INFLUENCE OF ENDOTHELIUM AND SURGICAL PREPARATION ON RESPONSES OF HUMAN SAPHENOUS-VEIN AND INTERNAL THORACIC ARTERY TO ANGIOTENSIN-II

1 The saphenous vein (SV) and internal thoracic artery (ITA) are the most commonly used conduits for coronary artery bypass surgery (CABS). The ITA shows better long term patency than the SV, at least in part due to their different responses to agonists, as well as physical differences between the ITA and SV at the time of grafting. 2 Angiotensin II(A II), a potent endogenous vasoconstrictor circulates at augmented levels during and after CABS, but little is known about the effects of A II on the SV and ITA. 3 We studied the contractile effects of A II on SV and ITA as intact rings from a heterogeneous group of patients undergoing CABS. Two groups of SV samples were studied; freshly excised SV (FSV) with no further manipulation and SV that had been surgically prepared for use as a bypass conduit (PSV). We also assessed the function of the endothelium in FSV, PSV and ITA, by measuring the relaxation of preconstricted rings to bradykinin. In some tissues endothelial presence was examined histologically. 4 Surgical preparation of SV affected the contractile ability of the smooth muscle, as PSV contracted less than FSV to potassium chloride (KCl, 90 mM) (P < 0.0001). Loss of endothelial function was seen in 25% of FSV, 50% of PSV and 33% of ITA. 5 A II caused concentration dependent contractions in all rings, over the same concentration range (1 nM-100 nM). In rings of FSV the presence of functional endothelium attenuated the response, median values with endothelium being less than half that without endothelium (P < 0.0007, at 100 nM). In rings of PSV responses to A II were unaffected by endothelial function, as were responses in rings of ITA. The responses of ITA were generally lower than the SV, both in absolute terms (mN) and when expressed as percentages of the responses to KCl. 6 Release of prostacyclin from SV was measured under various conditions. Basal release was very small and unaffected by functional endothelium or by surgical preparation. Stimulation with A II increased release only in rings without functional endothelium, the increase in PSV rings being about 5 times that in FSV. 7 In conclusion, SV and ITA contract in a dose dependent manner to A II. However, they vary in their maximum response, which is dependent upon the vessel type, surgical preparation and the presence of functional endothelium. 8 Further, surgical preparation of SV does alter its behaviour by affecting the smooth muscle and endothelium of the vessel wall. The attenuation of contraction to A II seen in endothelialized FSV was not due to increased production of prostacyclin by these rings and the differences seen between FSV and PSV cannot be attributed to prostacyclin release.