The relaxation effects of ginseng saponin in rabbit corporal smooth muscle: Is it a nitric oxide donor?

Objective. To determine whether crude extracts of ginseng saponin (GCS), containing the active ingredients from Panax ginseng and used as an aphrodisiac in oriental countries, relax corpus cavernosal smooth muscle in the rabbit. Materials and methods. Corpus cavernosal strips were prepared from rabbit penises. Isometric tension changes, recorded with a pressure transducer, in response to various drugs and electrical stimulation were assessed in an organ chamber, after active muscle tone had been induced by 10 μmol/L phenylephrine. Results. GCS (0.2-8.0 mg) relaxed the smooth muscle of rabbit corpus cavernosum (SMRCC) pre-contracted with phenylephrine in a dose-dependent manner. GCS at 0.75 mg significantly enhanced the relaxation of SMRCC induced by electrical field stimulation. The relaxation induced by 0.2-8.0 mg GCS was significantly attenuated by atropine (1 μmol/L), methylene blue (100 μmol/L) and N-omega-nitro-L-arginine methyl ester (L-NAME, 10 μmol/L). However, there was no significant difference in the attenuation of GCS-induced relaxation of SMRCC by adding vasoactive intestinal peptide antagonists or indomethacin. In addition, the decreasing rate of GCS-induced relaxation of SMRCC by methylene blue and L-NAME, was greater than that by atropine. L-arginine (10 mmol/L) reversed the inhibitory effect induced by L-NAME (1 mmol/L) on the attenuation of GCS-induced relaxation. Conclusions. These data suggest that GCS, as a nitric oxide donor, induces the relaxation of SMRCC through the L-arginine/nitric oxide pathway. For the clinical application of ginseng saponin, further studies are required to clarify the active subfraction(s) of GCS.