title: Adrenoceptor-mediated regulation of the contractility in horse penile resistance arteries.
abstract: The receptors mediating the contractions to both exogenously applied noradrenaline and electrical field stimulation (EFS) were characterized in horse isolated penile resistance arteries. The alpha 1-adrenoceptor-selective antagonist, prazosin, caused competitive rightward shifts of the contractile concentration-response curves (CRC) to phenylephrine. The alpha 2-antagonist, rauwolscine, also displaced to the right the CRC to the alpha 2-adrenoceptor-selective agonist, BHT 920. EFS (0.3 ms, 20-second trains) caused tetrodotoxin-sensitive frequency-dependent contractions which were enhanced in the presence of NG-nitro-L-arginine (L-NOARG, 3 x 10(-5) M), but not affected by mechanical endothelial cell removal. In experiments performed in the presence of L-NOARG, prazosin inhibited contractions to EFS, while rauwolscine inconsistently enhanced the contractile responses. Exogenously added noradrenaline induced contractions which were not changed in endothelium-denuded arteries, but significantly increased in the presence of L-NOARG. Prazosin inhibited the noradrenaline-induced contractions, while rauwolscine did not change the response to noradrenaline either alone or in the presence of prazosin. In the presence of phentolamine (10(-5) M), isoprenaline, adrenaline and the beta 2-adrenoceptor agonist, salbutamol, concentration-dependently relaxed penile resistance arteries, while the relaxations to noradrenaline and dobutamine, which activate beta 1-adrenoceptors, were negligible. Isoprenaline-induced relaxations were not changed in the presence of the beta 1-antagonist, atenolol (10(-7)-10(-6) M), but competitively inhibited by the beta 2-adrenoceptor antagonist, butoxamine (10(-6)-10(-5) M). The present results indicate that stimulation of adrenergic nerves in horse penile resistance arteries releases noradrenaline, which induces vasoconstriction through a predominant activation of alpha 1-adrenoceptors, while postjunctional alpha 2-adrenoceptors apparently play a minor role. Functional beta 2-adrenoceptors are also present in these arteries.
authors.affiliation: Departamento de Fisiología, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain. US@farm.aau.dk
authors.forename: U
authors.initials: U
authors.lastname: Simonsen
authors.forename: D
authors.initials: D
authors.lastname: Prieto
authors.forename: M
authors.initials: M
authors.lastname: Hernández
authors.forename: I
authors.initials: I
authors.lastname: Sáenz de Tejada
authors.forename: A
authors.initials: A
authors.lastname: García-Sacristán
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004730:Endothelium, Vascular / Q000502:physiology; D006736:Horses; D008297:Male; D009569:Nitric Oxide / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology*; D010413:Penis / Q000098:blood supply*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D015398:Signal Transduction; D014655:Vascular Resistance; D014661:Vasoconstriction
chemical_list: D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D009569:Nitric Oxide; D009638:Norepinephrine