ENDOTHELIUM-DEPENDENT COMPONENT IN THE CONTRACTILE RESPONSES OF HUMANOMENTAL ARTERIES TO ADRENERGIC-STIMULATION

The present study was designed to investigate the influence of endothe lium-derived nitric oxide on the contractile responses of isolated hum an omental arteries to electrical field stimulation and noradrenaline. We measured isometric tension in artery rings obtained from portions of human omentum during the course of abdominal operations (32 patient s). Electrical field stimulation induced frequency-dependent contracti ons which were abolished by tetrodotoxin ( 10(-6) M) and prazosin (10( -6) M), thus indicating that this effect was due to noradrenaline rele ased from adrenergic nerves acting on alpha1-adrenoceptors. The increa ses in tension induced by electrical field stimulation were of greater magnitude in arteries denuded of endothelium. N(G)-Nitro-L-arginine ( L-NAME, 10(-4) M) potentiated the contractile response to electrical f ield stimulation in artery rings with endothelium but did not influenc e the contractile responses of endothelium-denuded arteries. The poten tiation induced by L-NAME was completely reversed by L-arginine (10(-4 ) M), but not by D-arginine 10(-4) M). Contractile responses to noradr enaline were similar in arteries with and without endothelium. L-NAME (10)-4) M) had no significant effect on the contractile responses to n oradrenaline. Our results suggest that electrical field stimulation re leases endothelium-derived nitric oxide which inhibits the contractile responses of human omental arteries. The constrictor responses to nor adrenaline are not modulated by the endothelium.