The present studies were conducted to determine whether des-Arg-kinins can produce relaxation of isolated vessels. Both des-Arg9-bradykinin and bradykinin produced dose-dependent relaxations of isolated rabbit superior mesenteric arteries. Des-Arg9-bradykinin (ED50 = 7.2 X 10(-9) M) was 8.5 times more potent than bradykinin (ED50 = 6.1 X 10(-8) M). Des-Arg9-bradykinin-mediated relaxation was inhibited by the specific B1 receptor antagonist [Leu8]des-Arg9-bradykinin which produced parallel shifts in the dose-response curve. Schild regression analysis of the data established a pA2 value (6.46) similar to that reported for B1 receptor-mediated contraction. Although the relaxant effect of bradykinin was also inhibited by the B1 antagonist, parallel shifts in the dose response curve were not produced. Relaxation of the mesenteric artery by both des-Arg9-bradykinin and bradykinin was inhibited by the cyclooxygenase inhibitor indomethacin. The results of these studies indicate that in addition to vasoconstriction, des-Arg9-bradykinin can produce vasorelaxation which may be mediated through stimulation of B1 kinin receptors and the subsequent release of prostaglandins.