Age-related changes of bradykinin B1 and B2 receptors in rat heart.

Aging is a major risk factor for the development of vascular diseases, such as hypertension and atherosclerosis, that leads to end organ damage and especially heart failure. Bradykinin has been demonstrated to have a cardioprotective role by affecting metabolic processes and tissue perfusion under conditions of myocardial ischemia. Its actions are exerted via the bradykinin B1- and B2-type receptors (B1Rs and B2Rs), but the functional status of these receptors during the aging process is poorly understood. This study aims to investigate whether changes in B1R and B2R gene and protein expression in rat heart are associated with the age-related alterations of cardiac structure and function. Using real-time PCR, we found that B1R mRNA expression increased 2.9-fold in hearts of older rats (24 mo of age) compared with younger rats (3 mo of age), whereas B2R gene expression remained unchanged. Western blot analysis showed that expression of B2R at the protein level is approximately twofold higher in young rats compared with old rats, whereas the B1R protein is approximately twofold higher in old rats compared with young rats. The present results provide clear functional and molecular evidence that indicate age-related changes of bradykinin B1Rs and B2Rs in heart. Because the cardioprotective actions of bradykinin are physiologically mediated via the B2Rs, whereas the B1Rs become induced by tissue damage, these results suggest that age-related decreases in B2R protein levels may leave the heart vulnerable to ischemic damage, and increases in B1R expression and activity may represent a compensatory reaction in aging hearts.