Effect of removal of adventitia on vascular smooth muscle contraction and relaxation

Fetal Undernutrition Modifies Vascular RAS Balance Enhancing Oxidative Damage and Contributing to Remodeling

Fetal stress is known to increase susceptibility to cardiometabolic diseases and hypertension in adult age in a process known as fetal programming. This study investigated the relationship between vascular RAS, oxidative damage and remodeling in fetal programming. Six-month old Sprague-Dawley offspring from mothers that were fed ad libitum (CONTROL) or with 50% intake during the second half of gestation (maternal undernutrition, MUN) were used. qPCR or immunohistochemistry were used to obtain the expression of receptors and enzymes. Plasma levels of carbonyls were measured by spectrophotometry. In mesenteric arteries from MUN rats we detected an upregulation of ACE, ACE2, AT₁ receptors and NADPH oxidase, and lower expression of AT₂, Mas and MrgD receptors compared to CONTROL. Systolic and diastolic blood pressure and plasma levels of carbonyls were higher in MUN than in CONTROL. Vascular morphology evidenced an increased media/lumen ratio and adventitia/lumen ratio, and more connective tissue in MUN compared to CONTROL. In conclusion, fetal undernutrition indices RAS alterations and oxidative damage which may contribute to the remodeling of mesenteric arteries, and increase the risk of adverse cardiovascular events and hypertension.

The Local Regulation of Vascular Function: From an Inside-Outside to an Outside-Inside Model

Our understanding of the regulation of vascular function, specifically that of vasomotion, has evolved dramatically over the past few decades. The classic conception of a vascular system solely regulated by circulating hormones and sympathetic innervation gave way to a vision of a local regulation. Initially by the so-called, autacoids like prostacyclin, which represented the first endothelium-derived paracrine regulator of smooth muscle. This was the prelude of the EDRF-nitric oxide age that has occupied vascular scientists for nearly 30 years. Endothelial cells revealed to have the ability to generate numerous mediators besides prostacyclin and nitric oxide (NO). The need to classify these substances led to the coining of the terms: endothelium-derived relaxing, hyperpolarizing and contracting factors, which included various prostaglandins, thromboxane A2, endothelin, as well numerous candidates for the hyperpolarizing factor. The opposite layer of the vascular wall, the adventitia, eventually and for a quite short period of time, enjoyed the attention of some vascular physiologists. Adventitial fibroblasts were recognized as paracrine cells to the smooth muscle because of their ability to produce some substances such as superoxide. Remarkably, this took place before our awareness of the functional potential of another adventitial cell, the adipocyte. Possibly, because the perivascular adipose tissue (PVAT) was systematically removed during the experiments as considered a non-vascular artifact tissue, it took quite long to be considered a major source of paracrine substances. These are now being integrated in the vast pool of mediators synthesized by adipocytes, known as adipokines. They include hormones involved in metabolic regulation, like leptin or adiponectin; classic vascular mediators like NO, angiotensin II or catecholamines; and inflammatory mediators or adipocytokines. The first substance studied was an anti-contractile factor named adipose-derived relaxing factor of uncertain chemical nature but possibly, some of the relaxing mediators mentioned above are behind this factor. This manuscript intends to review the vascular regulation from the point of view of the paracrine control exerted by the cells present in the vascular environment, namely, endothelial, adventitial, adipocyte and vascular stromal cells.

Postnatal overnutrition affects metabolic and vascular function reflected by physiological and histological changes in the aorta of adult Wistar rats

Rigorous nutritional care during early life leads to healthy adulthood. Cardiovascular and metabolic disorders, the most prevalent clinical challenges worldwide, are epidemiologically linked to poor nutritional habits throughout life. We aimed to understand whether postnatal overnutrition (PO) initiated during lactation affects metabolic markers and vascular function later in life. To test this hypothetical effect, we studied a PO Wistar rat model based on adjusting litter size at the third day of age to three pups and eight for the control group (C). Systemic parameters such as body weight and food intake were significantly increased in adult rats, measured up to 36 weeks. Moreover, fat mass, triglycerides, insulin and systolic blood pressure were all significantly increased in the PO group. Furthermore, we assessed whether these alterations would affect morphological and functional parameters in isolated vessels. Consistent with systemic alterations of the vasculature, contraction of thoracic aortic rings, determined by dose-response curves to norepinephrine (NE), was significantly reduced in PO rats. Histological stains revealed that the relative area of collagen was higher and the elastic fiber density was lower in the distal rings of PO rats. Altogether, our results highlight the critical importance of having a healthy neonatal nutrition to prevent harmful metabolic and vascular alterations during adulthood.

The transition of smooth muscle cells from a contractile to a migratory, phagocytic phenotype: direct demonstration of phenotypic modulation

Key points

Smooth muscle cell (SMC) phenotypic conversion from a contractile to a migratory phenotype is proposed to underlie cardiovascular disease but its contribution to vascular remodelling and even its existence have recently been questioned.

Tracking the fate of individual SMCs is difficult as no specific markers of migratory SMCs exist.

This study used a novel, prolonged time‐lapse imaging approach to continuously track the behaviour of unambiguously identified, fully differentiated SMCs.

In response to serum, highly‐elongated, contractile SMCs initially rounded up, before spreading and migrating and these migratory cells displayed clear phagocytic activity.

This study provides a direct demonstration of the transition of fully contractile SMCs to a non‐contractile, migratory phenotype with phagocytic capacity that may act as a macrophage‐like cell.

Abstract

Atherosclerotic plaques are populated with smooth muscle cells (SMCs) and macrophages. SMCs are thought to accumulate in plaques because fully differentiated, contractile SMCs reprogramme into a ‘synthetic’ migratory phenotype, so‐called phenotypic modulation, whilst plaque macrophages are thought to derive from blood‐borne myeloid cells. Recently, these views have been challenged, with reports that SMC phenotypic modulation may not occur during vascular remodelling and that plaque macrophages may not be of haematopoietic origin. Following the fate of SMCs is complicated by the lack of specific markers for the migratory phenotype and direct demonstrations of phenotypic modulation are lacking. Therefore, we employed long‐term, high‐resolution, time‐lapse microscopy to track the fate of unambiguously identified, fully‐differentiated, contractile SMCs in response to the growth factors present in serum. Phenotypic modulation was clearly observed. The highly elongated, contractile SMCs initially rounded up, for 1–3 days, before spreading outwards. Once spread, the SMCs became motile and displayed dynamic cell‐cell communication behaviours. Significantly, they also displayed clear evidence of phagocytic activity. This macrophage‐like behaviour was confirmed by their internalisation of 1 μm fluorescent latex beads. However, migratory SMCs did not uptake acetylated low‐density lipoprotein or express the classic macrophage marker CD68. These results directly demonstrate that SMCs may rapidly undergo phenotypic modulation and develop phagocytic capabilities. Resident SMCs may provide a potential source of macrophages in vascular remodelling.

Smooth muscle cell (SMC) phenotypic conversion from a contractile to a migratory phenotype is proposed to underlie cardiovascular disease but its contribution to vascular remodelling and even its existence have recently been questioned.

Tracking the fate of individual SMCs is difficult as no specific markers of migratory SMCs exist.

This study used a novel, prolonged time‐lapse imaging approach to continuously track the behaviour of unambiguously identified, fully differentiated SMCs.

In response to serum, highly‐elongated, contractile SMCs initially rounded up, before spreading and migrating and these migratory cells displayed clear phagocytic activity.

This study provides a direct demonstration of the transition of fully contractile SMCs to a non‐contractile, migratory phenotype with phagocytic capacity that may act as a macrophage‐like cell.

The paracrine control of vascular motion. A historical perspective

During the last quarter of the past century, the leading role the endocrine and nervous systems had on the regulation of vasomotion, shifted towards a more paracrine-based regulation. This begun with the recognition of endothelial cells as active players of vascular control, when the vessel's intimal layer was identified as the main source of prostacyclin and was followed by the discovery of an endothelium-derived smooth muscle cell relaxing factor (EDRF). The new position acquired by endothelial cells prompted the discovery of other endothelium-derived regulatory products: vasoconstrictors, generally known as EDCFs, endothelin, and other vasodilators with hyperpolarizing properties (EDHFs). While this research was taking place, a quest for the discovery of the nature of EDRF carried back to a research line commenced a decade earlier: the recently found intracellular messenger cGMP and nitrovasodilators. Both were smooth muscle relaxants and appeared to interact in a hormonal fashion. Prejudice against an unconventional gaseous molecule delayed the acceptance that EDRF was nitric oxide (NO). When this happened, a new era of research that exceeded the vascular field commenced. The discovery of the pathway for NO synthesis from L-arginine involved the clever assembling of numerous unrelated observations of different areas of knowledge. The last ten years of research on the paracrine regulation of the vascular wall has shifted to perivascular fat (PVAT), which is beginning to be regarded as the fourth layer of the vascular wall. Starting with the discovery of an adipose-derived relaxing substance (ADRF), the role that different adipokines have on the paracrine control of vasomotion is now filling the research activity of many vascular pharmacology labs, and surprising interactions between the endothelium, PVAT and smooth muscle are being unveiled.

What is the source of anticontractile factor released by the pedicle of human internal thoracic artery?

OBJECTIVES

Perivascular tissue (PVT) surrounding human internal thoracic artery (ITA) releases an unidentified anticontractile factor. The exact source of perivascular tissue-derived relaxing factor (PVRF) is unknown, although the adventitia and adipose tissue have both been suggested as primary candidates, hence the name adventitia or adipocyte-derived relaxing factor (ADRF). To look for the source of ADRF, we examined the dilatory response of human ITA to PVT aliquots in their histological composition.

METHODS

We studied isolated ITA segments from 20 patients subjected to coronary artery surgery. The vessels were skeletonized in vitro. ITA rings and PVT were incubated in separate isolated organ baths. The arterial rings were suspended on stainless steel wire hooks in the organ bath chamber. Vessel wall tension was measured with an isometric force transducer. Skeletonized ITA segments were precontracted with 10(-5.5) M phenylephrine. The 5 ml PVT aliquots were next transferred to the ITA tissue bath, resulting in its relaxation. Subsequently, the whole PVT used during experiment was fixed in paraformaldehyde and subjected to histological examination. Tissue was paraffin-embedded, sectioned and stained with haematoxylin and eosin. The paraffin blocks containing PVT were cut into slices every 800 μm to create three-dimensional model. Every PVT specimen was evaluated morphometrically using the Image Pro Plus software to assess the content of three basic kinds of tissues. The ITA relaxation to PVT aliquots was correlated to the histological composition of the PVT.

RESULTS

Phenylephrine elicited a 37.82 mN (Q1 = 26.49; Q3 = 46.31) contraction of the ITA. The addition of PVT aliquots to the skeletonized ITA induced a 54.17% (Q1 = 16.73; Q3 = 68.21) relaxation. The median PVT weight was 786 mg (Q1 = 562; Q3 = 976). The PVT composition was as follows: 30.5% (Q1 = 18.5; Q3 = 55.2) adipose tissue, 53.5 (Q1 = 24.6; Q3 = 66.5) muscular tissue and 13.5% (Q1 = 9.9; Q3 = 20.0) connective tissue. This translated into 197.7 mg of adipose tissue (Q1 = 142.2; Q3 = 393.2), 378.9 mg (Q1 = 178.8; Q3 = 537.0) of muscular tissue and 92.4 mg (Q1 = 68.6; Q3 = 185.8) of connective tissue. Neither PVT mass (r = 0.2, P = 0.92) nor adipose tissue (r = -0.2, P = 0.34), muscular tissue (r = 0.3, P = 0.18) or connective tissue (r = -0.2, P = 0.41) content correlated with ITA relaxation response to PVT aliquots.

CONCLUSIONS

Adipose tissue from the pedicled ITA graft is an unlikely source of ADRF.

Salusin-β contributes to vascular remodeling associated with hypertension via promoting vascular smooth muscle cell proliferation and vascular fibrosis

Vascular smooth muscle cell (VSMC) proliferation and vascular fibrosis are closely linked with hypertension and atherosclerosis. Salusin-β is a bioactive peptide involved in the pathogenesis of atherosclerosis. However, it is still largely undefined whether salusin-β is a potential candidate in the VSMC proliferation and vascular fibrosis. Experiments were carried out in human vascular smooth muscle cells (VSMCs) and in rats with intravenous injection of lentivirus expressing salusin-β. In vitro, salusin-β promoted VSMCs proliferation, which was attenuated by adenylate cyclase inhibitor SQ22536, PKA inhibitor Rp-cAMP, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478, ERK inhibitor U0126 or cAMP response element binding protein (CREB) inhibitor KG501. It promoted the phosphorylation of ERK1/2, CREB and EGFR, which were abolished by SQ22536 or Rp-cAMP. Furthermore, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478 diminished the salusin-β-evoked ERK1/2 and CREB phosphorylation. On the other hand, salusin-β increased collagen-I, collagen-III, fibronectin and connective tissue growth factor (CTGF) mRNA and phosphorylation of Smad2/3, which were prevented by ALK5 inhibitor A83-01. In vivo, salusin-β overexpression increased the media thickness, media/lumen ratio coupled with ERK1/2, CREB, EGFR and Smad2/3 phosphorylation, as well as the mRNA of collagen-I, collagen-III, fibronectin, transforming growth factor-β1 (TGF-β1) and CTGF in arteries. Moreover, salusin-β overexpression in rats caused severe hypertension. Intravenous injection of salusin-β dose-relatedly increased blood pressure, but excessive salusin-β decreased blood pressure and heart rate. These results indicate that salusin-β promotes VSMC proliferation via cAMP-PKA-EGFR-CREB/ERK pathway and vascular fibrosis via TGF-β1-Smad pathway. Increased salusin-β contributes to vascular remodeling and hypertension.

The Relationship between Vascular Function and the Autonomic Nervous System

Endothelial dysfunction and autonomic nervous system dysfunction are both risk factors for atherosclerosis. There is evidence demonstrating that there is a close interrelationship between these two systems. In hypertension, endothelial dysfunction affects the pathologic process through autonomic nervous pathways, and the pathophysiological process of autonomic neuropathy in diabetes mellitus is closely related with vascular function. However, detailed mechanisms of this interrelationship have not been clearly explained. In this review, we summarize findings concerning the interrelationship between vascular function and the autonomic nervous system from both experimental and clinical studies. The clarification of this interrelationship may provide more comprehensive risk stratification and a new effective therapeutic strategy against atherosclerosis.

The adventitia: Essential role in pulmonary vascular remodeling

A rapidly emerging concept is that the vascular adventitia acts as a biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. It is the most complex compartment of the vessel wall and comprises a variety of cells including fibroblasts, immunomodulatory cells, resident progenitor cells, vasa vasorum endothelial cells, and adrenergic nerves. In response to vascular stress or injury, resident adventitial cells are often the first to be activated and reprogrammed to then influence tone and structure of the vessel wall. Experimental data indicate that the adventitial fibroblast, the most abundant cellular constituent of adventitia, is a critical regulator of vascular wall function. In response to vascular stresses such as overdistension, hypoxia, or infection, the adventitial fibroblast is activated and undergoes phenotypic changes that include proliferation, differentiation, and production of extracellular matrix proteins and adhesion molecules, release of reactive oxygen species, chemokines, cytokines, growth factors, and metalloproteinases that, collectively, affect medial smooth muscle cell tone and growth directly and that stimulate recruitment and retention of circulating inflammatory and progenitor cells to the vessel wall. Resident dendritic cells also participate in "sensing" vascular stress and actively communicate with fibroblasts and progenitor cells to simulate repair processes that involve expansion of the vasa vasorum, which acts as a conduit for further delivery of inflammatory/progenitor cells. This review presents the current evidence demonstrating that the adventitia acts as a key regulator of pulmonary vascular wall function and structure from the "outside in."

Adventitial dissection: a simple and effective way to reduce radial artery spasm in coronary bypass surgery

OBJECTIVES

Over the last two decades, the radial artery (RA) has become a routinely used conduit for coronary artery bypass graft surgery. One potential disadvantage of the radial artery is its higher susceptibility to vasospasm compared with other arterial grafts. We investigated whether adventitial dissection of the radial artery can reduce vasoconstriction and increase free blood flow.

METHODS

Following harvesting, the adventitia of the radial artery was dissected using coronary scissors. Surplus distal radial artery segments (n = 35) with and without adventitial dissection of patients undergoing coronary artery bypass surgery were collected and pairwise assessment of vasoreactivity to potassium chloride, U46619 and acetylcholine was performed in organ bath experiments. Free blood flow was measured before and after adventitial dissection.

RESULTS

Full curve and maximal vasoconstriction of the RA to potassium chloride (P = 0.015 and 0.001) and U46619 (P = 0.048 and 0.001) was significantly reduced after adventitial dissection compared with non-adventitial dissected radial arteries. Endothelium-dependent relaxation to acetylcholine of adventitial dissected radial arteries was significantly increased (P = 0.006) compared with non-adventitial dissected radial arteries. Maximal vasorelaxation to acetylcholine was significantly increased for adventitial dissected radial arteries compared with non-adventitial dissected radial arteries (P = 0.018). Free blood flow was significantly increased after adventitial dissection (P = 0.037).

CONCLUSIONS

The adventitial dissected radial artery is less susceptible to vasoconstriction and more prone to vasorelaxation ex vivo and shows an increased free blood flow. Therefore, we suggest adventitial dissection of the radial artery graft to reduce vasospasm for arterial revascularization in coronary artery bypass surgery.

Mechanical stretch changes coronary artery fibroblasts function by upregulating HSF1 protein expression

The study is designed to investigate effect of mechanical stretch on the function of fibroblast cells. Human coronary artery fibroblasts were cultured. They were divided into two groups: stretch group (stretch for 24h) and no-stretch group (did not stretch). ELISA analysis was used for detection of collagen secretion. CCK-8 method was used for detection of cells proliferation. RT-PCR method was used for detection of MMP, TIMP, IL-6, alpha-SMA, HSF1 and HSP70 mRNA expression. Western-blotting method was used for detection of HSF1 protein expression. Results showed that cells proliferation in stretch group was stronger than that in no-stretch group. Hydroxyproline secretion in stretch group was more than that in no-stretch group. MMP-9/TIMP, alpha-SMA, IL-6, HSF1 and HSP70 in stretch group was higher than those in no-stretch group. Western-blotting analysis showed that HSF1 protein expression was upregulated in stretch group. It can be concluded that mechanical stretch changed human coronary artery fibroblasts cells proliferation, collagen formation, the secretion of inflammatory factor possibly by upregulating HSF1 protein expression.

Hypertension in metabolic syndrome: vascular pathophysiology

METABOLIC SYNDROME IS A CLUSTER OF METABOLIC AND CARDIOVASCULAR SYMPTOMS: insulin resistance (IR), obesity, dyslipemia. Hypertension and vascular disorders are central to this syndrome. After a brief historical review, we discuss the role of sympathetic tone. Subsequently, we examine the link between endothelial dysfunction and IR. NO is involved in the insulin-elicited capillary vasodilatation. The insulin-signaling pathways causing NO release are different to the classical. There is a vasodilatory pathway with activation of NO synthase through Akt, and a vasoconstrictor pathway that involves the release of endothelin-1 via MAPK. IR is associated with an imbalance between both pathways in favour of the vasoconstrictor one. We also consider the link between hypertension and IR: the insulin hypothesis of hypertension. Next we discuss the importance of perivascular adipose tissue and the role of adipokines that possess vasoactive properties. Finally, animal models used in the study of vascular function of metabolic syndrome are reviewed. In particular, the Zucker fatty rat and the spontaneously hypertensive obese rat (SHROB). This one suffers macro- and microvascular malfunction due to a failure in the NO system and an abnormally high release of vasoconstrictor prostaglandins, all this alleviated with glitazones used for metabolic syndrome therapy.

Two-layer model of coronary artery vasoactivity

Since vascular tone is regulated by smooth muscle cells in the media layer, a multilayer mechanical model is required for blood vessels. Here, we performed biaxial mechanical tests in the intima-media layer of right coronary artery to determine the passive and active properties in conjunction with the passive properties of adventitia for a full vessel wall model. A two-layer (intima-media and adventitia) model was developed to determine the transmural stress and stretch across the vessel wall. The mean ± SE values of the outer diameters of intima-media layers at transmural pressure of 60 mmHg in active state were 3.17 ± 0.16 and 3.07 ± 0.18 mm at axial stretch ratio of 1.2 and 1.3, respectively, which were significantly smaller than those in passive state (i.e., 3.62 ± 0.19 and 3.49 ± 0.22 mm, respectively, P < 0.05). The inner and outer diameters in no-load state of intima-media layers were 1.17 ± 0.09 and 2.08 ± 0.09 mm, respectively. The opening angles in zero-stress state had values of 159 ± 21° for intima-media layers and 98 ± 15° for adventitia layers, which suggests a residual strain between the two layers. There were slightly decreased active circumferential stresses (<10%), but significantly decreased active axial stresses (>25%) in the intima-media layer compared with those in the intact vessel. This suggests that the adventitia layer affects vascular contraction. The two-layer analysis showed that the intima-media layer bears the majority of circumferential tensions, in contrast to the adventitia layer, while contraction results in decreased stress and stretch in both layers.

Pseudostatic and dynamic nanomechanics of the tunica adventitia in elastic arteries using atomic force microscopy

Tunica adventitia, the outer layer of blood vessels, is an important structural feature, predominantly consisting of collagen fibrils. This study uses pseudostatic atomic force microscopy (AFM) nanoindentation at physiological conditions to show that the distribution of indentation modulus and viscous creep for the tunica adventitia of porcine aorta and pulmonary artery are distinct. Dynamic nanoindentation demonstrates that the viscous dissipation of the tunica adventitia of the aorta is greater than the pulmonary artery. We suggest that this mechanical property of the aortic adventitia is functionally advantageous due to the higher blood pressure within this vessel during the cardiac cycle. The effects on pulsatile deformation and dissipative energy losses are discussed.

The role of perivascular adipose tissue in vascular smooth muscle cell growth

Adipose tissue is the largest endocrine organ, producing various adipokines and many other substances. Almost all blood vessels are surrounded by perivascular adipose tissue (PVAT), which has not received research attention until recently. This review will discuss the paracrine actions of PVAT on the growth of underlying vascular smooth muscle cells (VSMCs). PVAT can release growth factors and inhibitors. Visfatin is the first identified growth factor derived from PVAT. Decreased adiponectin and increased tumour necrosis factor-α in PVAT play a pathological role for neointimal hyperplasia after endovascular injury. PVAT-derived angiotensin II, angiotensin 1-7, reactive oxygen species, complement component 3, NO and H(2) S have a paracrine action on VSMC contraction, endothelial or fibroblast function; however, their paracrine actions on VSMC growth remain to be directly verified. Factors such as monocyte chemoattractant protein-1, interleukin-6, interleukin-8, leptin, resistin, plasminogen activator inhibitor type-1, adrenomedullin, free fatty acids, glucocorticoids and sex hormones can be released from adipose tissue and can regulate VSMC growth. Most of them have been verified for their secretion by PVAT; however, their paracrine functions are unknown. Obesity, vascular injury, aging and infection may affect PVAT, causing adipocyte abnormality and inflammatory cell infiltration, inducing imbalance of PVAT-derived growth factors and inhibitors, leading to VSMC growth and finally resulting in development of proliferative vascular disease, including atherosclerosis, restenosis and hypertension. In the future, using cell-specific gene interventions and local treatments may provide definitive evidence for identification of key factor(s) involved in PVAT dysfunction-induced vascular disease and thus may help to develop new therapies.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Myofibroblast-mediated adventitial remodeling: an underestimated player in arterial pathology

The arterial adventitia has been long considered an essentially supportive tissue; however, more and more data suggest that it plays a major role in the modulation of the vascular tone by complex interactions with structures located within intima and media. The purpose of this review is to summarize these data and to describe the mechanisms involved in adventitia/media and adventitia/intima cross-talk. In response to a plethora of stimuli, the adventitia undergoes remodeling processes, resulting in positive (adaptive) remodeling, negative (constrictive) remodeling, or both. The differentiation of the adventitial fibroblast into myofibroblast (MF), a key player of wound healing and fibrosis development, is a hallmark of negative remodeling; this can lead to vessel stenosis and thus contribute to major cardiovascular diseases. The mechanisms of fibroblast-to-MF differentiation and the role of the MF in adventitial remodeling are highlighted herein.

Expression levels of TRPC1 and TRPC6 ion channels are reciprocally altered in aging rat aorta: implications for age-related vasospastic disorders

We previously showed that the expression of transient receptor potential canonical (TRPC)6 ion channel elevated when TRPC1 was knocked down in A7r5 cultured vascular smooth muscle cells. Therefore, the purpose of this study was to explore whether TRPC6 is also upregulated in aging rat aorta comparable to that of TRPC1 in longitudinal in vivo aging model. We further investigated a possible causal relationship between altered phenylephrine-induced contractions and the expression levels of TRPC6, a purported essential component of alpha-adrenergic receptor signaling in aging aorta. Immunoblot analysis showed that TRPC1 protein levels significantly decreased whereas TRPC6 increased drastically in aorta from 16- to 20-month-old rats compared to that from 2 to 4 months. Immunohistochemical data demonstrated spatial changes in TRPC6 expression within the smooth muscle layers along with increased detection in the adventitia of the aged rat aorta. The phenylephrine-induced contractions were potentiated in aging aorta. In conclusion, based on this aging model, TRPC6 overexpression could be related with TRPC1 downregulation and might be responsible for the increased adrenoceptor sensitivity which contributes to the development of age-related vasospastic disorders.

Effects of removing the adventitia on the mechanical properties of ovine femoral arteries in vivo and in vitro

BACKGROUND

The aims were to characterize in muscular arteries (a) the passive and active effects of the adventitia on vessel biomechanical properties and conduit function (CF), and (b) potential differences between the adventitial role in elastic and muscular arteries.

METHODS AND RESULTS

Ovine femoral arteries were studied in vivo and in vitro (reduced smooth muscle-tone) in a circulation mock-up during hemodynamic conditions similar to those found in vivo. Pressure and diameter were assessed before and after removing the adventitia. The arterial compliance, distensibility, stiffness beta-index and CF were quantified. Results were compared with those obtained in brachiocephalic trunks. In vivo, after removing the adventitia there was a nonsignificant diameter reduction and an increase in stiffness (P<0.05). The CF decreased in the early recordings (P<0.02). In vitro, there were no biomechanical changes but vascular dilatation after the adventitia removal. Biomechanical changes associated with the adventitia removal were higher in muscular arteries, whereas diameter changes were major in elastic vessels.

CONCLUSIONS

After removing the adventitia, (a) the arterial stiffness and CF were modified in vivo only, suggesting the changes could be ascribed to variations in smooth muscle tone, and (b) changes in elastic and muscular arteries were quantitatively different.

Adventitial fibroblasts in vascular structure and function: the role of oxidative stress and beyondThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

The vascular adventitia, defined as the area between the external elastic lamina and the outermost edge of the blood vessel, is composed primarily of fibroblasts and for years was thought to be merely a passive structural support for the blood vessel. Consequently, studies pertaining to the role of the adventitia in regulating vascular function have been far outnumbered by those regarding the vascular endothelium. However, recent work has begun to reveal the dynamic properties of the adventitia. It was therefore the aim of this review to provide an overview of the existing knowledge demonstrating the role of the adventitia in regulating vessel structure and function. The main topics covered in this review include the cellular composition of the adventitia and the role of the adventitia in vascular oxidative stress, vasomotor responses, extracellular matrix protein expression, growth factor expression, and endothelin-1 (ET-1) expression. Recent evidence suggests that the adventitia is a major producer of vascular reactive oxygen species. It displays a distinct response to injury, hypoxia, and pulmonary hypertension, mediating vascular remodelling, repair, and extracellular matrix deposition. It may also play a role in regulating vascular tone. More recently, it has been reported that adventitial fibroblasts can produce ET-1 after Ang II treatment. Additionally, emerging evidence suggests that the adventitia may be a potent source of vasoactive hormones such as growth factors and ET-1, which may regulate vascular structure and function via autocrine or paracrine signalling mechanisms. Despite these findings, many important questions regarding the role of the vascular adventitia remain unanswered, suggesting the need for further research to determine its exact function in health and disease.

Endothelial dysfunction in spontaneously hypertensive rats: focus on methodological aspects

Despite the apparent consensus on the existence of endothelial dysfunction in conduit and resistance arteries of spontaneously hypertensive rats (SHR), a commonly employed experimental model of hypertension, there are a number of reports showing that endothelium-dependent vasodilatory responses are similar, or even increased, in SHR compared with their normotensive counterparts. The present paper aims to discuss the rationale for these apparent discrepancies, including the effect of age, type of artery and methodological aspects. Data from the literature indicate that the age of the animal is a contributing factor and that endothelial dysfunction is likely to be a consequence of hypertension. In addition, the use of antioxidant additives, such as ascorbic acid or ethylene diaminetetraacetic acid, and differences in the level of initial arterial stretch, might also be of importance because they may modify the oxidative status of the artery and the levels of vasoactive factors released by the endothelium.

Evaluation of dynamic response and biomechanical properties of isolated blood vessels

In this study we present the experimental and mathematical model for a precise assessment of isolated blood vessels dynamic response under a sudden change of blood pressure. Only the end points within the time interval of the considered dynamic response of the blood vessel, or so-called "alternate steady states" of the processes, were usually considered in various studies. These studies do not provide an insight how the process variables change between these alternate steady states. Isolated blood vessels (rat abdominal aorta) were used to determine how the process dynamics can be described in detailed quantitative terms by mathematical parameters. The experimental model and mathematical procedures presented in this study describe precisely (at a high sensitivity level) the time history of the pressure and the diameter change in between alternate steady states, when an abrupt change of blood pressure occurs at the vessel outlet. Also, the experimental model and mathematical procedures were used to determine changes in the stress-strain law, caused by the action of L-arginine. The presented experimental design and mathematical model can be used for assessment of isolated blood vessel dynamic responses under different stimuli, such as drug effects, electrostimulation etc.

Hypertonic and isotonic potassium solutions have different effects on vessel contractility resulting in differences in optimal resting tension in rat aorta

AIM

To compare high K(+ )-induced contraction and optimal resting tension measured by two commonly used techniques of hypertonic and isotonic K(+ ) in aortas with and without adventitial fat from various age rats.

METHODS

Three age groups of rats (15, 25, and 62 weeks) were used to prepare thoracic aortic rings in which adventitial fat was either removed or left intact. High K(+ ) (30 mmol/L)-induced contractions were observed under increasing resting tensions of 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 g. Optimal resting tension was the resting tension at which the aorta showed a maximal contraction.

RESULTS

The contractions induced by 2 kinds of high K(+ ) were significantly different. Hypertonic and isotonic K(+ ) induced a different style of contraction, and the pattern varied with different ages. At the age of 15 weeks, isotonic K(+ )-induced contractions were greater than hypertonic K+-induced contractions. However, at the age of 62 weeks, isotonic K(+ )-induced contractions were smaller than hypertonic K(+ )-induced contractions. Optimal resting tensions measured by 2 kinds of high K(+ ) were inconsistent. Optimal resting tensions in different kinds of aortic preparations from various age rats were almost a constant of 2 g, determined by isotonic K(+ ), but a variable, determined by hypertonic K(+ ). The adventitial fat could delay the development of high K(+ )-induced contractions at different resting tensions, but had little effect on the maximal contractions.

CONCLUSION

Hypertonic and isotonic K(+ ) may produce different contractions resulting in differences in optimal resting tension in rat aorta.

Vascular Remodeling in Transplant Vasculopathy

As therapeutic strategies to prevent acute rejection progressively improve, transplant vasculopathy (TV) constitutes the single most important limitation for long-term functioning of solid organ allografts. In TV, allograft arteries characteristically develop severe, diffuse intimal hyperplastic lesions that eventually compromise luminal flow and cause ischemic graft failure. Traditional immunosuppressive strategies that check acute allograft rejection do not prevent TV; indeed 50% of transplant recipients will have significant disease within five years of organ transplantation, and 90% will have significant TV a decade after their surgery. TV can involve the entire length of the transplanted arterial bed, including penetrating intraorgan arterioles. Indeed, the luminal narrowing of such penetrating vessels may be the most functionally significant because arterioles represent the major contributors to tissue vascular resistance. Because of the diffuseness of TV involvement in the allograft vascular bed, the only currently definitive therapy requires re-transplantation. Nevertheless, as we better understand the pathogenesis and critical mediators of these lesions, pharmacological advances can be anticipated. Other articles in this thematic review series focus on the specifics of the inciting injury, the cytokines and chemokines that drive TV development, and the nature of the recruited cells in TV lesions, as well as the pathogenic similarities between TV and other vascular lesions such as atherosclerosis. This review focuses on the mechanisms of vascular wall remodeling in TV, including the intimal accumulation of smooth muscle-like cells and associated extracellular matrix, medial smooth muscle cell degeneration, and adventitial fibrosis. A brief overview highlights the aneurysmal changes that can accrue when vessel wall inflammation has a cytokine profile distinct from the typical proinflammatory interferon-gamma-dominated milieu.

Role of the adventitia in pulmonary vascular remodeling

An increasing volume of experimental data indicates that the adventitial fibroblast, in both the pulmonary and systemic circulations, is a critical regulator of vascular wall function in health and disease. A rapidly emerging concept is that the vascular adventitia acts as biological processing center for the retrieval, integration, storage, and release of key regulators of vessel wall function. In response to stress or injury, resident adventitial cells can be activated and reprogrammed to exhibit different functional and structural behaviors. In fact, under certain conditions, the adventitial compartment may be considered the principal injury-sensing tissue of the vessel wall. In response to vascular stresses such as overdistension and hypoxia, the adventitial fibroblast is activated and undergoes phenotypic changes, which include proliferation, differentiation, upregulation of contractile and extracellular matrix proteins, and release of factors that directly affect medial smooth muscle cell tone and growth and that stimulate recruitment of inflammatory and progenitor cells to the vessel wall. Each of these changes in fibroblast phenotype modulates either directly or indirectly changes in overall vascular function and structure. The purpose of this review is to present the current evidence demonstrating that the adventitial fibroblast acts as a key regulator of pulmonary vascular function and structure from the "outside-in."

Adventitia contribution in vascular tone: insights from adventitia‐derived cells in a tissue‐engineered human blood vessel

Whether the adventitia component of blood vessels directly participates in the regulation of vascular tone remains to be demonstrated. We have recently developed a human tissue-engineered blood vessel comprising the three tunicae of a native blood vessel using the self-assembly approach. To investigate the role of the adventitia in the modulation of vascular tone, this tissue-engineering method was used to produce three vascular constructs from cells explanted and proliferated from donor vessel tunicae 1) an adventitia + a media, or only 2) an adventitia, or 3) a media. The vasoconstriction responses of these 3 constructs to endothelin, the most potent vasopressor known up-to-date, as well as to nonselective and selective agonists and antagonists, were compared. The adventitia contracted to endothelin-1, -2, whereas the media and the media+adventitia contracted to all three endothelins. Endothelin-induced contraction of the adventitia was dependent on ET(A) receptors, whereas that of the media and the adventitia+media was ET(A) and ET(B) receptor-dependent. RT-PCR studies corroborated these results. SNP induced a dose-dependent relaxation of the three tissue constructs. We also demonstrated that the endothelin-converting enzyme, responsible for the formation of the active endothelin peptides, was present and functional in the adventitia. In conclusion, this is the first direct demonstration that the adventitia has the capacity to contract and relax in response to vasoactive factors. The present study suggests that the adventitia of a blood vessel could play a greater role than expected in the modulation of blood vessel tone.

Adventitial dysfunction: an evolutionary model for understanding atherosclerosis

Endothelial and smooth muscle dysfunctions are widely implicated in the pathogenesis of atherosclerosis. Modern mechanical and pharmacologic treatments aim to remodel abnormalities of the vessel intima and media. We hypothesize that adventitial dysfunction comprises the dominant source of atherosclerosis by originating many endothelial and smooth muscle abnormalities. The autonomic nervous system innervates the adventitia, and autonomic dysfunction induces many end-organ dysfunctions including inflammation and thrombosis. The link between diabetes and atherosclerosis may operate through adventitial autonomic neuropathy. Smoking may promote atherosclerosis by inducing adventitial autonomic dysfunction related to nicotine-mediated compensatory upregulation of sympathetic bias independent of endothelial injury induced by purported tobacco toxins. While hypertension is thought to cause atherosclerosis, the two conditions may instead represent independent consequences of autonomic dysfunction. The link between aging and atherosclerosis may operate through adventitial dysfunction induced by autonomic dysregulations. Exercise may ameliorate atherosclerosis by restoring adventitial autonomic function, thereby normalizing adventitial regulation of medial and intimal biology. Feed-forward adventitial vascular baroreceptor and chemoreceptor dysregulation may further exacerbate atherosclerosis as intimal plaque interferes with these sensors. Since penetrating external physical injury likely represented a dominant selective force during evolution, the adventitia may be preferentially equipped with sensors and response systems for vessel trauma. The convergent response of adrenergia, inflammation, and coagulation, which is adaptive for physical trauma, may be maladaptive today when different stressors trigger the cascade. Endoluminal therapies including atherectomy, angioplasty, and stent deployment involve balloon expansion that traumatizes all layers of the vessel wall. These interventions may paradoxically reinitiate the cascade of atherogenesis that begins with adventitial dysfunction and leads to restenosis. Methods to reduce adventitial trauma, a maladaptive trigger of adventitial dysfunction, may reduce the risk of restenosis. We envision novel mechanical and biopharmaceutical solutions that target the adventitia to prevent or treat atherosclerosis including novel drug delivery strategies, exo-stents that wrap vessels, and neuromodulation of vessels.

Mechanisms of Inducible Nitric Oxide Synthase–Mediated Vascular Dysfunction

Objective— Inducible nitric oxide synthase (iNOS) is expressed in arteries during inflammation and may contribute to vascular dysfunction. Effects of gene transfer of iNOS to carotid arteries were examined in vitro in the absence of systemic inflammation to allow examination of mechanisms by which iNOS impairs contraction and relaxation.

Methods and Results— After gene transfer of iNOS with an adenovirus (AdiNOS), constrictor responses to phenylephrine (PE) and U46619 were impaired. After AdiNOS, inhibition of soluble guanylate cyclase (sGC) with 1H-[1,2,4]oxadiazolo-[4,3,2]quinoxalin-1-one (ODQ) reduced the EC 50 for PE from 4.33±0.78 μmol/L to 1.15±0.43 μmol/L (mean±SEM). These results imply that iNOS impairs contraction by activation of the NO/cGMP pathway. Relaxation to acetylcholine (ACh) also was impaired after AdiNOS. Sepiapterin (300 μmol/L), the precursor for tetrahydrobiopterin (BH 4 ), improved relaxation to Ach. Because BH 4 is an essential cofactor for production of NO by both iNOS and endothelial nitric oxide synthase (eNOS), these results suggest that iNOS may reduce production of NO by eNOS by limiting availability of BH 4 . Next, we examined effects of expression of iNOS in endothelium and adventitia. Selective expression of iNOS in endothelium, but not adventitia, impaired contraction to phenylephrine and relaxation to acetylcholine.

Conclusions— We conclude that: (1) iNOS may impair contraction in part by activation of sGC; (2) iNOS impairs relaxation, at least in part, by limiting availability of BH 4 ; and (3) expression of iNOS in endothelium may be a more important mediator of vascular dysfunction than expression of iNOS in adventitia.

Role of the adventitia in the cyclic GMP-mediated relaxant effect of N-hydroxy-L-arginine in rat aorta

N(omega)-hydroxy-L-arginine (L-NOHA), the stable intermediate of the nitric oxide synthase (NOS)-catalyzed reaction, can induce NO/cyclic GMP-dependent relaxation in the rat aorta, in an endothelium- and NOS-independent manner. In this study, the role of the adventitia in the endothelium-independent effect of L-NOHA was investigated. Despite a decrease in norepinephrine (NE)-induced precontraction, adventitia removal in the rat aorta did not markedly alter the relaxant effect of forskolin, S-nitroso-N-acetylpenicillamine or glyceryl trinitrate. In contrast, both inhibition of NE-induced contraction and relaxation of NE-precontracted rings produced by L-NOHA were diminished in the absence of adventitia. Moreover, exposure to L-NOHA significantly enhanced the cyclic GMP level in the media of the aorta with, but not without adventitia. These findings demonstrate the role of the adventitia in the L-NOHA-induced decrease in tone and increase in cyclic GMP in the endothelium-denuded rat aorta. They suggest that NO or an NO-related compound formed from L-NOHA in the adventitia may produce paracrine effects.

Visceral Periadventitial Adipose Tissue Regulates Arterial Tone of Mesenteric Arteries

Periadventitial adipose tissue produces vasoactive substances that influence vascular contraction. Earlier studies addressed this issue in aorta, a vessel that does not contribute to peripheral vascular resistance. We tested the hypothesis that periadventitial adipose tissue modulates contraction of smaller arteries more relevant to blood pressure regulation. We studied mesenteric artery rings surrounded by periadventitial adipose tissue from adult male Sprague-Dawley rats. The contractile response to serotonin, phenylephrine, and endothelin I was markedly reduced in intact vessels compared with vessels without periadventitial fat. The contractile response to U46619 or depolarizing high K + -containing solutions (60 mmol/L) was similar in vessels with and without periadventitial fat. The K + channel opener cromakalim induced relaxation of vessels precontracted by serotonin but not by U46619 or high K + -containing solutions (60 mmol/L), suggesting that K + channels are involved. The intracellular membrane potential of smooth muscle cells was more hyperpolarized in intact vessels than in vessels without periadventitial fat. Both the anticontractile effect and membrane hyperpolarization of periadventitial fat were abolished by inhibition of delayed-rectifier K + (K v ) channels with 4-aminopyridine (2 mmol/L) or 3,4-diaminopyridine (1 mmol/L). Blocking other K + channels with glibenclamide (3 μmol/L), apamin (1 μmol/L), iberiotoxin (100 nmol/L), tetraethylammonium ions (1 mmol/L), tetrapentylammonium ions (10 μmol/L), or Ba 2+ (3 μmol/L) had no effect. Longitudinal removal of half the perivascular tissue reduced the anticontractile effect of fat by almost 50%, whereas removal of the endothelium had no effect. We suggest that visceral periadventitial adipose tissue controls mesenteric arterial tone by inducing vasorelaxation via K v channel activation in vascular smooth muscle cells.

Potential Interactions Among Vascular and Muscular Functional Compartments During Active Hyperemia

The increase in blood flow that accompanies the start of contractions (active hyperemia) is a complex phenomenon involving a fast phase in which blood flow increases quickly and then slows or decreases (seek phase) before stabilizing at a flow corresponding to the metabolic rate (matched phase). This pattern of blood flow change involves contributions from a flow-induced increase in flow, a response to short periods of occlusion or partial occlusion due to force generated by the muscle contraction, and metabolism. Even denervated, the vascular bed, which consists of endothelial cells, vascular smooth muscle cells, and an adventitial layer that has significant secretory potential, is able to coordinate the response pattern. Within the vascular wall, communication is possible bidirectionally across the wall and also along the wall in a retrograde or upstream direction. The signals involved, which range from endothelial cell products such as nitric oxide and endothelin to adenosine, a skeletal muscle metabolite, appear to be situation- and time-dependent. In addition to the communication potential within and along the vascular wall, signals from the vascular system are able to exert inotropic effects on mammalian skeletal muscle. Key words: bidirectional signaling, postcontraction hyperemia, flow-induced flow changes, signal plasticity

Constitutive expression of preproendothelin in the cardiac neural crest selectively promotes expansion of the adventitia of the great vessels in vivo

Cardiac neural crest cells are essential for normal development of the great vessels and the heart, giving rise to a range of cell types, including both neuronal and non-neuronal adventitial cells and smooth muscle. Endothelin (ET) signaling plays an important role in the development of cardiac neural crest cell lineages, yet the underlying mechanisms that act to control their migration, differentiation, and proliferation remain largely unclear. We examined the expression patterns of the receptor, ET(A), and the ET-specific converting enzyme, ECE-1, in the pharyngeal arches and great vessels of the developing chick embryo. In situ hybridization analysis revealed that, while ET(A) is expressed in the pharyngeal arch mesenchyme, populated by cardiac neural crest cells, ECE-1 expression is localized to the outermost ectodermal cells of the arches and then to the innermost endothelial cells of the great vessels. This dynamic pattern of expression suggests that only a subpopulation of neural crest cells in these regions is responsive to ET signaling at particular developmental time points. To test this, retroviral gene delivery was used to constitutively express preproET-1, a precursor of mature ET-1 ligand, in the cardiac neural crest. This resulted in a selective expansion of the outermost, adventitial cell population in the great vessels. In contrast, neither differentiation nor proliferation of neural crest-derived smooth muscle cells was significantly affected. These results suggest that constitutive expression of exogenous preproET-1 in the cardiac neural crest results in expansion restricted to an adventitial cell population of the developing great vessels.

Mechanics of the human femoral adventitia including the high-pressure response

Adventitial mechanics were studied on the basis of adventitial tube tests and associated stress analyses utilizing a thin-walled model. Inflation tests of 11 nonstenotic human femoral arteries (79.3 +/- 8.2 yr, means +/- SD) were performed during autopsy. Adventitial tubes were separated anatomically and underwent cyclic, quasistatic extension-inflation tests using physiological pressures and high pressures up to 100 kPa. Associated circumferential and axial stretches were typically <20%, indicating "adventitiosclerosis." Adventitias behaved nearly elastically for both loading domains, demonstrating high tensile strengths (>1 MPa). The anisotropic and strongly nonlinear mechanical responses were represented appropriately by two-dimensional Fung-type stored-energy functions. At physiological pressure (13.3 kPa), adventitias carry ~25% of the pressure load in situ, whereas their circumferential and axial stresses were similar to the total wall stresses (~50 kPa in both directions), supporting a "uniform stress hypothesis." At higher pressures, they became the mechanically predominant layer, carrying >50% of the pressure load. These significant load-carrying capabilities depended strongly on circumferential and axial in-vessel prestretches (mean values: 0.95 and 1.08). On the basis of these results, the mechanical role of the adventitia at physiological and hypertensive states and during balloon angioplasty was characterized.

Irbesartan lowers superoxide levels and increases nitric oxide bioavailability in blood vessels from spontaneously hypertensive stroke-prone rats

OBJECTIVE

To determine the effects of the angiotensin II receptor antagonist irbesartan, the calcium-channel blocker amlodipine, and hydrochlorothiazide/hydralazine on superoxide, NAD(P)H oxidase and nitric oxide bioavailability in spontaneously hypertensive stroke-prone rats (SHRSP).

METHODS

Drugs or vehicle were administered for 8 weeks to SHRSP and blood pressure was measured weekly by tail-cuff plethysmography. After 8 weeks, superoxide levels in carotid arteries and aortas were measured by lucigenin chemiluminescence and p22phox expression quantified by immunohistochemistry. In vitro the effects of exposure to drugs and vehicle for 30 min and 4 h on superoxide levels and nitric oxide bioavailability were examined. The latter was expressed as the increase in contractile responses of carotid arteries to phenylephrine in the presence of the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester(l-NAME).

RESULTS

In vivo irbesartan, amlodipine and hydrochlorothiazide/hydralazine produced similar falls in blood pressure, from 162 +/- 4 to 125 +/- 5, 132 +/- 4 and 131 +/- 6 mmHg, respectively, but irbesartan caused a greater reduction in superoxide and p22phox; superoxide levels in carotid arteries being 3.1 +/- 0.3, 1.1 +/- 0.2, 1.9 +/- 0.3 and 2.0 +/- 0.3 nmoles/mg per min, respectively. In vitro 4 h exposure to irbesartan decreased superoxide levels in the aorta from 2.08 +/- 0.68 to 1.48 +/- 0.62 nmoles/mg per min and increased nitric oxide bioavailability in carotid arteries. Neither 30 min incubation with irbesartan nor 4 h with amlodipine or hydrochlorothiazide/hydralazine altered superoxide levels.

CONCLUSIONS

These studies support the hypothesis that AT1 receptor blockade has beneficial effects on superoxide production and nitric oxide bioavailability above that of other classes of antihypertensive agents. Reduced expression of components of the NAD(P)H oxidase may contribute to these effects.