Adenovector-mediated gene transfer of active transforming growth factor-beta1 induces prolonged severe fibrosis in rat lung

Transforming growth factor (TGF)-beta1 has been implicated in the pathogenesis of fibrosis based upon its matrix-inducing effects on stromal cells in vitro, and studies demonstrating increased expression of total TGF-beta1 in fibrotic tissues from a variety of organs. The precise role in vivo of this cytokine in both its latent and active forms, however, remains unclear. Using replication-deficient adenovirus vectors to transfer the cDNA of porcine TGF-beta1 to rat lung, we have been able to study the effect of TGF-beta1 protein in the respiratory tract directly. We have demonstrated that transient overexpression of active, but not latent, TGF-beta1 resulted in prolonged and severe interstitial and pleural fibrosis characterized by extensive deposition of the extracellular matrix (ECM) proteins collagen, fibronectin, and elastin, and by emergence of cells with the myofibroblast phenotype. These results illustrate the role of TGF-beta1 and the importance of its activation in the pulmonary fibrotic process, and suggest that targeting active TGF-beta1 and steps involved in TGF-beta1 activation are likely to be valuable antifibrogenic therapeutic strategies. This new and versatile model of pulmonary fibrosis can be used to study such therapies.

PDGF-A signaling is a critical event in lung alveolar myofibroblast development and alveogenesis

A mouse platelet-derived growth factor A chain (PDGF-A) null allele is shown to be homozygous lethal, with two distinct restriction points, one prenatally before E10 and one postnatally. Postnatally surviving PDGF-A-deficient mice develop lung emphysema secondary to the failure of alveolar septation. This is apparently caused by the loss of alveolar myofibroblasts and associated elastin fiber deposits. PDGF alpha receptor-positive cells in the lung having the location of putative alveolar myofibroblast progenitors were specifically absent in PDGF-A null mutants. We conclude that PDGF-A is crucial for alveolar myofibroblast ontogeny. We have previously shown that PDGF-B is required in the ontogeny of kidney mesangial cells. The PDGFs therefore appear to regulate the generation of specific populations of myofibroblasts during mammalian development. The two PDGF null phenotypes also reveal analogous morphogenetic functions for myofibroblast-type cells in lung and kidney organogenesis.

Intravascular ultrasound imaging: in vitro validation and pathologic correlation

Intravascular ultrasound imaging is a new method in which high resolution images of the arterial wall are obtained with use of a catheter placed within an artery. An in vitro Plexiglas well model was used to validate measurements of the luminal area, and an excellent correlation was obtained. One hundred thirty segments of fresh peripheral arteries underwent ultrasound imaging and the findings were compared with the corresponding histopathologic sections. Luminal areas determined with ultrasound imaging correlated well with those calculated from microscopic slides (r = 0.98). Three patterns were identified on the ultrasound images: 1) distinct interface between media and adventitia, 2) indistinct interface between media and adventitia but different echo density layers, and 3) diffuse homogeneous appearance. The types of patterns depended on the relative composition of the media and adventitia. Calcification of intimal plaque obscured underlying structures. Atherosclerotic plaque was readily visualized but could not always be differentiated from the underlying media.

LRP: role in vascular wall integrity and protection from atherosclerosis

Vascular smooth muscle cell (SMC) proliferation and migration are important events in the development of atherosclerosis. The low-density lipoprotein receptor-related protein (LRP1) mediates suppression of SMC migration induced by platelet-derived growth factor (PDGF). Here we show that LRP1 forms a complex with the PDGF receptor (PDGFR). Inactivation of LRP1 in vascular SMCs of mice causes PDGFR overexpression and abnormal activation of PDGFR signaling, resulting in disruption of the elastic layer, SMC proliferation, aneurysm formation, and marked susceptibility to cholesterol-induced atherosclerosis. The development of these abnormalities was reduced by treatment with Gleevec, an inhibitor of PDGF signaling. Thus, LRP1 has a pivotal role in protecting vascular wall integrity and preventing atherosclerosis by controlling PDGFR activation.

Marked longevity of human lung parenchymal elastic fibers deduced from prevalence of D-aspartate and nuclear weapons-related radiocarbon

Normal structure and function of the lung parenchyma depend upon elastic fibers. Amorphous elastin is biochemically stable in vitro, and may provide a metabolically stable structural framework for the lung parenchyma. To test the metabolic stability of elastin in the normal human lung parenchyma, we have (a) estimated the time elapsed since the synthesis of the protein through measurement of aspartic acid racemization and (b) modeled the elastin turnover through measurement of the prevalence of nuclear weapons-related 14C. Elastin purified by a new technique from normal lung parenchyma was hydrolyzed; then the prevalences of D-aspartate and 14C were measured by gas chromatography and accelerator-mass spectrometry, respectively. D-aspartate increased linearly with age; Kasp (1.76 x 10(-3) yr(-1) was similar to that previously found for extraordinarily stable human tissues, indicating that the age of lung parenchymal elastin corresponded with the age of the subject. Radiocarbon prevalence data also were consistent with extraordinary metabolic stability of elastin; the calculated mean carbon residence time in elastin was 74 yr (95% confidence limits, 40-174 yr). These results indicate that airspace enlargement characteristic of "aging lung" is not associated with appreciable new synthesis of lung parenchymal elastin. The present study provides the first tissue-specific evaluation of turnover of an extracellular matrix component in humans and underscores the potential importance of elastin for maintenance of normal lung structure. Most importantly, the present work provides a foundation for strategies to directly evaluate extracellular matrix injury and repair in diseases of lung (especially pulmonary emphysema), vascular tissue, and skin.

A lamellar unit of aortic medial structure and function in mammals

The close association of elastin, collagen, and smooth muscle in the mammalian aortic media results in viscoelastic properties that account for many of its static and dynamic mechanical features. The structural components of the media are precisely oriented in concentric layers, or lamellar units, of fairly uniform composition. A comparative study of the adult thoracic aorta in 10 mammalian species, including 15 canine breeds, showed that the number of lamellar units in the media of adult mammalian aortas is very nearly proportional to aortic radius regardless of species or variations in measured wall thickness. Estimated wall tensions ranged from 7,820 dynes/cm in a 28-g mouse to 203,000 dynes/cm in a 200,000-g sow, but the average tension per lamellar unit of an aortic media was remarkably constant regardless of species, ranging from 1,090 to 3,010 dynes/cm. The findings suggest that the elastin lamella and the contents of its adjacent interlamellar zone represent the unit of structure and function of the mammalian aortic wall.

Ectopic induction of tendon and ligament in rats by growth and differentiation factors 5, 6, and 7, members of the TGF-beta gene family

Little is known about the regulatory signals involved in tendon and ligament formation, and this lack of understanding has hindered attempts to develop biologically based therapies for tendon and ligament repair. Here we report that growth and differentiation factors (GDFs) 5, 6, and 7, members of the TGF-beta gene superfamily that are most related to the bone morphogenetic proteins, induce neotendon/ligament formation when implanted at ectopic sites in vivo. Analysis of tissue induced by GDF-5, 6, or 7, containing implants by currently available morphological and molecular criteria used to characterize tendon and ligament, adds further evidence to the idea that these GDFs act as signaling molecules during embryonic tendon/ligament formation. In addition, comparative in situ localizations of the GDF-5, 6, and 7 mRNAs suggest that these molecules are important regulatory components of synovial joint morphogenesis.

Chemotactic activity of elastin-derived peptides

Elastin-derived peptides, produced by digesting human aortic elastin and bovine ligament elastin with human neutrophil elastase, were tested for chemotactic activity. At 100 micrograms protein/ml, elastin digests were nearly as active for monocytes as saturating amounts of complement-derived chemotactic activity. Neutrophils and alveolar macrophages showed less response to elastin peptidces than did monocytes. Fractionation of the digests by gel filtration chromatography disclosed that maximal chemotactic activity eluted in fractions corresponding to 14,000-20,000 mol wt containing most of the desmosine cross-links in the digests. Whole human serum and rabbit anti-elastin immunoglobulin inhibited the chemotactic activity. Purified desmosine also showed chemotactic activity for monocytes, maximal at 10 nM. These findings suggest that elastin-degradation products enriched in cross-linking regions recruit inflammatory cells in vivo and that elastin proteolysis, characteristic of emphysema, may be a signal for recruitment of mononuclear phagocytes into the lungs.

Vascular matrix remodeling in patients with bicuspid aortic valve malformations: implications for aortic dilatation

BACKGROUND

Patients with bicuspid aortic valve malformations are at an increased risk of aortic dilatation, aneurysm formation, and dissection. Vascular tissues with deficient fibrillin-1 microfibrils release matrix metalloproteinases, enzymes that weaken the vessel wall by degrading elastic matrix components. In bicuspid aortic valve disease a deficiency of fibrillin-1 and increased matrix metalloproteinase matrix degradation might result in aortic degeneration and dilatation.

METHODS

Samples of the pulmonary artery and aorta were obtained from surgical patients with bicuspid aortic valves (n = 21) and tricuspid aortic valves (n = 16).

RESULTS

Fibrillin-1 content was reduced in bicuspid aortic valve aortas compared with that seen in tricuspid aortic valve aortas (P =.001), whereas the associated matrix components, elastin and collagen, were unchanged (P =.51 and P =.21). Reductions of aortic fibrillin-1 content were independent of valve function and patient age. Compared with tricuspid aortic valve aorta, matrix metalloproteinase 2 activity was increased more than 2-fold in bicuspid aortic valve aortas (P =.04) and correlated positively with aortic diameter (r = 0.74, P =.05). Matrix metalloproteinase 9 activity was not significantly different. Fibrillin-1 content was also reduced in the pulmonary arteries of patients with bicuspid aortic valves (P =.06), suggesting a systemic deficiency of fibrillin-1. Promatrix metalloproteinase 2 was increased (P =.04), reflecting an increased production of matrix metalloproteinase 2 in these fibrillin-1-deficient tissues, whereas active matrix metalloproteinase 2 and matrix metalloproteinase 9 species were unchanged, and correspondingly, the pulmonary arteries were not dilated.

CONCLUSIONS

Deficient fibrillin-1 content in the vasculature of patients with bicuspid aortic valves might trigger matrix metalloproteinase production, leading to matrix disruption and dilatation. This process of vascular matrix remodeling in patients with bicuspid aortic valves offers novel therapeutic targets to prevent the aortic degeneration and dilatation characteristic of this disease.

Human semilunar cardiac valve remodeling by activated cells from fetus to adult: implications for postnatal adaptation, pathology, and tissue engineering

BACKGROUND

The evolution of cell phenotypes and matrix architecture in cardiac valves during fetal maturation and postnatal adaptation through senescence remains unexplored.

METHODS AND RESULTS

We hypothesized that valvular interstitial (VIC) and endothelial cell (VEC) phenotypes, critical for maintaining valve function, change throughout life in response to environmental stimuli. We performed quantitative histological assessment of 91 human semilunar valves obtained from fetuses at 14 to 19 and 20 to 39 weeks' gestation; neonates minutes to 30 days old; children aged 2 to 16 years; and adults. A trilaminar architecture appeared by 36 weeks of gestation but remained rudimentary compared with that of adult valves. VECs expressed an activated phenotype throughout fetal development. VIC density, proliferation, and apoptosis were significantly higher in fetal than adult valves. Pulmonary and aortic fetal VICs showed an activated myofibroblast-like phenotype (alpha-actin expression), abundant embryonic myosin, and matrix metalloproteinase-collagenases, which indicates an immature/activated phenotype engaged in matrix remodeling versus a quiescent fibroblast-like phenotype in adults. At birth, the abrupt change from fetal to neonatal circulation was associated with a greater number of alpha-actin-positive VICs in neonatal aortic versus pulmonary valves. Collagen content increased from early to late fetal stages but was subsequently unchanged, whereas elastin significantly increased postnatally. Collagen fiber color analysis revealed a progressive temporal decrease in thin fibers and a corresponding increase in thick fibers. Additionally, collagen fibers were more aligned in adult than fetal valves.

CONCLUSIONS

Fetal valves possess a dynamic/adaptive structure and contain cells with an activated/immature phenotype. During postnatal life, activated cells gradually become quiescent, whereas collagen matures, which suggests a progressive, environmentally mediated adaptation.

The smooth muscle cell. I. In vivo synthesis of connective tissue proteins

These studies have examined the ability of smooth muscle cells from developing aorta of the prepubertal rat to utilize amino acids in the synthesis and secretion of connective tissue proteins. Prepubertal rats, previously given either an alcohol carrier or estradiol-17-beta, were each given an intravenous injection of proline-(3)H. The animals were sacrificed after 15 and 30 min, and 4 hr. Light and electron microscope radioautographs of the aortic smooth muscle and of the myometrial cells demonstrated that the aortic cells, in both groups of animals, and the myometrial cells, in the estrogen-stimulated animals, took up the proline and rapidly secreted it in both collagen and elastic fibers within 4 hr. In contrast, the myometrial cells of the nonstimulated animal took up relatively small amounts of proline and retained most of the amino acid within the cells. Electron microscope radioautographs demonstrated that the organelles involved in this activity were the rough endoplasmic reticulum and Golgi complex together with peripheral elements, presumed to be small vesicles. These studies have demonstrated that the smooth muscle cells of the developing aorta and of the estrogen-stimulated myometrium have a capacity to synthesize and secrete proteins associated with the extracellular connective tissue matrix.

Collagenase expression in the lungs of transgenic mice causes pulmonary emphysema

Transgenic mice were generated that expressed a human collagenase transgene in their lungs under the direction of the haptoglobin promoter. Histological analysis demonstrated disruption of the alveolar walls and coalescence of the alveolar spaces with no evidence of fibrosis or inflammation. This pathology is strikingly similar to the morphological changes observed in human emphysema and therefore implicates interstitial collagenase as a possible etiological agent in the disease process. Although elastase has been proposed as the primary enzyme responsible for emphysematous lung damage, this study provides evidence that other extracellular matrix proteases could play a role in emphysema. In addition, these transgenic mice are a defined genetic animal model system to study the pathogenesis of emphysema.

Long-term effects of hypertension on the rat aortic wall and their relation to concurrent aging changes. Morphological and chemical studies

The effects of long-term (16 months) hypertension on the thoracic aorta of male rats were compared to previously reported short-term (2.5 months) changes and to concurrent aging changes. Hypertension was produced by clipping a renal artery. Although short-term hypertension was characterized by a disproportionate increase in noncollagenous alkali-soluble proteins, which have been attributed primarily to vascular smooth muscle, with long-term hypertension there was no further increase in these proteins but instead there were striking increases in mural accumulations of elastin and collagen. Chronically elevated wall tension in hypertensive vessels was associated with a progressive increase in wall thickness which resulted in a value for wall stress no different from that of control vessels. Concurrent aging changes were qualitatively similar to, but much less pronounced than, those seen with hypertension and were attributed to an increase in wall tension in controls resulting from a combination of significant increases in diameter and systolic blood pressure with age. This study of the interaction of vessel structure and function has revealed common features of what appears to be a diverse group of vascular alterations.

Elastin degradation in abdominal aortic aneurysms

Histological sections through the walls of abdominal aortic aneurysms showed scarce and disrupted elastic tissue. The elastin content of the aneurysmal aortic media was only 8.1 +/- 3.2% dry defatted weight (n = 11). The elastin content of grossly normal age and anatomically matched aortic media was 35.0 +/- 3.2% dry weight (n = 4) and the elastin content of severely atherosclerotic, stenosed infrarenal aortic media was 22.0 +/- 7.2% dry weight (n = 6). There was an inverse correlation of elastin content with the elastinolytic activity of aortic media homogenates, r = -0.78. Elastase activity, measured by the hydrolysis of [3H]elastin, was highest in aneurysmal aortic homogenates, 92.1 +/- 43.7 U/mg protein (n = 18), falling to 46.9 +/- 13.3 U/mg protein (n = 13) in severely stenosed atherosclerotic aortic homogenates and 35.5 +/- 11.9 U/mg (n = 6) in grossly normal aortic homogenates. The elastinolytic activity of stenotic aorta contained leukocyte elastase as an important component. In aneurysmal homogenates leukocyte elastase was also found but the increased elastase activity resulted from a protease(s) (Mr 95,000) extracted in 2 M urea, having minimal specificity for alanyl bonds and no immunological cross-reactivity with leukocyte elastase.

Response of the rat aortic media to hypertension. Morphological and chemical studies

Clinical and experimental studies indicate that hypertension accelerates the development of arteriosclerosis. Morphological and chemical studies of the distended rat thoracic aorta were undertaken to define the structural and compositional alterations of the media which accompany hypertension and to relate these changes to increases in calculated medial stress. An 8-week period of hypertension was associated with significantly greater diameter, medial thickness, and cross-sectional area of the media of the thoracic aorta than in normotensive animals. Calculated wall tension was significantly higher in hypertensive animals, but the number of medial lamellar units was not greater than that usual in normotensive animals; this resulted in a strikingly elevated value for calculated tension per medial lamellar unit for the aortas of hypertensive animals. A highly significant linear relation was found between total tension and cross-sectional area of the media of the same segment. In addition, the absolute amounts of both medial elastin and collagen were increased in hypertensive animals; however, the percent of these elements remained essentially constant, indicating little change in the composition of aortic tissue. Increments in both fibrous proteins were linearly related to increases in calculated mural stress, and medial accumulations of elastin and collagen proceeded at similar rates. These findings demonstrate a linear relation among vessel dimensions and amounts of medial elastin and collagen and calculated wall tension.

The induction of pulmonary emphysema with human leukocyte elastase

Purified human leukocyte elastase was injected into the tracheas of 46 hamsters. Thirteen animals died spontaneously within 1 week, with extensive lung hemorrhage. The elastin content of the lungs was only slightly less than control values 3 hours after injection. At 2 months, the lungs of the remaining animals showed mild, patchy emphysema and morphometric changes consistent with emphysema. These results contrasted with the effects of a similar elastolytic dose of pancreatic elastase administered to 26 other hamsters in that only one animal died spontaneously, the lung elastin content 3 hours after injection was substantially decreased, and severe emphysema was present 2 months later. Leukocyte elastase appears to be capable of causing emphysema; but unlike pancreatic elastase, leukocyte elastase produces emphysema that is mild, even at a dose sufficient to produce intense lung hemorrhage and a high mortality.

Local overexpression of TIMP-1 prevents aortic aneurysm degeneration and rupture in a rat model

Although matrix metalloproteinases (MMPs) are expressed in abundance in arterial aneurysms, their contribution to arterial wall degeneration, dilation, and rupture has not been determined. We investigated MMP function in a rat model of aneurysm associated with arterial dilation, elastin loss, medial invasion by mononuclear inflammatory cells, and MMP upregulation. Rupture was correlated with increased gelatinase B (MMP-9) and activated gelatinase A (MMP-2). Syngeneic rat smooth muscle cells retrovirally transfected with tissue inhibitor of matrix metalloproteinases (TIMP)-1 cDNA (LTSN) or with the vector alone as a control (LXSN) were seeded onto the luminal surface of the vessels. The seeding of LTSN cells resulted in TIMP-1 local overexpression. The seeding with LTSN cells, but not LXSN cells, decreased MMP-9, activated MMP-2 and 28-kD caseinase and elastase activity, preserved elastin in the media, and prevented aneurysmal degeneration and rupture. We conclude that MMP overexpression is responsible for aneurysmal degeneration and rupture in this rat model and that local pharmacological blockade might be a reasonable strategy for controlling the formation of aneurysms in humans.

Tissue elasticity and the ageing elastic fibre

The ability of elastic tissues to deform under physiological forces and to subsequently release stored energy to drive passive recoil is vital to the function of many dynamic tissues. Within vertebrates, elastic fibres allow arteries and lungs to expand and contract, thus controlling variations in blood pressure and returning the pulmonary system to a resting state. Elastic fibres are composite structures composed of a cross-linked elastin core and an outer layer of fibrillin microfibrils. These two components perform distinct roles; elastin stores energy and drives passive recoil, whilst fibrillin microfibrils direct elastogenesis, mediate cell signalling, maintain tissue homeostasis via TGFβ sequestration and potentially act to reinforce the elastic fibre. In many tissues reduced elasticity, as a result of compromised elastic fibre function, becomes increasingly prevalent with age and contributes significantly to the burden of human morbidity and mortality. This review considers how the unique molecular structure, tissue distribution and longevity of elastic fibres pre-disposes these abundant extracellular matrix structures to the accumulation of damage in ageing dermal, pulmonary and vascular tissues. As compromised elasticity is a common feature of ageing dynamic tissues, the development of strategies to prevent, limit or reverse this loss of function will play a key role in reducing age-related morbidity and mortality.

Elastic fiber production in cardiovascular tissue-equivalents

Elastic fiber incorporation is critical to the success of tissue-engineered arteries and heart valves. Elastic fibers have not yet been observed in tissue-engineered replacements fabricated in vitro with smooth muscle cells. Here, rat smooth muscle cells (SMC) or human dermal fibroblasts (HDF) remodeled collagen or fibrin gels for 4 weeks as the basis for a completely biological cardiovascular tissue replacement. Immunolabeling, alkaline extraction and amino acid analysis identified and quantified elastin. Organized elastic fibers formed when neonatal SMC were cultured in fibrin gel. Fibrillin-1 deposition occurred but elastin was detected in regions without fibrillin-1, indicating that a microfibril template is not required for elastic fiber formation within fibrin. Collagen did not support substantial elastogenesis by SMC. The quantity of crosslinked elastic fibers was enhanced by treatment with TGF-beta1 and insulin, concomitant with increased collagen production. These additives overcame ascorbate's inhibition of elastogenesis in fibrin. The elastic fibers that formed in fibrin treated with TGF-beta1 and insulin contained crosslinks, as evidenced by the presence of desmosine and an altered elastin labeling pattern when beta-aminopropionitrile (BAPN) was added. These findings indicate that in vitro elastogenesis can be achieved in tissue engineering applications, and they suggest a physiologically relevant model system for the study of three-dimensional elastic structures.

Histologic and rheologic characterization of vocal fold scarring

Scarring of the vocal fold causes considerable dysphonia and presents significant treatment challenges. A rabbit model was developed to investigate the histologic ultrastructure and rheologic properties of the scarred vocal fold lamina propria. Eleven rabbit larynges were scarred by means of forcep biopsy. Sixty days postoperatively, the rabbits were sacrificed and their vocal folds were harvested. Histological analysis of the scarred and normal lamina propria was completed for collagen, procollagen, elastin, and hyaluronic acid. Linear viscoelastic shear properties of the tissues were also measured, including elastic shear modulus and dynamic viscosity. Compared to normal vocal fold lamina propria, scarred tissues demonstrated significantly less collagen, an increase in procollagen, and a decrease in elastin. Rheologically, both elastic shear modulus and dynamic viscosity were significantly higher for the scarred tissues. Increased stiffness and viscosity do not appear to result from an increase in collagen, but rather appear to be related to the presence of new, disorganized collagen scaffolding. Results are interpreted in terms of the possible role of interstitial proteins in the etiology of increased stiffness and viscosity, which requires further investigation. This animal model should allow for systematic future investigations of vocal fold scarring and its treatment.

The composition and mechanical properties of abdominal aortic aneurysms

PURPOSE

The composition and mechanical properties of abdominal aortic aneurysms (AAAs) were studied.

METHODS

Stereologic study was used to measure volume fractions of the components of the aortic wall. Histochemical methods with picrosirus red and safranin O were developed to differentiate collagen from ground substance because they are difficult to distinguish from each other on histologic sections. Uniaxial tensile stress tests were carried out on a tensile-testing machine, and a stress-strain curve was plotted for each sample to study the mechanical properties of AAAs. The curves were fitted exponentially so sigma = aeb epsilon, where sigma is stress, epsilon is strain, and a and b are parameters.

RESULTS

In aneurysms (n = 8) the volume fraction of elastin was decreased from 22.7% +/- 5.7% to 2.4% +/- 2.2%, and the volume fraction of smooth muscle cells was decreased from 22.6% +/- 5.5% to 2.2% +/- 2.0%, whereas the volume fraction of collagen and ground substance combined was increased from 54.8% +/- 4.5% to 95.6% +/- 2.5% compared with nonaneurysmal aortas (n = 8). There was no significant difference (p > 0.05) in the ratio of collagen to ground substance (2.1 +/- 0.5 vs 2.0 +/- 0.4) between AAAs and nonaneurysmal aortas. The elastic diagrams showed that AAAs (n = 7) are less distensible and stiffer than nonaneurysmal aortas (n = 5). Parameter a was unchanged (p > 0.5), but parameter b was significantly greater (p < 0.002) for aneurysmal aortas.

CONCLUSIONS

Both the composition and mechanical properties of AAAs are different from those of nonaneurysmal aortas. The aneurysms were stiffer, and the volume fractions of collagen and ground substance were increased, whereas the volume fractions of elastin and muscle were decreased in aneurysms.

Chronic blockade of AT2-subtype receptors prevents the effect of angiotensin II on the rat vascular structure

Angiotensin II (Ang II) is both a vasoactive and a potent growth-promoting factor for vascular smooth muscle cells. Little is known about the in vivo contribution of AT1 and AT2 receptor activation to the biological action of Ang II. Therefore, we investigated the effect of AT1 or AT2 subtype receptor chronic blockade by losartan or PD123319 on the vascular hypertrophy in rats with Ang II-induced hypertension. Normotensive rats received for 3 wk subcutaneous infusions of Ang II (120 ng/kg per min), or Ang II + PD 123319 (30 mg/kg per d), or Ang II + losartan (10 mg/kg per d) or PD 123319 alone, and were compared with control animals. In normotensive animals, chronic blockade of AT2 receptors did not affect the plasma level of angiotensin II and the vascular reactivity to angiotensin II mediated by the AT1 receptor. Chronic blockade of AT1I in rats receiving Ang II resulted in normal arterial pressure, but it induced significant aortic hypertrophy and fibrosis. Chronic blockade of AT2 receptors in Ang II-induced hypertensive rats had no effect on arterial pressure, but antagonized the effect of Ang II on arterial hypertrophy and fibrosis, suggesting that in vivo vasotrophic effects of Ang II are at least partially mediated via AT2 subtype receptors.