Background: Bradykinin is a potent cardioprotective hormone, the beneficial role of which in vivo appears to be limited by its rapid metabolism. Inhibitors of peptidases that degrade endogenously formed bradykinin are themselves cardioprotective, presumably by increasing local bradykinin concentrations. As bradykinin-degrading peptidases are potential therapeutic targets, it is important to identify these enzymes in different animal models of cardiac function.
Objective: To determine the mechanism of bradykinin degradation in the coronary circulation of the rabbit, using an isolated perfused heart preparation.
Design and methods: [3H]Bradykinin (16 nmol/l) was perfused as a bolus through the isolated rabbit heart in the presence and absence of specific peptidase inhibitors. The effluent was collected and the radiolabeled metabolites of [3H]bradykinin were separated by high performance liquid chromatography, identified, and quantified.
Results: [3H]Bradykinin was metabolized to the extent of 62 +/- 3% in a single passage through the rabbit coronary circulation at a physiological flow rate. The metabolites were identified as [3H]bradykinin(1-5) and [3H]bradykinin(1-7),accounting for 50 +/- 4 and 12 +/- 2% of the radioactivity, respectively. Co-perfusion with the angiotensin converting enzyme inhibitor, ramiprilat, completely blocked formation of these metabolites.
Conclusions: Angiotensin-converting enzyme fully accounts for the metabolism of [3H]bradykinin in the rabbit coronary circulation. This result contrasts with data obtained using rat heart, which demonstrated a prominent role for aminopeptidase P in bradykinin metabolism in this species.