Peroxidase activity as a measure of neutrophil populations in inflammatoryperitoneal exudates of rainbow trout, Oncorhynchus mykiss (Walbaum)

A quantitative peroxidase assay using tetramethylbenzidine was applied to e xudates from peritoneal cavities of rainbow trout which had been inflamed b y intraperitoneal injection of Yersinia ruckeri. Most of the peroxidase act ivity was cell-associated, with values for extracellular peroxidase below 5 % of total peroxidase. No free peroxidase activity was detected in resting cavities. The kinetics of neutrophil numbers and peroxidase activity in per itoneal exudates during the 6 days of inflammation studied followed identic al patterns, with a correlation coefficient of 0.996. This shows that the p eroxidase assay can be used as an indirect, quantitative evaluation of neut rophil responses during peritoneal inflammation.