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Received for publication March 9, 2005.
Revised May 19, 2005.
Accepted for publication June 14, 2005.
The Rho-kinase pathway mediates Ca2+ sensitization in the penile circulation, which maintains the penis in the flaccid state. We aimed to investigate the functional effect of a novel Rho-kinase inhibitor (H-1152), both in vitro and in vivo as well as to demonstrate the expression of Rho guanine nucleotide exchange factors (RhoGEFs) in the rat corpus cavernosum (CC), by using a semi-quantitative RT-PCR assay to measure their mRNA expression. Cumulative addition of H-1152 (0.001-3 µM) or Y-27632 (0.01-30 µM) caused sustained relaxations of precontracted CC strips, which were not affected by inhibition of the nitric oxide signaling pathway. Addition of H-1152 (0.1 µM), Y-27632 (1 µM) or sodium nitroprusside (SNP, 0.1 µM) caused rightward shifts in the curves to phenylephrine (PE), but had little effect on the contractions mediated by electrical field stimulation (EFS). Interestingly, when H-1152 or Y-27632 was combined with SNP, a marked synergistic inhibition was noted both on PE- and EFS-induced contractions. Intraperitoneal administration of H-1152 (100 nmol/kg) had a discrete effect on mean arterial pressure and significantly enhanced erectile responses evoked by stimulation of the cavernous nerve. The mRNA expression for PDZ-RhoGEF, p115RhoGEF and LARG in cavernosal segments was visualized by electrophoresis on agarose gel. The results indicate that H-1152 is a powerful Rho-kinase inhibitor, giving rise to its therapeutic potential in the treatment of erectile dysfunction. The RGS-containing RhoGEFs may represent key components of the molecular mechanisms associated with the abnormal function of the cavernosal smooth muscle.
Key words:
H-1152, Rho-kinase, RhoA, RhoGEFs, calcium sensitization, nitric oxide
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