Figure 1.

Effect of the A_2A-adenosine receptor agonist CGS 21680 on the evoked tritium overflow from isolated rat tail artery in the absence of the α₂-adrenoceptor antagonist yohimbine (α₂-autoinhibition rich conditions: open circles, CGS 21680 alone; open squares, CGS 21680 in the presence of the A_2A-receptor antagonist ZM 241385) and in the presence of 1 μM yohimbine (α₂-autoinhibition poor conditions; filled circles). S₁ to S_n (S₂, S₃ and S₄) are the overflows elicited by trains of 100 pulses at 5 Hz (30 min intervals between trains). CGS 21680 was added, at increasing concentrations, 5 min before S₂, S₃ and S₄; ZM 241385 was added 20 min before S₄. When indicated, yohimbine was present throughout. Ordinate, S_n/S₁ values obtained in individual tissue preparations and expressed as percentage of the corresponding average control S_n/S₁ value. Values are means±s.e.mean from 7–20 tissue preparations. Significant differences from the appropriate control: *P<0.05 (unpaired Student's t-test); from CGS 21680 alone: #P<0.05 (ANOVA followed by Tukey's t-test).