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 m ost commonly used conduits for coronary artery bypass surgery (CABS). The ITA shows better long term patency than the SV, at least in part d ue to their different responses to agonists, as well as physical diffe rences between the ITA and SV at the time of grafting. 2 Angiotensin I I(A II), a potent endogenous vasoconstrictor circulates at augmented l evels 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 o n SV and ITA as intact rings from a heterogeneous group of patients un dergoing 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 funct ion of the endothelium in FSV, PSV and ITA, by measuring the relaxatio n of preconstricted rings to bradykinin. In some tissues endothelial p resence was examined histologically. 4 Surgical preparation of SV affe cted the contractile ability of the smooth muscle, as PSV contracted l ess 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, ove r the same concentration range (1 nM-100 nM). In rings of FSV the pres ence 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 response s 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 r elease was very small and unaffected by functional endothelium or by s urgical preparation. Stimulation with A II increased release only in r ings without functional endothelium, the increase in PSV rings being a bout 5 times that in FSV. 7 In conclusion, SV and ITA contract in a do se dependent manner to A II. However, they vary in their maximum respo nse, which is dependent upon the vessel type, surgical preparation and the presence of functional endothelium. 8 Further, surgical preparati on of SV does alter its behaviour by affecting the smooth muscle and e ndothelium of the vessel wall. The attenuation of contraction to A II seen in endothelialized FSV was not due to increased production of pro stacyclin by these rings and the differences seen between FSV and PSV cannot be attributed to prostacyclin release.