Role of bradykinin in renoprotective effects by angiotensin II type 1 receptor antagonist in salt-sensitive hypertension

To elucidate whether bradykinin is involved in the renoprotective effect produced by angiotensin II type 1 receptor antagonist (AT1A) in chronic salt-sensitive hypertension, Dahl salt-sensitive rats receiving a high-salt (8%) diet were treated either with an AT1A (candesartan, 1 mg/kg/day), a bradykinin B2 receptor antagonist (BKB2A; FR172357, 30 mg/kg/day) or a combination of AT1A and BKB2A for 7 weeks. None of the treatments changed the markedly increased systolic blood pressure induced by a high-salt diet. However, chronic treatment with AT1A significantly improved the histological hallmarks of renal damage-i.e., glomerular sclerosis and cell proliferation-despite the presence of severe hypertension. This beneficial action of AT1A was abolished by the concomitant administration of BKB2A. In agreement with these histologically based findings, increases in levels of creatinine clearance induced by AT1A were also reversed back to the basal levels when BKB2A was administered in conjunction with AT1A. Furthermore, urinary excretions of nitrate plus nitrite and prostaglandin E-2 increased moderately in response to the administration of AT1A alone, but not in combination with BKB2A. Thus, the blockade of bradykinin signaling abrogates the renoprotective actions of the angiotensin II type 1 (AT1) receptor antagonism. Collectively, these data show that when AT1 action is chronically blocked, endogenous bradykinin plays a pivotal role in preventing the progression of glomerular injury in salt-sensitive hypertension.