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 μm). 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-N^G-nitro arginine (l-NOARG; 0.3–100 μm) but not by d-N^G-nitro arginine. The inhibitory effect of l-NOARG on transmission was antagonized by l-arginine (100 μm), a NO precursor, but not by d-arginine. 4 Incubation with methylene blue (10–50 μm), 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.