LACK OF IMPORTANCE OF NO IN BETA-ADRENOCEPTOR-MEDIATED RELAXATION OF LARGE EPICARDIAL CANINE CORONARY-ARTERIES

This study was designed to test the role of endothelium and the L-argi nine/NO pathway in the relaxation of canine large coronary, arteries t o the beta-adrenoceptor agonist, isoprenaline. Relaxation of left circ umflex (LCX) and left anterior descending (LAD) coronary arteries were measured in organ baths after contraction with the thromboxane analog ue, U46619, either in absence or in presence of endothelium and in LCX arteries after pretreatment with N(G)-nitro-L-arginine-methyl-ester ( L-NAME). LAD arteries with and. without endothelium relaxed identicall y to isoprenaline but their maximal relaxation was smaller than corres ponding LCX arteries with endothelium. A slight but non significant di fference was observed in LCX arteries with endothelium as compared to rings without endothelium or pretreated with L-NAME. No difference was observed in the relaxation of LCX arteries to forskolin in arteries w ith or without endothelium. These results suggest that endothelium is not essential and that NO is not directly involved in the relaxation o f large coronary arteries induced by isoprenaline.