Effect of some vasodilators on cat femoral arteries

Adenosine, cyclic-AMP (cAMP), papaverine and 1-methyl-3-isobutylxanthine (MIX) evoked dose-dependent vasodilatation in cat femoral arteries precontracted with 75 mM K+. The vasodilator response induced at maximal concentration used was: papaverine greater than MIX greater than adenosine = cAMP. With regard to the potency of relaxant effects (IC10) the order was MIX = cAMP = papaverine greater than adenosine. The dilatation elicited by papaverine, adenosine and cAMP was increased by MIX. Preincubation with adenosine enhanced the relaxation induced by MIX and reduced that produced by cAMP. These results indicate that the effects of adenosine and cAMP seem not to be mediated by specific surface receptors but by a cAMP-dependent mechanism. The interference between adenosine and cAMP could be due to competition for a similar site and/or mechanism.