Relaxant mechanisms of 3, 5, 7, 3', 4'-pentamethoxyflavone on isolated human cavernosum

We have investigated effects and mechanisms responsible for the activity of 3, 5, 7, 3', 4'-pentamethoxyflavone (PMF) on isolated human cavernosum. PMF is the major flavone isolated from Kaempferia parviflora claimed to act as an aphrodisiac. PMF caused relaxation of phenylephrine precontracted human cavernosal strips, and this effect was slightly inhibited by N(G)-nitro-l-arginine, a nitric oxide synthase inhibitor, but not by ODQ (soluble guanylate cyclase inhibitor), TEA (tetraethylammonium, blocker of voltage-dependent K(+) channels) or glybenclamide (blocker of ATP-dependent K(+) channels). PMF did not significantly inhibit the relaxant activity of glyceryltrinitrate or acetylcholine on human cavernosal strips precontracted with phenylephrine. In contrast, sildenafil (phosphodiesterase inhibitor) potentiated the relaxant activity of glyceryl trinitrate but not of acetylcholine. In normal Krebs solution with nifedipine (blocker of l-type Ca(2+) channels), or in Ca(2+)-free Krebs solution, PMF caused a further inhibition of human cavernosum contracted with phenylephrine. In human cavernosum treated with thapsigargin (inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase) in Ca(2+)-free medium, PMF suppressed the concentration-response curve of human cavernosum to phenylephrine and a further suppression was found when SKF-96365 (a blocker of store-operated Ca(2+) channels and Y-27632 (inhibitor of Rho-kinase)), but not nifedipine, were added sequentially. Thus, PMF had only a weak effect on the release of nitric oxide, and had no effect as a K(ATP)- or K(Ca) channel opener, a phosphodiesterase inhibitor, a store-operated Ca(2+) channel blocker or a Rho-kinase inhibitor. Therefore, these studies suggest that PMF causes relaxation of human cavernosum through voltage-dependent Ca(2+) channels and other mechanisms associated with calcium mobilization.