Characterization of adenosine receptors in human pulmonary arteries

We have characterized the effects of adenosine, the A1-receptor agonist N6-(L-2-phenylisopropyl)-adenosine (PIA) and the A2-receptor agonist 5'-(N-ethyl)-carboxamido-adenosine (NECA), in isolated human pulmonary vessels. Fresh human lung tissue was obtained from nine patients, and small pulmonary arteries (200-400 micron ID) were dissected and mounted in an organ bath. The effects of the adenosine antagonist 8-phenyltheophylline (8-PT) and endothelial denudation were also studied. Adenosine, NECA, and PIA (1-300 microM) all caused a dose-dependent vasodilation with log EC30 values of -4.31, -4.31, and -3.53, respectively. 8-PT (10 microM) caused a rightward shift of the adenosine dose-response curve, significantly decreasing the effect of adenosine (pKB = 6.3). Mechanical removal of endothelial cells had no significant effect on adenosine-mediated vasodilation. We also compared the effects of adenosine on eight large (7-10 mm ID) and eight small (200-400 micron ID) arteries and found no significant difference in the sensitivity to adenosine between these vessels. Our findings suggest that the pulmonary vasodilator effects of adenosine in humans are mediated through A2 receptors that are localized to vascular smooth muscle. Adenosine may function as a regulator of pulmonary vascular tone in humans and may have therapeutic potential.