Actions of adenosine on nitro blue tetrazolium deposition and surface pH during intestinal reperfusion injury

Mesenteric arteries supplying an intestinal segment were occluded for 5 minutes and then released. During reperfusion, two series of measurements were made with various substances topically applied to the extraluminal surface. In the first series, reduced nitro blue tetrazolium (NBT) was extracted from tissue and measured spectrophotometrically, as an index of oxidative damage. In the second series, mucosal and serosal surface pH was measured as an index of the functional ability to maintain ion gradients. In control conditions, NBT deposition averaged 55-63 micrograms/g tissue. After 60 and 120 minutes of reperfusion, NBT was elevated to 446-479 micrograms/g, which was approximately half as large as the NBT increment (846 micrograms/g) produced by a 15-minute application of xanthine plus xanthine oxidase to well-perfused tissue. As expected, NBT levels were significantly lower (299 micrograms/g) in tissue that was continuously suffused with superoxide dismutase (SOD) plus catalase (CAT) before occlusion and during reperfusion. Similar NBT levels (274 micrograms/g) were observed after reperfusion in animals that were fed a diet supplemented with the antioxidant vitamin E for 4-6 weeks. These observations affirm that some, but not all, NBT deposition after reperfusion can be attributed to oxyradicals. However, with exogenous adenosine (ADO) applied for the first 30 minutes after occlusion, NBT was elevated to 174 micrograms/g after 60 minutes, which was only half as large as the increment with SOD plus CAT, even though those substances were continuously applied. The opposite effect was produced by an ADO receptor antagonist, 8-phenyltheophylline; NBT was increased to 516 micrograms/g.(ABSTRACT TRUNCATED AT 250 WORDS)