Vascular angiotensin II actions mediated by angiotensin II type 2 receptors

Altered reactivity of resistance vasculature contributes to hypertension in elastin insufficiency

Elastin (Eln) insufficiency in mice and humans is associated with hypertension and altered structure and mechanical properties of large arteries. However, it is not known to what extent functional or structural changes in resistance arteries contribute to the elevated blood pressure that is characteristic of Eln insufficiency. Here, we investigated how Eln insufficiency affects the structure and function of the resistance vasculature. A functional profile of resistance vasculature in Eln(+/-) mice was generated by assessing small mesenteric artery (MA) contractile and vasodilatory responses to vasoactive agents. We found that Eln haploinsufficiency had a modest effect on phenylephrine-induced vasoconstriction, whereas ANG II-evoked vasoconstriction was markedly increased. Blockade of ANG II type 2 receptors with PD-123319 or modulation of Rho kinase activity with the inhibitor Y-27632 attenuated the augmented vasoconstriction, whereas acute Y-27632 administration normalized blood pressure in Eln(+/-) mice. Sodium nitroprusside- and isoproterenol-induced vasodilatation were normal, whereas ACh-induced vasodilatation was severely impaired in Eln(+/-) MAs. Histologically, the number of smooth muscle layers did not change in Eln(+/-) MAs; however, an additional discontinuous layer of Eln appeared between the smooth muscle layers that was absent in wild-type arteries. We conclude that high blood pressure arising from Eln insufficiency is due partly to permanent changes in vascular tone as a result of increased sensitivity of the resistance vasculature to circulating ANG II and to impaired vasodilatory mechanisms arising from endothelial dysfunction characterized by impaired endothelium-dependent vasodilatation. Eln insufficiency causes augmented ANG II-induced vasoconstriction in part through a novel mechanism that facilitates contraction evoked by ANG II type 2 receptors and altered G protein signaling.

Angiotensin II receptor type 1 blockade decreases CTGF/CCN2-mediated damage and fibrosis in normal and dystrophic skeletal muscles

Connective tissue growth factor (CTGF/CCN-2) is mainly involved in the induction of extracellular matrix (ECM) proteins. The levels of CTGF correlate with the degree and severity of fibrosis in many tissues, including dystrophic skeletal muscle. The CTGF overexpression in tibialis anterior skeletal muscle using an adenoviral vector reproduced many of the features observed in dystrophic muscles including muscle damage and regeneration, fibrotic response and decrease in the skeletal muscle strength. The renin-angiotensin system is involved in the genesis and progression of fibrotic diseases through its main fibrotic components angiotensin-II and its transducer receptor AT-1. The use of AT-1 receptor blockers (ARB) has been shown to decrease fibrosis. In this paper, we show the effect of AT-1 receptor blockade on CTGF-dependent biological activity in skeletal muscle cells as well as the response to CTGF overexpression in normal skeletal muscle. Our results show that in myoblasts ARB decreased CTGF-mediated increase of ECM protein levels, extracellular signal regulated kinases 1/2 (ERK-1/2) phosphorylation and stress fibres formation. In tibialis anterior muscle overexpressing CTGF using an adenovirus, ARB treatment decreased CTGF-mediated increase of ECM molecules, α-SMA and ERK-1/2 phosphorylation levels. Quite remarkable, ARB was able to prevent the loss of contractile force of tibialis anterior muscles overexpressing CTGF. Finally, we show that ARB decreased the levels of fibrotic proteins, CTGF and ERK-1/2 phosphorylation augmented in a dystrophic skeletal muscle from mdx mice. We propose that ARB is a novel pharmacological tool that can be used to decrease the fibrosis induced by CTGF in skeletal muscle associated with muscular dystrophies.

Effects of aging, TNF-α, and exercise training on angiotensin II-induced vasoconstriction of rat skeletal muscle arterioles

Skeletal muscle vascular resistance during physical exertion is higher with old age. The purpose of this study was to determine whether 1) aging enhances angiotensin II (ANG II)-induced vasoconstriction; 2) the proinflammatory cytokine tumor necrosis factor (TNF)-α contributes to alterations in ANG II-mediated vasoconstriction with aging; 3) exercise training attenuates putative age-associated increases in ANG II-mediated vasoconstriction; and 4) the mechanism(s) through which aging and exercise training alters ANG II-induced vasoconstriction in skeletal muscle arterioles. Male Fischer 344 rats were assigned to four groups: young sedentary (4 mo), old sedentary (24 mo), young trained, and old trained. In a separate group of young sedentary and old sedentary animals, a TNF type 1 receptor inhibitor was administered subcutaneously for 10 wk. First-order arterioles were isolated from soleus and gastrocnemius muscles for in vitro experimentation. Old age augmented ANG II-induced vasoconstriction in both soleus (young: 27 ± 3%; old: 38 ± 4%) and gastrocnemius (young: 42 ± 6%; old: 64 ± 9%) muscle arterioles; this augmented vasoconstriction was abolished with the removal of the endothelium, N(G)-nitro-l-arginine methyl ester, and chronic inhibition of TNF-α. In addition, exercise training ameliorated the age-induced increase in ANG II vasoconstriction. These findings demonstrate that old age enhances and exercise training diminishes ANG II-induced vasoconstrictor responses in skeletal muscle arterioles through an endothelium-dependent nitric oxide synthase signaling pathway. In addition, the enhancement of ANG II vasoconstriction with old age appears to be related to a proinflammatory state.

Pathogenesis and clinical physiology of hypertension

Significant advances have been made in understanding the pathogenesis and clinical physiology of primary hypertension. This article presents an overview of the physiology of normal blood pressure control and the pathophysiologic mechanisms that predispose individuals and populations to primary hypertension. The role of genetics, environment, and the gene-environment interaction is discussed. The spectrum of changes in physiologic states that result in chronic increases of arterial blood pressure are reviewed. The nature and characteristics of feedback loops and the primary modulating systems, the central and peripheral nervous systems, and circulating and tissue hormones are reviewed. The role of the endothelium of the artery and its production of endothelin, nitric oxide, angiotensin II, as well as other vasoactive substances in response to various stimuli, is also discussed. A unifying pathway for the development of hypertension and the practical implications for the prevention and control of hypertension are discussed.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Regulation of central angiotensin type 1 receptors and sympathetic outflow in heart failure

Angiotensin type 1 receptors (AT(1)Rs) play a critical role in a variety of physiological functions and pathophysiological states. They have been strongly implicated in the modulation of sympathetic outflow in the brain. An understanding of the mechanisms by which AT(1)Rs are regulated in a variety of disease states that are characterized by sympathoexcitation is pivotal in development of new strategies for the treatment of these disorders. This review concentrates on several aspects of AT(1)R regulation in the setting of chronic heart failure (CHF). There is now good evidence that AT(1)R expression in neurons is mediated by activation of the transcription factor activator protein 1 (AP-1). This transcription factor and its component proteins are upregulated in the rostral ventrolateral medulla of animals with CHF. Because the increase in AT(1)R expression and transcription factor activation can be blocked by the AT(1)R antagonist losartan, a positive feedback mechanism of AT(1)R expression in CHF is suggested. Oxidative stress has also been implicated in the regulation of receptor expression. Recent data suggest that the newly discovered catabolic enzyme angiotensin-converting enzyme 2 (ACE2) may play a role in the modulation of AT(1)R expression by altering the balance between the octapeptide ANG II and ANG- (1-7). Finally, exercise training reduces both central oxidative stress and AT(1)R expression in animals with CHF. These data strongly suggest that multiple central and peripheral influences dynamically alter AT(1)R expression in CHF.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT1R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT2R) is thought to counter-regulate AT1R function. In this review, we describe the enhanced expression and function of AT2R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT2R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT1R-mediated overactivity and cardiovascular pathologies.