Adenosine: Differential effect on blood flow to subregions of the upper gastrointestinal tract

The potential of adenosine to regulate organ blood flow (ml/min/100 g tissue) in the intact rabbit upper alimentary tract was evaluated using the radioactive microsphere technique. Adenosine (1.0 μmole/kg/min) produced significant, greater than threefold increases in esophageal mucosal blood flow (37 ± 2 to 127 ± 47) and threefold increases in antral mucosal (39 ± 3 to 144 ± 24) and transmural small intestinal blood flow (duodenum, 60 ± 13 to 187 ± 22; jejunum, 42 ± 3 to 138 ± 16; ileum, 27 ± 2 to 80 ± 22). Inosine did not reproduce these effects. P₁-purinergic receptor antagonism with theophylline blocked the effects of adenosine. 5′-(N-Ethylcarboxamido)adenosine, an agonist of A₂-subtype, P₁-purinergic receptors, increased gastrointestinal organ blood flow similarly to adenosine with nmole/ kg/min doses. Similar doses of the A₁-subtype agonist, N⁵-cyclohexyladenosine, were ineffective, but μmole/kg/min doses produced small effects on esophageal mucosa and ileum. Our results indicate that in rabbit alimentary organs, adenosine preferentially increases blood flow to esophageal mucosa, antral mucosa, and small intestine. Its effects are mediated by the A₂-subtype of P₁-purinergic receptors.