Involvement of superoxide in acute reaction of angiotensin II in mesenteric microcirculation

Superfusion of angiotensin II (Ang It) ceased blood flow in rat mesenteric microcirculation, however, successive reflow occurred. When nitric oxide sy nthase inhibitor was present, the stoppage of flow occurred by the lower co ncentration of Ang II. Superoxide dismutase (SOD) significantly delayed the stoppage by Ang II and restored the successive reflow earlier. The acute r eaction between Ang II and mesenteric artery induced immediate superoxide ( . O-2(-)) production when observed by a chemiluminescence method using the Cypridina luciferin analog. The acute vascular . O-2(-) production On the a ddition of Ang II contributed to in vitro vascular contraction as it was si gnificantly attenuated by SOD. The acute superoxide-producing effect is lik ely to be specific to Ang Il because such significant modification by SOD w as not observed for norepinephrine.