Norepinephrine-induced contraction of isolated rabbit bronchial artery: role of alpha 1- and alpha 2-adrenoceptor activation.
The contractile effect of norepinephrine (NE) on isolated rabbit bronchial artery rings (150-300 microns in diameter) and the role of alpha 1- and alpha 2-adrenoceptors (AR) on smooth muscle and endothelium were studied. In intact arteries, NE increased tension in a dose-dependent manner, and the sensitivity for NE was further increased in the absence of endothelium. In intact but not in endothelium-denuded arteries, the response to NE was increased in the presence of both indomethacin (Indo; cyclooxygenase inhibitor) and NG-nitro-L-arginine methyl ester [L-NAME; nitric oxide (NO) synthase inhibitor], indicating that two endothelium-derived factors, NO and a prostanoid, modulate the NE-induced contraction. The alpha 1-AR antagonist prazosin shifted the NE dose-response curve to the right, and phenylephrine (alpha 1-AR agonist) induced a dose-dependent contraction that was potentiated by L-NAME or removal of the endothelium. The sensitivity to NE was increased slightly by the alpha 2-AR antagonists yohimbine and idazoxan, and this effect was abolished by Indo or removal of the endothelium. Similarly, contractions induced by UK-14304 (alpha 2-AR agonist) were potentiated by Indo or removal of the endothelium. These results suggest that NE-induced contraction is mediated through activation of alpha 1- and alpha 2-ARs on both smooth muscle and endothelium. Activation of the alpha 1- and alpha 2-ARs on the smooth muscle causes contraction, whereas activation of the endothelial alpha 1- and alpha 2-ARs induces relaxation through release of NO (alpha 1-ARs) and a prostanoid (alpha 2-ARs).
Zschauer
A O
AO
Division of Pulmonary and Critical Care Medicine, Mount Sinai Medical Center, University of Miami School of Medicine, Miami Beach, Florida 33140, USA.
Sielczak
M W
MW
Smith
D A
DA
Wanner
A
A
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D001980:Bronchi / Q000098:blood supply*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology*; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D011942:Receptors, Adrenergic, alpha; D014662:Vasoconstrictor Agents; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine; D007213:Indomethacin