title: Sildenafil inhibits duodenal contractility via activation of the NO-K+ channel pathway.
abstract: Phosphodiesterase type-5 (PDE5) specifically cleaves cyclic guanosine monophosphate (cGMP), a key intracellular secondary messenger. The PDE5 inhibitor sildenafil is a well-known vasodilator that also has gastrointestinal myorelaxant properties. In the present study, we further investigated sildenafil-induced myorelaxation in rat isolated duodenum, assessing its interaction with nitric oxide (NO) synthase and K(+) channel opening. The spontaneous contractions of duodenal strips were reversibly inhibited by sildenafil (0.1-300 microM) in a concentration-dependent manner [mean (95% confidence interval); EC(50) = 6.8 (2.7-17.3) microM]. The sildenafil-induced myorelaxation was significantly decreased by the NO synthase inhibitor N-nitro-L-arginine methyl ester [increasing the EC(50) value to 41.9 (26.1-67.3) microM]. Sodium nitroprusside or forskolin pretreatments enhanced the sildenafil-induced myorelaxation. In isolated strips pretreated with BaCl(2) (0.2 mM), 4-aminopyridine (4-AP, 3 mM), or glybenclamide (1 microM), the sildenafil-induced EC(50) value was significantly increased to 32.8 (19.1-56.4), 27.1 (15.2-48.3) and 20.1 (16.4-24.7) microM, respectively. Minoxidil (50 microM) or diazoxide (100 microM) also significantly attenuated the sildenafil-induced potency. In conclusion, the NO synthase/cyclic nucleotide pathway activation is involved in sildenafil-induced inhibition of spontaneous duodenal contractions. Its pharmacological action seems to be influenced by K(+) channel opening, especially the voltage-sensitive ones, being inhibited by 4-AP and K(ATP) channels, sensitive to glybenclamide.
authors.affiliation: Departamento de Fisiologia e Farmacologia, Faculdade de Medicina, Universidade Federal do Ceará, Fortaleza, CE, Brazil.
authors.forename: Cristiano M
authors.initials: CM
authors.lastname: Clemente
authors.forename: Paula V
authors.initials: PV
authors.lastname: Araújo
authors.forename: Raimundo C
authors.initials: RC
authors.lastname: Palheta
authors.forename: Zoélia M L
authors.initials: ZM
authors.lastname: Ratts
authors.forename: Geórgea H
authors.initials: GH
authors.lastname: Fernandes
authors.forename: Francisco H
authors.initials: FH
authors.lastname: Rola
authors.forename: Ricardo B
authors.initials: RB
authors.lastname: de Oliveira
authors.forename: Armênio A
authors.initials: AA
authors.lastname: dos Santos
authors.forename: Pedro J C
authors.initials: PJ
authors.lastname: Magalhães
mesh_terms: D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D009599:Nitroprusside / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D020030:Nitric Oxide Donors; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D009599:Nitroprusside; D005576:Colforsin; D009569:Nitric Oxide; D000068677:Sildenafil Citrate; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D003981:Diazoxide; D019331:NG-Nitroarginine Methyl Ester