title: Pre- and postjunctional alpha(2)-adrenergic receptors in fetal and adult ovine cerebral arteries.
abstract: In ovine cerebral arteries, adrenergic-mediated vasoconstrictor responses differ significantly with developmental age. We tested the hypothesis that, in part, these differences are a consequence of altered alpha(2)-adrenergic receptor (alpha(2)-AR) density and/or affinity. In fetal (approximately 140 days) and adult sheep, we measured alpha(2)-AR density and affinity with the antagonist [(3)H]idazoxan in main branch cerebral arteries and other vessels. We also quantified contractile responses in middle cerebral artery (MCA) to norepinephrine (NE) or phenylephrine in the presence of the alpha(2)-AR antagonists yohimbine and idazoxan and contractile responses to the alpha(2)-AR agonists clonidine and UK-14304. In fetal and adult cerebral artery homogenates, alpha(2)-AR density was 201 +/- 18 and 52 +/- 6 fmol/mg protein, respectively (P < 0.01); however, antagonist affinity values did not differ. In fetal, but not adult, MCA, 10(-7) M yohimbine significantly decreased the pD(2) for NE-induced tension in the presence of 3 x 10(-5) M cocaine, 10(-5) M deoxycorticosterone, and 10(-6) M tetrodotoxin. In fetal, but not adult, MCA, UK-14304 induced a significant decrease in pD(2) for the phenylephrine dose-response relation. In addition, stimulation-evoked fractional NE release was significantly greater in fetal than in adult cerebral arteries. In the presence of 10(-6) M idazoxan to block alpha(2)-AR-mediated inhibition of prejunctional NE release, the fractional NE release was significantly increased in both age groups. We conclude that in fetal and adult ovine cerebral arteries, alpha(2)-AR appear to be chiefly prejunctional. Nonetheless, the fetal cerebral arteries appear to have a significant component of postjunctional alpha(2)-AR.
authors: Center for Perinatal Biology, Department of Physiology, Loma Linda University School of Medicine, Loma Linda, California 92350, USA.
authors: John M
authors: JM
authors: Bishai
authors: Luit
authors: L
authors: Penninga
authors: Roel
authors: R
authors: Nijland
authors: Rogier
authors: R
authors: Meulenaar
authors: Ciprian P
authors: CP
authors: Gheorghe
authors: Yu
authors: Y
authors: Zhao
authors: John N
authors: JN
authors: Buchholz
authors: Lubo
authors: L
authors: Zhang
authors: Lawrence D
authors: LD
authors: Longo
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002536:Cerebral Arteries / Q000737:chemistry / Q000187:drug effects / Q000196:embryology / Q000378:metabolism*; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005333:Fetus; D019329:Idazoxan / Q000494:pharmacology; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011247:Pregnancy; D011810:Quinoxalines / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D012756:Sheep; D013779:Tetrodotoxin / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D015016:Yohimbine; D013779:Tetrodotoxin; D000068438:Brimonidine Tartrate; D003000:Clonidine; D009638:Norepinephrine; D019329:Idazoxan