Training-Induced Deactivation of the AT1 Receptor Pathway Drives Autonomic Control and Heart Remodeling During the Transition From the Pre- to Hypertensive Phase in Spontaneously Hypertensive Rats.

BACKGROUND: The effects of hypertension and exercise training (T) on the sequential interplay between renin-angiotensin system (RAS), autonomic control and heart remodeling during the development of hypertension in spontaneously hypertensive rats (SHR), was evaluated.Methods and Results:Time course changes of these parameters were recorded in 4-week-old SHR submitted to a T or sedentary (S) protocol. Wistar Kyoto rats served as controls. Hemodynamic recordings were obtained in conscious rats at experimental weeks 0, 1, 2, 4, and 8. The left ventricle (LV) was collected to evaluate RAS gene and protein expression, cardiomyocytes' hypertrophy and collagen accumulation. Pre-hypertensive SHR exhibited augmented AT1R gene expression; at 5 weeks, they presented with elevated pressure, increased LV angiotensinogen and ACE mRNA expression, followed by sympathoexcitation (from the 8thweek onwards). Marked AT1R protein content, myocytes's hypertrophy, collagen deposition and increased pressure variability were observed in 12-week-old sedentary SHR. In addition to attenuating all these effects, T activated Mas receptor expression augmented parasympathetic modulation of the heart, and delayed the onset and reduced the magnitude, but did not block the development of genetic hypertension. CONCLUSIONS: The close temporal relationship between changes in the LV ACE-Ang II-AT1R axis, autonomic control and cardiac remodeling at both the establishment of hypertension and during exercise training reveals the essential role played by the AT1R pathway in driving cardiac remodeling and autonomic modulation during the transition from the pre- to hypertensive phase.

Proinflammatory Role of Angiotensin II in the Aorta of Normotensive Mice.

Angiotensin II plays important functions in cardiovascular system mediating actions leading to inflammatory responses such as activation of VSMC in order to produce ROS, inflammatory cytokines, chemokines, and adhesion molecules. Changes in angiotensin II production could stimulate the recruitment and activation of myeloid cells initiating local inflammatory response without effect on BP. We aimed to verify if angiotensin II induces an inflammatory response in the aorta and if it correlates with variations in BP. C57Bl/6 mice treated with saline solution (0.9%, control group) or angiotensin II (30ng/kg, Ang II group) were used. BP and HR levels were measured. Immunohistochemistry for IL1-ß, TGF-ß, iNOS, CD45, and α-actin was performed in the aorta. BP and HR do not change. A biphasic response was observed both for IL1-ß and TGF-ß expression and also for the presence of CD45 positive cells, with an acute increase (between 30 and 60 minutes) and a second increase, between 24 and 48 hours. Positive staining for iNOS increased in the earlier period (30 minutes) in perivascular adipose tissue and in a longer period (48 hours) in tunica adventitia. Immunoblotting to α-actin showed no alterations, suggesting that the applied dose of angiotensin II does not alter the aortic VSMCs phenotype. The results suggest that angiotensin II, even at doses that do not alter BP, induces the expression of inflammatory markers and migration of inflammatory cells into the aorta of normotensive mice. Thus, angiotensin II may increase the propensity to develop a cardiovascular injury, even in normotensive individuals.

Increase in Vascular Injury of Sodium Overloaded Mice May be Related to Vascular Angiotensin Modulation.

This study aimed to analyzing the effect of chronic sodium overload upon carotid and femoral injury, and its relation to vascular angiotensin modulation. Male C57Bl6 mice were divided in: control (cont), receiving 1% NaCl solution for 2 weeks (salt-2) or 12 weeks (salt-12). Two-weeks before the end of the study, a 2mm catheter was implanted around the left femoral and carotid arteries to induce injury. Blood pressure (BP) and heart rate (HR) were measured at the end of the study by tail plethysmography. Arteries were collected and prepared for histological analysis to determine arterial thickening and perivascular collagen deposition. Angiotensin II and Ang(1-7) were quantified in fresh arteries using the HPLC method. There were no differences in body weight, BP and HR. Intima/media ratio had a similar increase in both injured arteries of cont and salt-2 mice, but a more pronounced increase was observed in salt-12 mice (31.1±6%). On the other hand, sodium overload modified perivascular collagen deposition, increasing thick fibers (cont: 0.5%; salt-2: 3.4%; salt-12: 0.6%) and decreasing thin fibers (cont: 7.4%; salt-2: 0.5%; salt-12: 6.8%) in non-injured arteries. Injured arteries presented similar collagen fiber distribution. Angiotensin quantification showed increased Ang(1-7) in salt treated mice (salt-2: +72%; salt-12: +45%) with a concomitant decrease in Ang II (salt-2: -54%; salt-12: -60%). Vascular injury increased significantly Ang(1-7) in salt-12 mice (+80%), maintaining Ang II reduction similar to that of a non-injured artery. The lack of changes in BP and HR suggests that the structural changes observed may be due to non-hemodynamic mechanisms such as local renin-angiotensin system. Collagen evaluation suggests that sodium overload induces time-related changes in vascular remodeling. The increase of artery injury with concomitant increase in Ang(1-7) in 12-week treated mice shows a direct association between the duration of salt treatment and the magnitude of vascular injury.