Circumferential stretching of saphenous vein smooth muscle enhances vasoconstrictor responses by Rho kinase-dependent pathways

Surgical preparation and/or pulsatile arterial perfusion of saphenous vein increases the sensitivity of vein rings to calcium mobilising agonists such as phenylephrine. We have investigated the mechanism(s) underlying this effect. We have used an ex vivo flow circuit, with simulated arterial or venous flows (mean pressure 100 and 20 mmHg, respectively), to investigate the sensitivity of human saphenous vein to phenylephrine, 5-hydroxytryptamine (5-HT) and KCl, using organ chamber pharmacology. After 90 min of pulsatile arterial perfusion the mean maximum tension induced by KCl had increased from 4.7 to 11.1 g (n=5), by phenylephrine had increased from 4.4 to 10.2 g (n=8) and by 5-HT had increased from 4.4 to 6.7 g (n=10), all P