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

Objective: 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. Methods: 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. Results: 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<0.01. Phenylephrine did not augment the tension in vein rings maximally precontracted with KCl (n=4). The EC50 for KCl was unchanged after pulsatile arterial perfusion (n=5), but for phenylephrine and 5-HT there were significant reductions from 14±5 to 2±1 µM (n=8) and from 1.0±0.4 to 0.20±0.06 µM (n=10), respectively. The rate of contraction (in response to 3 µM phenylephrine) increased from 0.11 g/min to 0.37 g/min, P<0.02, after arterial perfusion (n=4). These changes in contractile properties (to phenylephrine) were endothelium-independent, evident within 5 min of simulated arterial perfusion. The changes in contractile properties could be abrogated by external stenting of the vein (to attenuate circumferential deformation) or inclusion in the perfusate of a vasodilator, e.g., cromakalim (5 µM) or the selective Rho kinase inhibitor Y-27632 (20 µM). The heightened sensitivity and contractility to phenylephrine was maintained after inclusion of adenosine (100 µM), gadolinium (10 µM) or cycloheximide (10 µM) in the vein perfusate. Conclusions: The circumferential deformations imposed by simulated arterial perfusion alter the vasomotor responses of saphenous vein smooth muscle. These effects are independent of new protein synthesis or the activation of stretch activated cation channels. The Rho kinase pathway appears to mediate the signalling mechanisms leading to increased agonist-induced tension and the increased sensitivity to vasoconstrictors. © 2002 Elsevier Science B.V. All rights reserved.