Adenosine is a vasodilator in the intestinal mucosa

The vasoactivity of adenosine in the intestinal mucosa of anesthetized dogs was determined using two experimental techniques. By use of the microsphere technique, infusion of adenosine (1 mumol/min ia) was found to increase significantly venous outflow and mucosal and muscularis blood flows in both jejunum (+77, +72, and +78%) and ileum (+111, +146, and +71%). In constant flow jejunal preparations, intra-arterial adenosine significantly decreased perfusion pressure (-32%), an index of vascular resistance, but did not significantly alter the blood flow distribution between the mucosa and muscularis as determined by microspheres. Thus adenosine equally dilated the mucosal and muscularis vasculatures. Using the second experimental technique, we found that local mucosal application of adenosine or non-metabolizable adenosine analogues [N6-cyclohexyladenosine or 5'-(N-ethylcarboxamido)-adenosine] dose dependently increased jejunal venous outflow. Almost all of the adenosine absorbed from the lumen was localized in the mucosal tissue, suggesting that the above hyperemia resulted from exposure of the mucosal vasculature to these compounds. The hyperemia produced by the luminal placement was not mediated by stimulation of the mucosal nerves, because the hyperemia was unaltered after treating the mucosal surface with a local anesthetic. The present results demonstrate therefore that adenosine is a vasodilator in the canine intestinal mucosa.