Effect of the A2A-adenosine receptor agonist CGS 21680 on the evoked tritium overflow from isolated rat tail artery in α2-autoinhibition poor conditions. S1 and S2 are the overflows elicited by trains of 20 pulses at 50 Hz (pseudo-one-pulse stimulation; 30 min intervals between trains). CGS 21680 and/or UK 14304 (an α2-adrenoceptor agonist), CPA (an A1-receptor agonist) or 2-MeSATP (P2-receptor agonist) were added 5 min before S2. When tested alone, UK 14304, CPA and 2-MeSATP reduced tritium overflow (S2/S1 values between 32 and 65%, see text). Ordinate, S2/S1 values obtained in individual tissue preparations and expressed as percentage of the corresponding average control S2/S1 value. Values are means±s.e.mean from 7–12 tissue preparations. Significant differences from the appropriate control: *P<0.05 (unpaired Student's t-test).