KMUP‐1 relaxes rabbit corpus cavernosum smooth muscle in vitro and in vivo: involvement of cyclic GMP and K+ channels

In isolated endothelium‐intact or denuded rabbit corpus cavernosum preconstricted with phenylephrine, KMUP‐1 (0.001 – 10 μM) caused a concentration‐dependent relaxation. This relaxation of KMUP‐1 was attenuated by endothelium removed, high K+ and pretreatments with a soluble guanylyl cyclase (sGC) inhibitor ODQ (1 μM), a NOS inhibitor L‐NAME (100 μM), a K+ channel blocker TEA (10 mM), a KATP channel blocker glibenclamide (1 μM), a voltage‐dependent K+ channel blocker 4‐AP (100 μM) and Ca2+‐dependent K+ channel blockers apamin (1 μM) and charybdotoxin (ChTX, 0.1 μM). The relaxant responses of KMUP‐1 (0.01, 0.05, 0.1 μM) together with a PDE inhibitor IBMX (0.5 μM) had additive actions on rabbit corpus cavernosum smooth muscle (CCSM). KMUP‐1 (0.01 – 10 μM) induced increase of intracellular cyclic GMP level in the primary cell culture of rabbit CCSM. This increase in cyclic GMP content was abolished in the presence of ODQ (10 μM). Both KMUP‐1 and sildenafil at 0.2, 0.4, 0.6 mg kg−1 caused increases of intracavernous pressure (ICP) and duration of tumescene (DT) in a dose‐dependent manner. These in vivo activities of ICP for sildenafil and KMUP‐1 are consistent with those of in vitro effects of cyclic GMP. KMUP‐1 has the following merits: (1) inhibition of PDE or cyclic GMP breakdown, (2) stimulation of NO/sGC/cyclic GMP pathway, and (3) subsequent stimulation of K+ channels, in rabbit CCSM. We suggest that these merits play prominent roles in KMUP‐1‐induced CCSM relaxation‐associated increases of ICP and penile erection. British Journal of Pharmacology (2002) 135, 1159–1166; doi:10.1038/sj.bjp.0704554