Bradykinin receptor and tissue ACE binding in myocardial fibrosis: response to chronic angiotensin II or aldosterone administration in rats.

High density angiotensin converting enzyme (ACE) binding is present in the perivascular fibrosis involving intramyocardial coronary arteries and the microscopic scarring of the myocardium that accompanies chronic elevations in circulating angiotensin II (AngII) and/or aldosterone (ALDO). As a kininase II, ACE degrades bradykinin. Herein we sought to determine whether bradykinin (BK) receptor binding was associated with ACE binding in each of these experimental models. BK receptor binding was localized and quantified by in vitro quantitative autoradiography, using [125I-Tyr8]BK. In serial sections of the same heart hematoxylin and eosin (H&E) and picrosirius red (PSR) staining were utilized to address cardiac myocyte injury and fibrosis, respectively. Four experimental groups were examined: unoperated, untreated, age/sex matched controls: age/sex matched uninephrectomized control rats receiving a high sodium diet; animals that received AngII (9 micrograms/h sc) for 2, 4 or 6 weeks; and uninephrectomized rats on a high sodium diet that received ALDO (0.75 micrograms/h sc) for similar periods of time. We found: (a) myocardial fibrosis, including perivascular fibrosis and microscopic scarring, at week 2 of AngII, but not until week 4 or more of ALDO treatment; (b) low BK receptor binding in normal ventricles that was increased in scars and markedly increased in perivascular fibrosis at week 2 of AngII and each increased further at week 4 and 6 of AngII: (c) low BK receptor binding at week 2 and 4 weeks of ALDO treatment which became markedly increased at fibrous tissue sites at week 6. BK receptor and ACE binding were anatomically coincident and localized to each site of fibrosis in both models. The co-location of BK receptor and ACE binding in these models raises the prospect that fibrous tissue ACE may utilize BK as substrate and BK, in turn, may play a role in fibrous tissue formation.