Influence of adenosine and lowered cerebral blood flow on the cerebrovascular efefct of theophylline

Abstract The responses of brain vessels to theophylline infused intra-arterially was evaluated. The experiments were performed on isolated canine brains perfused by donor dogs. Thus secondary effects due to theophyline were eliminated. Arterial pO 2 , pCO 2 , pH and brain temperature were kept constant. Cerebral vascular resistance (CVR) was calculated from total venous outflow and cerebral perfusion pressure. A 2 mg doses of theophylline per brain was given at normal cerebral perfusion pressure (about 81 mm Hg), at lowered perfusion pressure (about 37 mm Hg), and during and adenosine infusion lasting 10 min (10 −7 mol/min). At normal pressure theophylline showed a significant 15% decrease of CVR, but at lowered perfusion pressure a significant 19% increase occured. During infusion of adenosine, which decreased CVR by 23%, theophylline again increased CVR by 20% thus demonstrating an edonosine-theophylline antagonism. From our results, it is suggested that adenosine could be involved in the vasodilatation of cerebral vessels in the hypoxic brain.