MECHANICAL-PROPERTIES AND EFFECTS OF SYMPATHETIC COTRANSMITTERS ON HUMAN CORONARY-ARTERIES AND VEINS

Active isometric wall tension was studied at different levels of passi ve wall tension in isolated circular 2 mm long segments of human epica rdial coronary arteries and veins, and maximum active wall tension was calculated to 6.60 mN/mm for arteries and 0.86 mN/mm for veins. Vasom otor responses to sympathetic co-transmitters were studied at resting tension and after precontraction with U46619. Noradrenaline (NA) and a denosine 5'-triphosphate (ATP) induced strong contractions of veins, w hereas relaxant responses dominated in arteries. Isoprenaline potently relaxed all arteries and veins. Prazosin and rauwolscine in a concent ration of 10(-7) M both competitively antagonized NA-induced contracti on of arteries and veins. For uridine 5'-triphosphate (UTP), relaxant responses were demonstrated in most arteries but only some veins. Neur opeptide Y (NPY) elicited no observable vasomotor responses in either arteries or veins. Mechanical removal of the arterial endothelium did not significantly alter relaxant responses to NA, ATP, UTP or isoprena line. In conclusion, alpha(1)- and alpha(2)-adrenoceptors mediating co ntraction and beta-adrenoceptors mediating relaxation seem to be prese nt in both human epicardial coronary arteries and veins. When applied to isolated epicardial coronary vessels, NA and ATP had a stronger inf luence on vasomotor tone than NPY and UTP, mediating strong contractio n of veins but mainly relaxation of coronary arteries, that was indepe ndent of an intact endothelium.