STUDY OF THE VASODILATING ACTIVITY OF SALBUTAMOL ON DOG CORONARY-ARTERIES - UNEXPECTED EFFECTS OF METHYLENE-BLUE

The vascular relaxant effect of salbutamol and its dependence on the endothelium were studied in the isolated dog coronary artery, precontracted with prostaglandin F2-alpha. Salbutamol induced a concentration-dependent relaxation which was partially inhibited by removal of endothelial cells. Atenolol 10(-6) mol/l, a beta-1-selective antagonist, inhibited the relaxant effect of salbutamol both in the presence and in the absence of endothelium. Conversely, ICI 118,551 10(-6) mol/l, a beta-2-selective antagonist, antagonized the response to salbutamol only in intact vessels. Methylene blue amplified markedly the relaxation to salbutamol but only in denuded rings. Therefore, the vasodilating effect of salbutamol on large coronary arteries seems to result from the stimulation of both, beta-1-receptors on smooth muscle cells and beta-2-receptors on endothelial cells, demonstrating the existence of the two types of adrenoceptors in the wall of large dog coronary arteries. In addition, the effect obtained with methylene blue in this study shed some doubts on its specificity as a guanylate cyclase inhibitor.