COMPARISON OF CYCLIC-GMP IN HUMAN INTERNAL MAMMARY ARTERY AND SAPHENOUS-VEIN - IMPLICATIONS FOR CORONARY-ARTERY BYPASS GRAFT PATENCY

Objective: The aim was to examine the capacity of the human saphenous vein (native and surgically prepared) and the internal mammary artery to generate cyclic GMP, the second messenger that mediates smooth muscle relaxation following production of nitric oxide. Methods: 209 vessel segments were used from 22 patients undergoing coronary revascularisation. Isolated vessel segments were stimulated with a range of endothelium dependent and endothelium independent agonists and flash frozen for radioimmunoassay for cyclic GMP. Results: Control/basal levels of cyclic GMP were significantly higher in the internal mammary artery than either native or distended saphenous vein. Endothelium dependent agonist stimulation with acetylcholine, bradykinin, or substance P induced significant increases in cyclic GMP in internal mammary artery and native saphenous vein, whereas distended veins showed non-significant changes in response to agonist stimulation. Endothelium removal abolished agonist stimulated increases in cyclic GMP. Glyceryl trinitrate and sodium nitroprusside elicited significant further increases in cyclic GMP in native vein and internal mammary artery. All values obtained were significantly greater in arterial than in venous tissue. Conclusion: Differences in basal and stimulated cyclic GMP activity in arteries and veins have been shown. This could represent an additional protective mechanism against constrictor influences in arterial bypass grafts, which may explain their documented better long term performance.