ADENOSINE A(1) RECEPTORS ARE NOT INVOLVED IN CONTRACTION OF CANINE GASTRIC MUSCULARIS MUCOSAE BY ADENOSINE-ANALOGS

In vitro contractility studies were conducted in canine gastric muscul aris mucosae muscle strips with the adenosine analogues 2-chloroadenos ine (CIAD), 5'-N-ethylcarboxamidoadenosine (NECA), 5'-(N-cyclopropyl)- carboxamidoadenosine (CPCA), R-N-6-(2-phenylisopropyl)adenosine (R-PIA ), S-PIA, N-6-cyclohexyladenosine (S-PIA) and carboxyethyl)phenylamino -5'-N-carboxamidoadenosine (CGS21680) as well as the A(1)-selective an tagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Adenosine analogu es contracted the muscle strips with the following rank order of poten cy: CPCA > NECA > CIAD > R-PIA > CHA > S-PIA > CGS21680. CPCA, R-PIA, and CHA were partial agonists.: At a concentration selective for adeno sine A(1) receptors (50 nM), DPCPX did not alter the concentration-res ponse curves to CIAD or CHA. However, at higher concentrations (1-10 m u M), DPCPX antagonized CIAD-mediated contractions in a competitive ma nner (pA(2) = 6.96; slope = 0.93). CIAD-mediated contraction was not a ltered by treatment of the muscle strips with tetrodotoxin (1 mu g/ml) or mepyramine (1 mu M). Our results indicate that adenosine A(1) rece ptors, nerves or mast cells are not involved in contraction of canine gastric muscularis mucosae by adenosine analogues.