title: Evidence for an inhibitory prejunctional P1-purinoceptor in the rat portal vein with characteristics of the A2 rather than of the A1 subtype.
abstract: The effects of adenosine (ADO) and of the adenosine analogues 5'-N-ethylcarboxamideadenosine (NECA), 2-chloroadenosine (2-CADO), L- and D-phenylisopropyladenosine (L- and D-PIA) and N6-cyclohexyladenosine (CHA) were compared on the contractile response of the isolated rat portal vein to perivascular adrenergic nerve stimulation. The order of potency at 20% inhibition of control values was NECA greater than or equal to 2-CADO = L-PIA greater than D-PIA = CHA greater than ADO. At this level of inhibition only D-PIA had a significant inhibitory effect against a matched concentration of exogenous NA. The difference in potency between L-PIA and D-PIA was approximately 3-fold. 8-Phenyltheophylline, a potent P1-purinoceptor antagonist, had a direct inhibitory effect on the tissue per se and therefore could not be used to antagonise these compounds. It is concluded that NECA, 2-CADO, L-PIA, D-PIA, CHA and ADO mediate their inhibitory effect in the rat portal vein via a prejunctional P1-purinoceptor which displays characteristics of the A2 classification, in contrast to that found to date in other adrenergic and cholinergic nerve terminals where it displays characteristics of the A1 classification.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011169:Portal Vein / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D011983:Receptors, Purinergic; D009435:Synaptic Transmission / Q000187:drug effects; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D013806:Theophylline; C028322:8-phenyltheophylline; D000241:Adenosine