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  • Most of the modifications in the

    2024-04-24

    Most of the modifications in the sympathetic nervous system occurring with aging, including decreased βAR responsiveness, increased circulating catecholamines, and overall hyposensitivity to adrenergic stress, are also observed in patients with failing hearts. Moreover, young people are more reactive to isoproterenol-induced increase in blood flow than elderly subjects [31]. Vascular tone is finely regulated by the intimal (endothelial cells, EC) and the medial (vascular smooth muscle cells, VSMC) layers [43], [44], [45] and both EC and VSMC express β2AR [46], [47], [48]. The age-related decline in β2AR function and successive cAMP generation is observed in diverse cardiovascular disorders, including atherosclerosis, hypertension, vascular insufficiency, and orthostatic hypotension, all conditions with significant mortality and morbidity [49], [50], [51], [52], [53]. The increased incidence of restenosis and atherosclerosis in aged people may also rely on the age-associated deterioration in βAR-mediated cAMP production, since cAMP may inhibit VSMC proliferation [45], [54]. A reduced responsiveness with age has been also reported for αAR in healthy subjects [55], with potential implications for reduced muscle blood flow and augmented blood pressure during exercise [56], [57], [58]. During the late 90’s the idea that the EC possessed functional βARs became more and more evident, and soon this system was seen as a therapeutic target [59], [60]. Nevertheless, the proangiogenic effects of the β2AR was firstly identified by our group in 2005 [47]. The picture was completed, when we finally demonstrated that the endothelium is the source of catecholamines that stimulate in a paracrine manner endothelial βARs [46]. These findings were further corroborated by the observation that also endothelial progenitor valdecoxib express β2AR and that the ability of this receptor to signaling to eNOS promotes angiogenesis through multiple mechanisms [61]. This ability is lost during aging. Strategies that aim to restore β2AR signaling in models where it is lost are effective to restore also impaired angiogenesis [47], [62]. For instance, in aging the enhancement of βAR signaling leads to the correction of impaired angiogenesis [10], [63], [64]. The overall incidence of cardiac disorders including heart failure, left ventricular hypertrophy, and arrhythmias, increases considerably with age [1], [65]. Elderly people appear to be particularly predisposed to the development of heart failure: such a diagnosis is the leading cause of hospitalizations in people >65 years of age [1], [15]. Additionally, alterations in ventricular relaxation and filling have been described with aging [64], [66]. The prevalence of atrial fibrillation reaches values of 17.8% in people >85 years [1], [67], [68]. The development of a non-regular pattern of electrical activity might have detrimental consequences in hearts that are relatively stiff and relax slowly [1], [69], [70]. Likewise, the prevalence of left ventricular hypertrophy increases with rising blood pressure and body mass index [71], [72] and studies in normotensive people indicate that myocardial wall thickness increases progressively with age [73]. In the vasculature an age-linked increase in intimal thickening has been reported, accompanied by luminal dilatation and reduction in distensibility, resulting in increased vessel stiffness. Indeed, pulse wave velocity, a noninvasive index of vascular stiffening, increases with age and has been associated with structural alterations in the media [13], [44], [48], [49], [64], [74], [75], [76].
    Adrenergic signaling in heart failure The SNS has prominent effects on cardiac physiology, including increases in atrioventricular conduction (positive dromotropy), heart rate (positive chronotropy), cardiac contractility (positive inotropy), and cardiac relaxation (positive lusitropy). Crucially, the SNS plays a crucial role in the regulation of vascular tone by controlling both peripheral resistance and cardiac output [77], [78].