The dilatatory action of adenosine on pial arteries of cats and its inhibition by theophylline.

The effect of adenosine upon pial resistance vessels was studied using local microapplication from the perivascular side and measurement of vascular diameter. Concentration-response curves revealed a concentration-dependent dilatatory effect of adenosine between 10(-7) and 10(-3) M. The degree of dilatation was independent of initial vessel size (47-260 mu). The dilatations due to adenosine could be reduced by theophylline in a reversible competitive antagonism. Concentration-response curves for theophylline yielded no vascular reaction at concentrations of up to 10(-5) M theophylline. From these data is is concluded that the pial arterial resting tone is not influenced under our experimental conditions by adenosine formed and released by brain tissue. The dilatations measured at high theophylline concentrations are apparently due to a mechanism different from the adenosine antagonism.