Angiotensin type 1a receptor-deficient mice develop diabetes-induced cardiac dysfunction, which is prevented by renin-angiotensin system inhibitors

Background: Diabetes-induced organ damage is significantly associated with the activation of the renin-angiotensin system (RAS). Recently, several studies have demonstrated a change in the RAS from an extracellular to an intracellular system, in several cell types, in response to high ambient glucose levels. In cardiac myocytes, intracellular angiotensin (ANG) II synthesis and actions are ACE and AT(1) independent, respectively. However, a role of this system in diabetes-induced organ damage is not clear. Methods: To determine a role of the intracellular ANG II in diabetic cardiomyopathy, we induced diabetes using streptozotocin in AT(1a) receptor deficient (AT(1a)-KO) mice to exclude any effects of extracellular ANG II. Further, diabetic animals were treated with a renin inhibitor aliskiren, an ACE inhibitor benazeprilat, and an AT(1) receptor blocker valsartan. Results: AT(1a)-KO mice developed significant diastolic and systolic dysfunction following 10 wks of diabetes, as determined by echocardiography. All three drugs prevented the development of cardiac dysfunction in these animals, without affecting blood pressure or glucose levels. A significant down regulation of components of the kallikrein-kinin system (KKS) was observed in diabetic animals, which was largely prevented by benazeprilat and valsartan, while aliskiren normalized kininogen expression. Conclusions: These data indicated that the AT(1a) receptor, thus extracellular ANG II, are not required for the development of diabetic cardiomyopathy. The KKS might contribute to the beneficial effects of benazeprilat and valsartan in diabetic cardiomyopathy. A role of intracellular ANG II is suggested by the inhibitory effects of aliskiren, which needs confirmation in future studies.