Bradykinin (BK), kallidin (KD), & Substance P (SP) are hypotensive peptides that dilate & increase the permeability of capillaries. BK & KD have been implicated in the pathophysiology of septic and hemorrhagic shock, hemorrhagic pancreatitis, carcinoid syndrome, and post-gastrectomy dumping syndrome. Lung is an extremely important organ for BD and KD catabolism; site(s) and enzyme pathways (EP) for SP catabolism are less clear. Of at least six EP for BK and KD catabolism, only two (Kininase-I, EC 3.4.12.7; & Kininase-II, i.e., angiotensin converting enzyme, EC 3.4.15.1) have received significant study. Thus an important information gap exists now regarding at least four other EP that may have important BK & KD catabolism roles; these are an aminopeptidase-P, Kininase-III, EC 3.4.11.9; Post-Proline Cleaving Enzyme, EC 3.4.21.26; Dipeptidyl-Peptidase-IV, EC 3.4.14.5; and two endopeptidases which cleave the Phe5-Ser6 and Ser6-Pro7 BK bonds.
Our aims are (1) to isolate & characterize these enzymes from human lung, (2) to determine the relative quantitative importance of each of these six BK & KD catabolizing EP as compared to total BK and KD catabolism in lung in the absence & presence of Kininase-II inhibitors, (3) to determine the relative quantitative importance of these six EP and SP-Degrading Enzyme with respect to the total catabolism of SP in lung and other tissues. The concentration of each of these enzymes in lung and other tissues will be determined. Animal lung perfusion experiments will be done after the isolation and detailed characterization studies have been completed. In the perfusion experiments, lung will be perfused with balanced salts solution containing BK, KD, or SP, after which the amino acid and peptide fragments that appear in the resulting perfusate will be identified and assayed at several points in time after perfusion initiation; these results will allow calculation of the relative quantitative importance of each of the various EP with respect to total kinin or SP catabolism in lung. The perfusion experiments will be repeated with various interventions (captopril treatment, antibiotic treatment, hypoxemia, hypercapnia, acidosis) to assess their effect.
