title: (+-)-N6-endonorbornan-2-yl-9-methyladenine (N-0861) and its enantiomers: selective antagonists of A1-adenosine receptors in guinea pig isolated atria.
abstract: Adenosine and its metabolically stable analog 5'-N-ethylcarbox-amidoadenosine (NECA) induce negative inotropic, chronotropic and dromotrpic actions in the heart through activation of A1-adenosine receptors and relaxation of vascular smooth muscle through activation of A2-adenosine receptors. In vitro studies were carried out in order to determine the potency of the antagonist (+-)-N6-endonorbornan-2-yl-9-methyladenine (N-0861) and its two component enantiomers, WRC-0006(+) and WRC-0007(-), at the A1 receptors in the guinea pig atria and the A2 receptors in the guinea pig aorta. N-0861 competitively antagonized the negative inotropic responses induced by NECA in the eletrically paced left atrium (pKB = 6.24) and the negative chronotropic responses induced by NECA in the spontaneously beating right atrium (pKB = 6.29). WRC-0007 was 4-fold more potent (pKB = 6.51) than WRC-0006 (pKB = 5.86) at antagonizing the A1-adenosine receptors in the guinea pig left atrium. N-0861, WRC-0007 and WRC-0006 at high concentrations (> 3 x 10(-5) M) produced direct relaxations of the guinea pig aorta that masked to a small extent the A2 receptor antagonism by these compounds. The affinities of the antagonists for the A2 receptor in the aorta were calculated using the method of pharmacological resultant analysis. N-0861 was 47-fold less potent at the A2 receptor (pKB = 4.57) than it was at the A1 receptor. WRC-0006 was 2-fold more potent (pKB = 4.81) than WRC-0007 (pKB = 4.52) at the A2-adenosine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Pharmacology, Whitby Research Inc., Richmond, Virginia.
authors: P L
authors: PL
authors: Martin
authors: A A
authors: AA
authors: Potts
authors: A M
authors: AM
authors: Sykes
authors: D G
authors: DG
authors: McKenna
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D004336:Drug Antagonism; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation; D009636:Norbornanes / Q000494:pharmacology*; D058914:Purinergic Antagonists; D013237:Stereoisomerism; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D009636:Norbornanes; D058914:Purinergic Antagonists; D014665:Vasodilator Agents; C073387:N 0861; D019830:Adenosine-5'-(N-ethylcarboxamide); D000225:Adenine; D000241:Adenosine