title: Phentolamine relaxes human corpus cavernosum by a nonadrenergic mechanism activating ATP-sensitive K+ channel.
abstract: To investigate the pharmacodynamics of phentolamine in human corpus cavernosum (HCC) with special attention to the role of the K+ channels. Strips of HCC precontracted with nonadrenergic stimuli and kept in isometric organ bath immersed in a modified Krebs-Henseleit solution enriched with guanethidine and indomethacine were used in order to study the mechanism of the phentolamine-induced relaxation. Phentolamine caused relaxation (approximately 50%) in HCC strips precontracted with K+ 40 mM. This effect was not blocked by tetrodotoxin (1 microM) (54.6+/-4.6 vs 48.9+/-6.4%) or (atropine (10 microM) (52.7+/-6.5 vs 58.6+/-5.6%). However, this relaxation was significantly attenuated by L-NAME (100 microM) (59.7+/-5.8 vs 27.8+/-7.1%; P<0.05; n = 8) and ODQ (100 microM) (62.7+/-5.1 vs 26.8+/-3.9%; P<0.05; n = 8). Charybdotoxin and apamin (K(Ca)-channel blockers) did not affect the phentolamine relaxations (54.6+/-4.6 vs 59.3+/-5.2%). Glibenclamide (100 microM), an inhibitor of K(ATP)-channel, caused a significant inhibition (56.7+/-6.3 vs 11.3+/-2.3%; P<0.05; n = 8) of the phentolamine-induced relaxation. In addition, the association of glibenclamide and L-NAME almost abolished the phentolamine-mediated relaxation (54.6+/-5.6 vs 5.7+/-1.4%; P<0.05; n = 8). The results suggest that phentolamine relaxes HCC by a nonadrenergic-noncholinergic mechanism dependent on nitric oxide synthase activity and activation of K(ATP)-channel.
authors.affiliation: Surgery Department, Federal University of Ceara, Fortaleza, Ceara, Brazil. luciofl@secrel.com.br
authors.forename: L F G
authors.initials: LF
authors.lastname: Silva
authors.forename: N R F
authors.initials: NR
authors.lastname: Nascimento
authors.forename: M C
authors.initials: MC
authors.lastname: Fonteles
authors.forename: G
authors.initials: G
authors.lastname: de Nucci
authors.forename: M E
authors.initials: ME
authors.lastname: Moraes
authors.forename: P R L
authors.initials: PR
authors.lastname: Vasconcelos
authors.forename: M O
authors.initials: MO
authors.lastname: Moraes
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D001341:Autonomic Nervous System / Q000187:drug effects*; D006152:Cyclic GMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D010413:Penis / Q000187:drug effects*; D010646:Phentolamine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015221:Potassium Channels; D011189:Potassium Chloride / Q000494:pharmacology
chemical_list: D000317:Adrenergic alpha-Antagonists; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; D009569:Nitric Oxide; D011189:Potassium Chloride; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D006152:Cyclic GMP; D010646:Phentolamine