Viagra Research Today is a free monthly online journal that collates and summarizes the latest research about Viagra, including details on sildenafil, erectile dysfunction, impotence, side-effects, alternatives. | ||||||||
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Erection capability is potentiated by long-term sildenafil treatment: role of blood flow-induced endothelial nitric-oxide synthase phosphorylation.Musicki B, Champion HC, Becker RE, Liu T, Kramer MF, Burnett AL Department of Urology, Johns Hopkins Hospital, Marburg 405, 600 North Wolfe St., Baltimore, MD 21287, USA. bmusicki@jhmi.edu Despite demonstrated clinical efficacy of sildenafil for the temporary treatment of erectile dysfunction, the possibility that sildenafil used long-term durably augments erectile ability remains unclear. We investigated whether continuous long-term administration of sildenafil at clinically relevant levels to aged rats "primes" the penis for improved erectile ability and involves nitric oxide (NO) or RhoA/Rho-kinase signaling pathways. In aged, but not young rats, sildenafil prolonged erection and increased the protein expressions of phosphorylated endothelial NO synthase (eNOS) at serine-1177 and phosphorylated Akt at serine-473 in penes. Only in the young rat penis, protein expressions of phosphodiesterase-5 and phosphomyosin phosphatase target subunit 1, a marker of Rho-kinase activity, were increased by sildenafil. Sildenafil inhibited phosphodiesterase-5 activity in penes of young and aged rats coincident with assayed free plasma levels of the drug equivalent to clinically therapeutic measurements. We conclude that erectile ability can be enhanced under preconditions of erectile impairment by long-term inhibition of phosphodiesterase-5 and that the effect is mediated by Akt-dependent eNOS phosphorylation. The lack of erectile ability enhancement in young rats by long-term phosphodiesterase-5 inhibition may relate to restrained NO signaling by phosphodiesterase-5 up-regulation, lack of incremental Akt and eNOS phosphorylation, and heightened Rho-kinase signaling in the penis. Published 16 June 2005 in Mol Pharmacol, 68(1): 226-32.
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