title: Predominant alpha 1-adrenoceptor-mediated contraction in the human internal mammary artery.
abstract: alpha-Adrenoceptor agonists and antagonists are widely used perioperatively for internal mammary artery (IMA)-coronary artery bypass operations. To determine subtypes of alpha-adrenoceptors in the human IMA, we studied responses of isolated human IMA segments to alpha-adrenoceptor agonists, antagonists, and electrical stimulation in organ baths. The IMA ring segments (3 mm long) were set up at a physiologic and comparable condition according to their own length-tension curves. alpha 1-Agonist methoxamine (MO) induced 2.65 +/- 0.70 g force and alpha 1, alpha 2-agonist norepinephrine (NE) induced 4.07 +/- 0.70 g force. The contractions induced by both MO and NE were totally abolished by alpha 1-antagonist prazosin (0.1 microM) but not alpha 2-antagonist yohimbine. alpha 2-Agonist UK14304 induced only 0.39 +/- 0.17 g force, which was significantly less than that induced by MO or NE (p < 0.001). Contractions induced by electrical field stimulation (2, 10, 20 Hz) were decreased by alpha 1-antagonist prazosin 1 microM (p < 0.01) but potentiated by alpha 2-antagonist yohimbine. These results strongly suggest that in the human IMA the postjunctional alpha-adrenoceptors are predominantly of the alpha 1-subtype and therefore the alpha-adrenoceptor agonist-induced contraction and the sympathetic nerve stimulation-induced contraction is mediated mainly by activation of the alpha 1-adrenoceptors.
authors.affiliation: Cardiothoracic Surgical Unit, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: G W
authors.initials: GW
authors.lastname: He
authors.forename: J
authors.initials: J
authors.lastname: Shaw
authors.forename: C F
authors.initials: CF
authors.lastname: Hughes
authors.forename: C Q
authors.initials: CQ
authors.lastname: Yang
authors.forename: D S
authors.initials: DS
authors.lastname: Thomson
authors.forename: B
authors.initials: B
authors.lastname: McCaughan
authors.forename: P N
authors.initials: PN
authors.lastname: Hendle
authors.forename: D K
authors.initials: DK
authors.lastname: Baird
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008323:Mammary Arteries / Q000187:drug effects / Q000502:physiology; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha