Aging and the Brain Renin–Angiotensin System: Relevance to Age-Related Decline in Cardiac Function

Abstract

This article discusses evidence that impairments in control of autonomic outflow mediated by the brain renin-angiotensin system (RAS) contribute to the decline in baroreceptor reflex function and the development of insulin resistance that accompany hypertension and excess salt intake, especially during aging. Imbalances in the regulation of the sympathetic and parasympathetic limbs of the autonomic nervous system observed in older subjects underlie changes in heart-rate variability and play a role in the regulation of overall cardiac function. Age-related alterations in autonomic nervous system function may also explain the age-associated alterations in metabolism. Reduced heart-rate variability is linked to increased mortality in patients with cardiovascular disorders and, coupled with information that is known about local changes in the cardiac and brain RAS during aging, the evidence reveals potential mechanisms for the protective effects of systemic blockade of the RAS against agerelated changes that impact the heart. Executive summary-• Disturbances in the brain renin-angiotensin system as a result of aging or conditions of excess salt contribute to imbalances in autonomic nervous system function leading to impairments in baroreceptor reflex control of heart rate and energy metabolism.• Cardiac structural and functional abnormalities, both systolic and diastolic, may result as a component of their etiology, the age-related hypertension and accompanying baroreflex, insulin resistance or bodyweight changes that are secondary to the impaired autonomic function resulting from alterations in the brain renin-angiotensin system.• Reductions in Ang-(1-7) in tissues such as brain or heart during the aging process or other conditions such as excess salt intake, rather than frank increases in Ang II, appear to contribute to pathophysiologic changes in cardiac structure and function. [1,2]. Importantly, dietary salt excess has been shown to be an invariable determinant of the age-related changes in blood pressure and endorgan damage in many clinical and experimental studies. A large body of epidemiological and experimental evidence demonstrates a significant association between high salt intake and blood pressure as well as a rise in systolic and diastolic blood pressure with aging [3][4][5]. While these changes are presumed to be a major reason for the altered diastolic compliance of the senescent heart, age-related increases in arterial stiffness can further lead to vascularventricular uncoupling [6,7], which, when taken together, predispose to diastolic heart failure (DHF). Stimuli for this cardiovascular remodeling associated with aging and diastolic heart disease include hypertension, increases in bodyweight gain, insulin resistance and renal dysfunction [8]. A common feature associated with the conditions of excess salt or advanced age is impairment of the baroreceptor reflexes for control of heart rate. Reduced heart-rate variability accompanies the imbalance in the sympathetic and parasympathetic nervo...

The Tissue Renin-Angiotensin System and Its Role in the Pathogenesis of Major Human Diseases: Quo Vadis?

“…The circulating RAS components, such as AngII and Renin, decrease with age [ 30 , 31 , 32 , 33 ]. In contrast, the expression and levels of the pathological tRAS pathway increase with age, as shown in the heart, vasculature, and the brain [ 30 , 31 , 34 , 35 , 36 ]. Angiotensin II, the main effector of tRAS, was shown to promote vascular senescence onset and progression, leading to age-related vascular diseases [ 37 ].…”

Sympathetic nervous system as a target for aging and obesity-related cardiovascular diseases

“…Brain RAS has also been implicated in the pathogenesis of age-related increase in arterial pressure. In aging, an autonomic imbalance characterized by reduced parasympathetic activity is created as a result of an agerelated decline in Ang (1-7) generated by angiotensinconverting enzyme 2 (ACE2) by metabolizing Ang-II (Diz et al 2008). In contrast, there is overactivity of the SNS influenced by circulating or brain Ang-II along with leptin.…”

Angiotensin peptides and central autonomic regulation

“…In hypertensive (mRen2)27 rats, overexpression of mouse renin leads to high brain Ang I/Ang II/Ang-(1–7) in hypothalamic tissue, with high Ang II/low Ang-(1–7) in medullary tissue [11]. MAP is highest in young animals and declines with age along with decreases in cardiac function [3;12;13]. The BRS is impaired in young (mRen2)27 rats [14;15], and neither AT 1 nor Ang-(1–7) receptor blockade in the nTS alters BRS or MAP (Figure 1).…”