Abstract-We evaluated the development of arterial hypertension, cardiac function, and collagen deposition, as well as the level of components of the renin-angiotensin system in the heart of transgenic rats that overexpress an angiotensin (Ang)-(1-7)-producing fusion protein, TGR(A1-7)3292 (TG), which induces a lifetime increase in circulating levels of this peptide. After 30 days of the induction of the deoxycorticosterone acetate (DOCA)-salt hypertension model, DOCA-TG rats were hypertensive but presented a lower systolic arterial pressure in comparison with DOCA-SpragueDawley (SD) rats. In contrast to DOCA-SD rats that presented left ventricle (LV) hypertrophy and diastolic dysfunction, DOCA-TG rats did not develop cardiac hypertrophy or changes in ventricular function. In addition, DOCA-TG rats showed attenuation in mRNA expression for collagen type I and III compared with the increased levels of DOCA-SD rats. Ang II plasma and LV levels were reduced in SD and TG hypertensive rats in comparison with normotensive animals. DOCA-TG rats presented a reduction in plasma Ang-(1-7) levels; however, there was a great increase in Ang-(1-7) (Ϸ3-fold) accompanied by a decrease in mRNA expression of both angiotensin-converting enzyme and angiotensin-converting enzyme 2 in the LV. The mRNA expression of Mas and Ang II type 1 receptors in the LV was not significantly changed in DOCA-SD or DOCA-TG rats. This study showed that TG rats with increased circulating levels of Ang-(1-7) are protected against cardiac dysfunction and fibrosis and also present an attenuated increase in blood pressure after DOCA-salt hypertension. In addition, DOCA-TG rats showed an important local increase in Ang-(1-7) levels in the LV, which might have contributed to the attenuation of cardiac dysfunction and prefibrotic lesions. (Hypertension. 2010;55:889-896.)

Angiotensin-(ANG)-(1-7) is known by its central and peripheral actions, which mainly oppose the deleterious effects induced by accumulation of ANG II during pathophysiological conditions. In the present study we evaluated whether a chronic increase in ANG-(1-7) levels in the brain would modify the progression of hypertension. After DOCA-salt hypertension was induced for seven days, Sprague-Dawley rats were subjected to 14 days of intracerebroventricular (ICV) infusion of ANG-(1-7) (200 ng/h, DOCA-A7) or 0.9% sterile saline. As expected, on the 21st day, DOCA rats presented increased mean arterial pressure (MAP) (≈40%), and impaired baroreflex control of heart rate (HR) and baroreflex renal sympathetic nerve activity (RSNA) in comparison with that in normotensive control rats (CTL). These changes were followed by an overactivity of the cardiac sympathetic tone and reduction of the cardiac parasympathetic tone, and exaggerated mRNA expression of collagen type I (≈9-fold) in the left ventricle. In contrast, DOCA rats treated with ANG-(1-7) ICV had an improvement of baroreflex control of HR, which was even higher than that in CTL, and a restoration of the baroreflex control of RSNA, the balance of cardiac autonomic tone, and normalized mRNA expression of collagen type I in the left ventricle. Furthermore, DOCA-A7 had MAP lowered significantly. These effects were not accompanied by significant circulating or cardiac changes in angiotensin levels. Taken together, our data show that chronic increase in ANG-(1-7) in the brain attenuates the development of DOCA-salt hypertension, highlighting the importance of this peptide in the brain for the treatment of cardiovascular diseases.

Abstract-Mineralocorticoids have been implicated in the pathogenesis of diastolic heart failure. On the contrary, angiotensin (Ang)-(1-7) has emerged as a potential strategy for treatment of cardiac dysfunction induced by excessive mineralocorticoid receptor activation. A critical question about the cardioprotective effect of Ang-(1-7) in hypertensive models is its dependence on blood pressure (BP) reduction. Here, we addressed this question by investigating the mechanisms involved in Ang-(1-7) cardioprotection against mineralocorticoid receptor activation. Sprague-Dawley (SD) and transgenic (TG) rats that overexpress an Ang-(1-7) producing fusion protein (TG(A1-7)3292) were treated with deoxycorticosterone acetate (DOCA) for 6 weeks. After treatment, SD rats became hypertensive and developed ventricular hypertrophy. These parameters were attenuated in TG-DOCA. SD-DOCA rats developed diastolic dysfunction which was associated at the cellular level with reduced Ca 2+ transient. Oppositely, TG-DOCA myocytes presented enhanced Ca 2+ transient. Moreover, higher extracellular signal-regulated kinase phosphorylation, type 1 phosphatase, and protein kinase Cα levels were found in SD-DOCA cells. In vivo, pressor effects of DOCA can contribute to the diastolic dysfunction, raising the question of whether protection in TG was a consequence of reduced BP. To address this issue, BP in SD-DOCA was kept at TG-DOCA level by giving hydralazine or by reducing the DOCA amount given to rats (Low-DOCA). Under similar BP, diastolic dysfunction and molecular changes were still evident in DOCA-hydralazine and SD-low-DOCA, but not in TG-DOCA. In conclusion, Ang-(1-7) protective signaling against DOCA-induced diastolic dysfunction occurs independently of BP attenuation and is mediated by the activation of pathways involved in Ca 2+ handling, hypertrophy, and survival.

In addition to the role of β‐arrestin in AT1 receptor second messenger desensitization, more recent evidence revealed that β‐arrestins act as scaffolds for numerous signaling networks, such as the MAPKs. On the other hand, Ang‐(1‐7) anti‐trophic effect in the cardiomyocytes can be mediated by alterations in the MAPKs pathways. In this study we evaluated the effect of AVE0991 (AVE), a nonpeptide Ang‐(1‐7) mimic, on the signaling pathways involved in the heart hypertrophy induced by DOCA‐salt hypertension (DSH). After 4 weeks of induction of DSH, rats received AVE (1mg/kg) by gavage for 2 weeks. AVE attenuated the DSH‐induced hypertrophy, as quantified by myocyte diameter measurements (Normotensive rats: 12.97±0.15 μm; DSH: 14.41±0.23 μm; DSH+AVE: 13.39±0.15 μm; n=3 each), without changing the increased blood pressure (tail cuff pletismography). DSH rats showed an increased mRNA expression (real time PCR) of β‐arrestin in the left ventricle (LV) (5.96±1.44 A.U. vs 1.01±0.07 A.U. in normotensive rats; p<0.05) that was blocked after AVE (0.84±0.13 A.U.). In addition, AVE induced an increased AT1 receptor expression in the LV (1.95±0.32 vs 1.01±0.09 in normotensive rats; p<0.05). No alteration in cardiac adenylate cyclase expression was observed. These data suggest that Ang‐(1‐7) may modulate DSH‐induced cardiac hypertrophy by altering the β‐arrestin pathway. Financial Support: CNPq and INCT

The present study evaluated the role of female sex hormones on the adverse effects of diabetes in cardiac function. Adult female Sprague‐Dawley rats (10 weeks‐old) were submitted to ovariectomy. One week later, diabetes was induced with a single dose of streptozotocin (65 mg/kg, i.p) without insulin replacement. After 4 weeks cardiac function was evaluated by echocardiography (Vevo 2100, VisualSonics, Toronto, Ontario, Canada) in intact controls (CTL); diabetics (STZ); ovariectomized (OVX); and OVX with diabetes (OVX‐STZ). Diabetes and OVX alone or in combination did not affect systolic blood pressure. While OVX animals exhibited a higher LV weight: tibia length ratio (LVW/TL; 18%; vs CTL; p<0.05), LVW/TL was particularly reduced in the diabetic animals (STZ: 14%; OVX‐STZ: 11%; vs CTL; p<0.05). However, the relative wall thickness was decreased in OVX and diabetic animals (STZ: 21%; OVX: 18%; OVX‐STZ: 21%; vs CTL; p<0.05). The ejection fraction (EF) and fractional shortening (FS) were decreased in OVX, respectively (65% ± 1% vs 72 % ± 2% in CTL; 37± 1% vs 43 ± 2% in CTL). The systolic function was markedly reduced by the same magnitude in both STZ (EF: 66± 1%; FS: 38 % ± 1%) and OVX‐STZ (EF: 65± 2%; FS: 37± 1%) relative to CTL. These data indicate that diabetes removes the cardioprotective effect of estrogen on cardiac function independently of alterations in blood pressure.