THE EVIDENCE FOR HISTAMINE H-3 RECEPTOR-MEDIATED ENDOTHELIUM-DEPENDENT RELAXATION IN ISOLATED RAT AORTA

THE presence of histamine H-3 receptors was evaluated on the mt aorta endothelium. In the presence of pyrilamine (1nM, 7nM, 10nM) or thioperamide (1nM, 10nM, 30nM) the concentration-response awe for histamine-induced (0.1nM-0.01mM) endothelium-dependent rat aorta relaxation was shifted to the right without significant change of the E(max) indicating competitive antagonism by pyrilamine (pA(2)=9.33+/-0.34, slope=1.09+/-0.36) or thioperamide (pA(2)=9.31+/-0.16, slope=0.94+/-0.10). Cimetidine (1 mu M) did not influence histamine-induced endothelium-dependent rat aorta relaxation. In the presence of thioperamide (1nM, 10nM, 30nM) the concentration-response curve for (R)alpha-MeHA-induced (0.1nM-0.01mM) endothelium-dependent relaxation was shifted to the right without significant change of E(max) indicated competitive antagonism by thioperamide (pA(2)=9.21+/-0.4, slope=1.03+/-0.35). Pyrilamine (100nM) or cimetidine (1 mu M) did not influence (R)alpha-MeHA-induced endothelium-dependent rat aorta relaxation. These results suggest the presence of a heterogenous population of histamine receptors, H-1 and H-3, On Tat aorta endothelium.