HALOTHANE INHIBITION OF ACETYLCHOLINE-INDUCED RELAXATION IN RAT MESENTERIC-ARTERY AND AORTA

Purpose: The effect of halothane was compared on acetylcholine (ACh)-i nduced relaxation of the mesenteric artery acid the aorta in rats. Met hods: The responses of isolated rat aortic and mesenteric arterial rin g segments precontracted with phenylephrine to ACh (10(-8)-10(-5) M), in the presence of halothane 0-3%, were compared using isometric force tension recordings, Effects of N-G-nitro-1-arginine (L-NOARG, 3 x 10( -5)), methylene blue (MB, 5 x 10(-6) M), oxyhaemoglobin (OxyHB, 10(-7) M), and various potassium channel inhibitors; tetraethylammonium (TEA , 10(-5) M, 10(-3) M), apamin (AP, 10(-7) M), charybdotoxin (ChTx, 10( -7) M) and glibendamibe (GC, 10(-5) M) on ACh-induced relaxation in me senteric artery were tested, Using radioimmunoassay, ACh (10(-6) M)-in duced guanosine 3':5'-cyclic monophosphate (cGMP) accumulation of mese nteric arterial rings pretreated with L-NAORG were also measured. Resu lts: L-NOARG partially inhibited ACh-induced region in mesenteric arte rial rings (P < 0.05, maximum relaxation reduced by approximately 50%) , whereas it abolished them in aortic rings. The remaining relaxation resistant to L-NOARG in mesenteric arterial rings was insensitive-to a dditional MB or OxyHB, and was not accompanied by increases in cGMP co ntents of rings. Halothane inhibited endothelium-dependent relaxation in aorta and mesenteric arterial rings, This inhibitory effect was lar ger in aorta, Halothane also inhibited NO independent EDHF-dependent r elaxation in the mesenteric arterial rings. Conclusion: Despite a simi lar inhibitory effect on the EDHF relaxing pathway, halothane has a la rger effect on endothelium-dependent relaxation in the aorta (NO depen dent mainly) than in mesenteric rings (NO and EDHF dependent).