Abstract
Plant is a good source of bioactive compounds. On the screen of Thai medicinal plant extracts on PDE5 inhibitory activity, ethanolic extract of Eulophia macrobulbon (E.C. Parish & Rehb. f.) Hook. f. (EM), a plant belonging to the Orchidaceae, showed promising PDE5 inhibition. Thus, the present study aimed to study the effects and mechanism involved of the EM on human cavernosum. Studies were performed in vitro on isolated Human cavernosal (HC) strips obtained from patients who had undergone for a sex change operation (n=6). Using pharmacological approach to elucidate the mechanism of the EM affected on the HC strips. Results found that EM (0.1-100 mg/ml) caused relaxation in phenylephrine pre-contracted HC strip in a concentration-dependent manner. This effect was not modified by pre-incubation of the HC strip with N-nitro-L-arginine (L-NA); a nitric oxide synthase inhibitor, ODQ; a soluble guanylate cyclase inhibitor, TEA or glybenclamide. EM potentiated relaxation of the HC strip precontracted with phenylephrine in a similar way as that of sildenafil. Nifedipine, a voltage-gated Ca+2-channel blocker, depressed the contraction of the HC strip to phenyleprine; when EM was also added, a further depression was found. In conclusion, EM caused relaxation of the Human cavernosum, the mechanism responsible for this might be due to EM poses PDE5 inhibitor activity. It is unlikely that EM stimulated release of nitric oxide, acts as a guanylate cyclase stimulator or as a voltage-gated Ca+2 channel inhibitor. Further study to identify the PDE5 inhibitory substance(s) of the EM is in progress.
