Extracellular nucleotides induce vasodilatation in human arteries via prostaglandins, nitric oxide and endothelium‐derived hyperpolarising factor

The present study was aimed at examining P2 receptor‐mediated vasodilatation in human vessels. The isometric tension was recorded in isolated segments of the human left internal mammary artery branches precontracted with 1 μ M noradrenaline. Endothelial denudation abolished the dilator responses. The selective P2Y 1 agonist, 2‐MeSADP, induced a potent vasodilatation (pEC 50 =6.9±0.1). The P2Y 1 antagonist of 10 μ M , MRS 2216, shifted the 2‐MeSADP concentration‐response curve 1.1 log units to the right. The combined P2Y 1 and P2X agonist, 2‐MeSATP, stimulated a dilatation with a potency similar to that of 2‐MeSADP. Furthermore, MRS 2216 had a similar antagonistic effect on both 2‐MeSATP and 2‐MeSADP indicating that P2X receptors do not mediate vasodilatation. Both the P2Y 2/4 agonist, UTP γ S and the P2Y 6 agonist, UDP β S, stimulated potent dilatations (pEC 50 =7.8±0.4 for UTP γ S and 8.4±0.2 for UDP β S). The 2‐MeSADP‐induced nitric oxide (NO)‐mediated dilatation was studied in the presence of 10 μ M indomethacin, 50 n M charybdotoxin and 1 μ M apamin. The involvement of the endothelium‐derived hyperpolarising factor (EDHF) was investigated in the presence of 0.1 m M L ‐NOARG and indomethacin. The involvement of prostaglandins was investigated in the presence of L ‐NOARG, charybdotoxin and apamin. Both NO, EDHF and prostaglandins mediated 2‐MeSADP dilatation with similar efficacy ( E max =25±5% for NO, 25±6% for EDHF and 27±5% for prostaglandins). In conclusion, extracellular nucleotides induce endothelium‐derived vasodilatation in human vessels by stimulating P2Y 1 , P2Y 2/4 and P2Y 6 receptors, while P2X receptors are not involved. Endothelial P2Y receptors mediate dilatation by release of EDHF, NO and prostaglandins British Journal of Pharmacology (2003) 138 , 1451–1458. doi: 10.1038/sj.bjp.0705186