ASSESSMENT OF MYELOPEROXIDASE ACTIVITY IN RENAL TISSUE AFTER ISCHAEMIA REPERFUSION/

We have shown that a photometric assay of myeloperoxidase derived from rat blood polymorphonucleocytes employing 3,3',5,5'-tetramethylbenzid ine as substrate is more sensitive than an established assay employing o-dianisidine. We went on to demonstrate that rat renal tissue is cap able of inhibiting peroxidase activity. This activity approached 100% when the rat renal supernate was incubated at 60 degrees C for 2 h and the assay was conducted in the presence of a 10-fold higher concentra tion of hydrogen peroxide (H2O2). Rat kidneys undergoing 45 min ischae mia and 1, 3 and 6 h reperfusion in vivo, exhibited significant increa ses in myeloperoxidase activity, indicating tissue polymorphonucleocyt e accumulation. Monoclonal antibodies against rat intercellular adhesi on molecule 1 (ICAM-1) and CD18 of beta(2),-integrins administered bot h 5 min before a period of 45 min renal ischaemia (20 mu g/kg i.v.) an d at the commencement of 1 h reperfusion (20 mu g/kg i.v.) reduced ren al tissue polymorphonucleocyte accumulation. However, similar treatmen t with the parent murine antibody immunoglobulin G1 (IgG1) and an unre lated murine antibody, IgG2a, also significantly reduced renal tissue polymorphonucleocyte accumulation. In conclusion, we demonstrate that the rat renal suppression of peroxidase activity can be overcome by a combination of heat inactivation and the provision of excess assay H2O 2. In addition, the available evidence suggests that murine monoclonal antibodies against rat adhesion molecules may exert non-specific acti ons in our model of renal ischaemia/ reperfusion in vivo.