 2-64 pulses/train, 0.8 ms pulse duration, 10 Hz) evoked relaxation of preparations treated with guanethidine (50 microM). The EFS-evoked relaxations were atropine-resistant and tetrodotoxin-sensitive indicating their origin to be non-adrenergic, non-cholinergic (NANC) nerve stimulation. 3. EFS-evoked relaxation was attenuated dose-dependently by the nitric oxide (NO)-synthase inhibitor, L-NG-nitro arginine (L-NOARG; 0.3-100 microM) but not by D-NG-nitro arginine. The inhibitory effect of L-NOARG on transmission was antagonized by L-arginine (100 microM), a NO precursor, but not by D-arginine. 4. Incubation with methylene blue (10-50 microM), a known inhibitor of guanylate cyclase activation by NO, caused a concentration-related inhibition of EFS-evoked relaxation. 5. It is concluded that NANC nerve-evoked relaxation of human cavernosal smooth muscle is mediated by NO or a NO-like substance.