Role of bradykinin in the vascular permeability response induced by carrageenin in rats

1 Bradykinin in carrageenin-induced inflammatory pouch fluid was measured by an enzyme immunoassay method. 2 The bradykinin showed a single peak in the 30-60 min period after the challenge and then decreased quickly, and there was a correlation between the bradykinin level and exudation of fluorescein-labelled bovine serum albumin in the first 60 min period. 3 Captopril (an inhibitor of kininase II) elevated both the bradykinin level in the inflammatory pouch fluid and vascular permeability, while DL-2-mercaptomethyl-3- guanidinoethylthiopropanoic acid (an inhibitor of kininase I) had no effect. 4 Soybean trypsin inhibitor (SBTI) inhibited the vascular permeability response in parallel with the decrease in the bradykinin level. 5 A bradykinin-degrading activity appeared in the pouch fluid within 1 h after the challenge and increased with time. 6 In the period of 3.5-4 h, bradykinin levels were suppressed below the sensitivity limit of the assay, i.e. 0.07 nm ml-1, in spite of active generation. This was because degradation of bradykinin was very rapid in this late stage. Nevertheless, bradykinin still played a definite role in sustaining a high level of vascular permeability response in the late stage in conjunction with prostaglandins.