Nonenzymatic glycation of fibronectin impairs adhesive and proliferative properties of human vascular smooth muscle cells

Nonenzymatic glycation of proteins is involved in the pathogenesis of diabetes vascular complications. Extracellular matrix proteins are a prominent target for nonenzymatic glycation because of their slow turnover rates. The aim of this study was to investigate the influence of human fibronectin (F) nonenzymatic glycation on adhesion and proliferation of cultured human vascular smooth muscle cells (hVSMC). Incubation of human F with 500 mmol/L D-glucose at 37 degrees C induced a time-dependent increase in fluorescence detectable at 440 nm after excitation at 363 nm. Nonenzymatic glycation did not affect binding of F itself to the plates. Adhesion of hVSMC to F increased with the increase of incubation time of the cells on the protein from 30 minutes up to 120 minutes and remained stable thereafter. Adhesion to glycated fibronectin (GF) was reduced in comparison to control F at all the different adhesion times. Adhesion of hVSMC to GF was reduced when F was exposed to glucose for 4, 9, or 28 days (P=.0417 to .0025), but not when F was exposed for 1 day. Adhesion of hVSMC to GF was reduced compared with adhesion to nonglycated F at all coating concentrations from 0.2 to 10 micrograms/mL (P=.05 to .014). Thus, nonenzymatic glycation of F impairs adhesion of hVSMC in vitro. Proliferation of hVSMC on F increased with increasing concentrations of the protein as coating agent (ANOVA:P<.0001 for both nonglycated F and GF). Proliferation with F glycated for 4, 9, and 28 days was reduced at concentrations of 1, 3, and 10 micrograms/mL as compared with proliferation with nonglycated F (P=.0253 to .0001). Proliferation on F glycated for only 1 day was not significantly reduced. When the number of hVSMC plated on control F was reduced by 25% to take into account the reduced adhesion, the number of cells that proliferated on F was still reduced. In conclusion, nonenzymatic glycation of F impairs adhesive and proliferative properties of hVSMC.

Effective written communication in biomedical sciences

The written word is the biomedical scientist's most important and most enduring communication tool. Nevertheless, the development of writing skills receives little attention in most scientific disciplines and the ability to conduct research is often viewed as more important than the ability to communicate the results of that research. Consequently, many scientists lack the writing skills necessary to effectively convey essential aspects of their research. In this paper, we will discuss the importance of good writing skills, give examples of common mistakes that are made in biomedical science writing and offer suggestions on how to improve written communication.

Escherichia coli O157:H7 restriction pattern recognition by artificial neural network

An artificial neural network model for the recognition of Escherichia coli O157:H7 restriction patterns was designed. In the training phase, images of two classes of E. coli isolates (O157:H7 and non-O157:H7) were digitized and transmitted to the neural network. The system was then tested for recognition of images not included in the training set. Promising results were achieved with the designed network configuration, providing a basis for further study. This application of a new generation of computation technology serves as an example of its usefulness in microbiology.

Effects of electrocardiograph frequency filters on P-QRS-T amplitudes of the feline electrocardiogram

OBJECTIVE--To determine whether standard manual frequency filters in the ON and OFF settings affected P-QRS-T voltages, discover whether recorded P-QRS-T voltages vary between commercial electrocardiographs, assess effects of frequency filters on base-line artifact, and evaluate ECG frequency content by high-fidelity recordings subjected to digital filters with variable frequencies. DESIGN--Sequential 10-lead ECG were recorded in 30 cats, using 3 commercial electrocardiographs to assess effects of manual frequency filters on the P-QRS-T wave forms. Three clinically normal cats were evaluated for ECG frequency content. ANIMALS--Thirty cats (13 with hypertrophic cardiomyopathy; 4 with restrictive cardiomyopathy; 3 hyperthyroid; 1 with ventricular septal defect; 1 with aortic stenosis; and 8 with no detectable cardiovascular disease). Three additional clinically normal cats were studied for effects of frequency filters on the ECG frequency content. PROCEDURES--Ten-lead ECG were recorded on each cat by use of 3 commercial electrocardiographs sequentially. For each machine, a recording was made with manual filters ON, immediately followed by a recording with manual filters OFF. High-fidelity lead-II ECG recordings were made with filters set with their rolloff frequency at 0.1 Hz and 3.0 kHz; output voltage (0.2 mV/V) was fed to an analog-to-digital converter, then to attendant software, which sampled the signal at 6 kHz with a 12-bit sampler, and were digitally filtered at various corner frequencies. RESULTS--Voltages recorded by all 3 electrocardiographs were greatest when filters were OFF (most prominent on R- and S-wave voltages). In all recorded leads, R-wave voltage was significantly greater when filters were OFF than ON. Comparison of voltages indicated significant (P < 0.05) differences between R-wave voltages recorded in all leads with manual filters ON, but not with filters OFF. With filters ON, each electrocardiograph produced a smaller percentage of recordings with moderate to severe baseline artifact than with filters OFF. R-Wave amplitudes of high-fidelity lead-II ECG were significantly decreased with digital filters set at corner frequencies < 150 Hz. CONCLUSIONS--Significant (P < 0.05) voltage attenuation was recorded by each of the 3 commercial electrocardiographs when frequency filters were ON, compared with OFF. Comparison of waveform voltages among electrocardiographs with filters ON indicated significant variation in R-wave amplitudes in all leads. With manual filters ON, each electrocardiograph recorded a smaller percentage of recordings with baseline artifact than with filters OFF. Substantial frequency components > or = 150 Hz are present in the feline ECG waveform. Thus, filters with frequencies < 150 Hz markedly attenuate the feline R wave. CLINICAL RELEVANCE--Attenuation of feline ECG signals occurs with use of commercial electrocardiographs and varies greatly between manufacturers. This is attributable largely to internal manual frequency filters. These consequences may be important when applying standard feline reference values or when equivocal voltage measurements are recorded.

Low- and high-density lipoproteins as mitogenic factors for vascular smooth muscle cells: individual, additive and synergistic effects

The mitogenic activities of low (LDL)- and high (HDL)-density lipoproteins have been examined in cultures of human vascular smooth muscle cells (VSMC). LDL and HDL3 dose-dependently (EC50 values approximately 50 micrograms/ml) stimulated DNA and protein synthesis ([3H]-thymidine and [3H]-leucine incorporation, respectively) in the absence of exogenously added mitogens. The synthetic responses of VSMC to combinations of LDL and HDL3 were additive, indicating that each lipoprotein mediates discrete effects. LDL or HDL3 promoted VSMC proliferation under strict mitogen-free conditions, but this growth response was not sustained. VSMC exposed to combinations of lipoproteins (either LDL or HDL3) and growth factors (either PDGF-BB, EGF, bFGF or IGF) exhibited synergistic DNA synthesis responses. In the combined presence of PDGF-BB and either LDL or HDL3, VSMC proliferation was sustained. Anionized lipoprotein preparations (oxidized, acetylated, carbamylated or malonimylated) also stimulated DNA and protein synthesis. Since the antioxidant beta-hydroxylated toluene did not block the effect of native LDL on DNA synthesis, and fucoidin, a specific competitor for the 'scavenger' receptor, did not inhibit oxidized LDL-induced DNA synthesis, activation of mitogenic signals by lipoproteins does not depend on lipid peroxidation. Rather, the apparent intrinsic mitogenic potential of lipoproteins may depend upon their direct activation of replication-coupled signal transduction systems.

Endothelium-modulated proliferation of medial smooth muscle cells: influence of angiotensin II and converting enzyme inhibition

This study investigated the role of the endothelium and angiotensin II (Ang II) in regulating medial smooth muscle cell (SMC) proliferation. [3H]-thymidine incorporation into medial SMC of rat arteries was examined in vivo, using ballooned rat carotid arteries, as well as in vitro, using cultures of aortic tissue rings (organoids). In vivo, maximal medial [3H]-thymidine incorporation occurred within 3 days post-ballooning. In endothelium-denuded organoids, maximum medial DNA synthesis was achieved after 7 days of culture. [3H]-thymidine-labelling of SMC in intact organoids (with endothelium) increased minimally during culture, indicating that the endothelium provided protection with respect to medial proliferation under basal conditions (culture in the presence of 1% plasma-derived serum). Inclusion of 10(-7) M Ang II significantly elevated medial [3H]-thymidine incorporation above that in control cultures. The stimulatory effect of Ang II was much more pronounced in intact organoids that in endothelium-denuded organoids, indicating synergistic growth regulation by Ang II and endothelium-derived factors. When organoids were cultured in the combined presence of Ang II and the ACE inhibitor cilazaprilat, labelling indices of intact organoids were also significantly increased above control, but to a lower level than those obtained in the presence of Ang II alone. However, for endothelium-denuded organoids, medial [3H]-thymidine incorporation in the combined presence of Ang II and cilazaprilat was not significantly different from that in untreated controls. Thus, cilazaprilat exerts both endothelium-dependent and endothelium-independent negative regulatory effects on medial SMC proliferation.

Functional aspects of vascular tenascin-C expression

The arterial tenascin C expression in vivo and in vitro has been studied using immunohistochemistry. The functional relevance of localized tenascin C expression was assessed in vitro using various human cell types involved in the progression of vascular disease. Normotensive and hypertensive rats exhibited age-dependent patterns of vascular (aorta) tenascin expression, but the lumen-to-media-directed progression of tenascin induction was accelerated in hypertensive rats. Tenascin-rich neointimal lesions (spontaneous) were observed at branching sites of aorta from aged (80 weeks) hypertensive rats. Subendothelial tenascin foci contained lipid-laden smooth muscle cells and monocytes/macrophages. Medial tenascin foci encaged smooth muscle cells which synthesized DNA. Tenascin was expressed both in vivo and in vitro by endothelial and smooth muscle cells but not by monocytes/macrophages; angiotensin II, oxidized-low density lipoprotein and transforming growth factor beta 1 induced expression of tenascin transcripts and glycoprotein in vitro. Endothelial and smooth muscle cells, but not monocytes, adhered to tenascin substrata. Tenascin reduced focal adhesion integrity in confluent endothelial and smooth muscle cell cultures. Angiotensin II-induced migration of endothelial and smooth muscle cells was accompanied by tenascin deposition within extracellular matrix migration trails. Tenascin may function both as a defense against monocyte invasion and medial smooth muscle replication, as well as a substratum for directed endothelial and smooth muscle cell migration.

Stretch affects phenotype and proliferation of vascular smooth muscle cells

The exertion of periodic dynamic strain on the arterial wall is hypothesized to be relevant to smooth muscle cell morphology and function. This study has investigated the effect of cyclic mechanical stretching on rabbit aortic smooth muscle cell proliferation and expression of contractile phenotype protein markers. Cells were cultured on flexible-bottomed dishes and cyclic stretch was applied (frequency 30 cycles/min, 15% elongation) using a Flexercell Strain unit. Cyclic stretch potentiated smooth muscle cell proliferation in serum-activated cultures but not in cultures maintained in 0.5% fetal calf serum. Stretching induced a serum-independent increase of h-caldesmon expression and this effect was reversible following termination of mechanical stimulation. Strain was without effect on smooth muscle myosin or calponin expression. In cells grown on laminin stretch-induced h-caldesmon expression was more prominent than in cells cultured on collagen types I and IV, poly-L-lysine and gelatin. These data suggest that cyclic mechanical stimulation possesses dual effect on vascular smooth muscle cell phenotype characteristics since it: 1) potentiates proliferation, an attribute of a dedifferentiated phenotype; and 2) increases expression of h-caldesmon considered a marker of a differentiated smooth muscle cell state.

Representation of clinical problem assessment phrases in U.S. family practice using Read version 3.1 terms: a preliminary study

The Read Codes from the United Kingdom are a comprehensive clinical vocabulary, and one of the most likely candidates for adoption as a standard for use in Computer-Based Patient Record (CPR) systems. The new version 3.1 codes represent a major enhancement to the content and structure of the coding system, including incorporation of a new hierarchy and an explicit model for the use of qualifier terms. This is a preliminary study investigating the suitability of these codes for representing clinical problem assessment phrases in U.S. family practice. Problem assessment phrases from outpatient progress notes were encoded into the equivalent Read terms. The problem assessment phrases were evaluated for complexity and clarity. The coded representations of the phrases were evaluated for clinical acceptability. A list of coding difficulties was compiled. The most common difficulties were (1) qualifier terms present but not allowable for that Read concept (24%), and (2) qualifier terms not present (20%). British spelling and abbreviation variants were noted, but were relatively insignificant. The Read codes appear to be suitable for use in U.S. primary care practice with fairly minor modifications, but further development is required to expand the content and structure of the model for qualifier terms.

Activation of human peripheral monocytes by angiotensin II

This study has investigated the ability of the vasoconstrictor peptide angiotensin II to activate human peripheral blood monocytes. Activation was monitored by measuring both the release of tumor necrosis factor alpha from monocytes and their adhesion to monolayers of human endothelial cells. Angiotensin II-elicited activation of monocytes was dose-dependent (half-maximally effective concentration approximately 0.2 nM), saturable (maximally effective concentration approximately 5 nM), and sensitive to inhibition by the angiotensin type 1 receptor antagonist ZD 7155. Such direct actions imply that angiotensin II is an important candidate stimulus for the subendothelial infiltration of monocytes observed in atherogenesis and hypertension.

Characterization of angiotensin II receptors in cultured adult rat cardiac fibroblasts. Coupling to signaling systems and gene expression

Cardiac hypertrophy is largely due to cardiac fibroblast growth and increased synthesis of extracellular matrix. This study has investigated the contribution of the vasoactive hormone, angiotensin II, toward this hypertrophic process. We have demonstrated that cultures of adult rat cardiac fibroblasts express AT1 but not AT2 receptors for angiotensin II. The ability of angiotensin II to stimulate phosphoinositide catabolism and to elevate intracellular calcium concentrations in these cells was blocked by losartan, a specific AT1 receptor antagonist, but not by the AT2 receptor antagonist CGP 42112. Exposure of adult cardiac fibroblasts to angiotensin II resulted in the induction of several growth-related metabolic events including c-fos protooncogene expression and increased synthesis of DNA, RNA, and protein. Angiotensin II was also found to induce collagen type I, alpha 1 chain transcript expression in cardiac fibroblasts as well as the synthesis and secretion of collagen by these cells. The data demonstrate that angiotensin II, via AT1 receptors, can stimulate cardiac fibroblast growth and increase collagen synthesis in cardiac tissue. Thus, angiotensin II may contribute toward the development of cardiac hypertrophy in conditions of hypertension that are associated with elevated concentrations of angiotensin II.

Angiotensin-II-induced expression of laminin complex and laminin A-chain-related transcripts in vascular smooth muscle cells

Laminin, a major structural glycoprotein complex of basement membranes has been found to be modulated by angiotensin II in vitro and in vivo. In cultures of aortic organoids and vascular smooth muscle cells, expression of laminin was stimulated by exogenous vasoconstrictor peptide. Stimulation of laminin protein and mRNA expression was observed for both laminin B1/B2-chains and an unknown laminin heavy chain. Compared with PYS-2 cells, a mouse teratocarcinoma cell line which constitutively expresses a 10-kb mRNA transcript for 'classical' laminin A-chain, cultured vascular smooth muscle cells (VSMC) did not express a corresponding mRNA. However, cultured VSMC were found to express laminin A-chain-related mRNAs of approximately 1.8 kb and approximately 3.8 kb, respectively. The 1.8-kb species of transcript was expressed in a constitutive manner, whereas the 3.8-kb mRNA was found to be regulated by angiotensin II. Laminin complexes secreted by cultured cells contained a approximately 300 kD heavy chain which did not immunoreact with immunoreagents raised against either the classical laminin complex secreted by EHS tumor cells or the merosin heavy chain. The putative A-chain analogue possibly represents a new form of a tissue-specific laminin heavy chain, distinct from the A- and M-chains thus far described. Translation products encoded by the A-chain-related transcripts of cultured smooth muscle cells could not be specified using currently available antibodies. The putative protein(s) is speculated to contain the biological features of the N-terminus of the laminin A-chain, namely self-assembly and association with collagen type IV.

A comparison of nonthreaded, enhanced threaded, and Ellis fixation pins used in type I external skeletal fixators in dogs

Three different pin types (Ellis, enhanced threaded, and nonthreaded) were used in type 1 external skeletal fixation after transverse osteotomy of the radius and ulna in 12 skeletally mature dogs. Dogs were placed into three groups of four dogs based on the pin type used. Axial extraction forces were determined for each of the pin types after 8 weeks of weight bearing (chronic study). Nine contralateral radii were used to determine axial extraction forces for nine of each pin type not subjected to weight bearing forces (acute study). The force required for extraction of the enhanced threaded and Ellis pins in the chronic and acute studies was not significantly different. The force required to extract the nonthreaded pins was significantly less than that required for the other two pin types. Ground reaction forces had returned to levels measured before surgery by 2 weeks after surgery in the enhanced threaded and Ellis pin groups, however, dogs in the nonthreaded pin group required 4 weeks until normal ground reaction forces were measured. Radiographic evaluations 1, 2, 4, 6, and 8 weeks after surgery showed no difference among groups in the number of pin tract radiolucencies, however, the enhanced threaded pins had caused more trans-cortical chip fractures than the other two pin types. None of the pins broke during the eight-week chronic study.

Computerized medical records--new opportunities

The new generation of computer hardware and software is providing many new opportunities for physicians to use computerized medical records in their practices. A substantial number of new commercial systems have been introduced within the past few years, and many more will likely become available soon. In addition, there are opportunities for physicians to create their own customized systems using new software tools now available.

Concerted effects of lipoproteins and angiotensin II on signal transduction processes in vascular smooth muscle cells

Low-density (LDL) and high-density (HDL3) lipoproteins dose-dependently activate phosphoinositide turnover and elevate cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured vascular smooth muscle cells (VSMCs) from either human (microarterioles and aorta) or rat (aorta) sources. High-performance liquid chromatography analysis of cell extracts revealed comparable spectra of inositol phosphate isomers generated in response to either LDL, HDL3, or angiotensin II (Ang II). Thus, lipoproteins and Ang II may use similar, if not identical, signal transduction pathways for the generation and metabolism of inositol phosphates and intracellular Ca2+ mobilization in VSMCs. When Ang II was added in combination with either LDL or HDL3, the phosphoinositide and [Ca2+]i responses of VSMCs were either equal to or even greater than the sum of the effects elicited by the agonists individually. This additivity/synergy between Ang II and the lipoproteins was not accompanied by alteration in the half-maximally effective dose requirements of VSMCs for either Ang II (approximately 2 nmol/L, with or without lipoproteins) or lipoproteins (approximately 50 micrograms/mL for LDL and HDL3, with or without Ang II). Neither short-term (up to 10 minutes) nor long-term (48 hours) exposure of VSMCs to lipoproteins caused desensitization of phospholipase C and intracellular Ca2+ mobilization responses to either Ang II or lipoproteins. Since constant exposure of VSMCs to lipoproteins is a physiological circumstance, and because elevation of [Ca2+]i and activation of phosphoinositide turnover are pivotal events for VSMC contraction and growth, we suggest that the low concentrations of lipoproteins in the vessel intima may play an important role in regulating the response of the vasculature to Ang II.

Morphogenic effects of endothelin-1 on vascular smooth muscle cells

Endothelin-1 (ET-1), a vasoconstrictor peptide produced by endothelial and vascular smooth muscle cells (VSMC) might play a role in vascular remodelling. To investigate the proposed 'mitogenic' potential of ET-1, we examined the effects of chronic exposure of VSMC to ET-1 on cell cycle, growth/proliferation and differentiation under essentially mitogen-free culture conditions. Bulk cultures of thoracic aortic VSMC of spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats, although exhibiting genetically determined differences in growth/proliferation (due to shortened G1 and G2 phases in SHR VSMC), respond in a similar manner to ET-1 exposure: long-term exposure (12-15 days) of VSMC from both sources to ET-1 in nonmitogenic medium did not promote cycling of cells. On the contrary, ET-1 attenuated the cycling of VSMC which had already cycled beyond the S phase. For cells which had not cycled beyond the S phase, ET-1 interrupted progression through the cell cycle at the late G1/early S phase. The specific ability of SHR VSMC to grow in mitogen-free medium was abolished by ET-1, most likely via down-regulation of platelet-derived growth factor (PDGF)-alpha receptors. Subsequent to ET-1 exposure, VSMC expressed increased levels of mRNA and protein for smooth-muscle-specific alpha-actin. However, expression of smooth muscle alpha-actin did not predominate over beta-actin as observed for adult contractile VSMC in vivo. The ET-1-induced expression of smooth-muscle-specific alpha-actin mRNA was dose dependent (EC50 approx. 2 x 10(-9) M), and alpha-actin protein expressed was associated with organized actin fibers.

Identification of a fourth angiotensin AT1 receptor subtype in rat

Angiotensin II is a major regulator of cardiovascular function, fluid homeostasis and also plays a role in long-term cardiovascular disease processes. At present it is unclear if and how the diverse functions of angiotensin II may relate to different cellular receptors for this vasoactive peptide. In order to identify subtypes of angiotensin receptors we used a PCR-mediated cloning approach. Oligonucleotide sequences for PCR amplification of angiotensin receptors were selected on the basis of nucleotide sequences conserved between species. Since the coding regions of AT1-type receptors appear to be located on a single exon, we used genomic DNA as a template in the PCR reactions. Resulting amplification products represented a mixture of four different sequences as assessed by T-tracking and sequencing of the partial clones. Three of the clones encode for sequences already known, whereas the fourth clone encoded a novel receptor subtype which we have termed AT1C. Deduced amino acid sequences of the four different receptor subtypes are highly homologous. The AT1C receptor nucleotide sequence homology was greatest to the described AT3 receptor (95%) and less so to the published AT1A (90%) and AT1B (82%) receptor subtypes. The variety and tissue- specific expression of AT1 receptor subtypes and coexpression of different receptor subtypes may account for the diverse tissue- specific actions of angiotensin.

Effects of peptide vasoconstrictors on vessel structure

The peptide vasoconstrictors angiotensin II and endothelin-1, originally described as being derived exclusively from the plasma renin-angiotensin system and vascular endothelium, respectively, have been demonstrated to be produced independently of these sources. Local tissue angiotensin-generating systems are well documented and endothelin production has been demonstrated for a variety of nonendothelial cells, including vascular smooth muscle cells. There is increasing evidence that these locally produced vasoconstrictor peptides may contribute to blood vessel homeostasis, as well as the development of vascular pathologic conditions. Results obtained from pharmaceutical intervention in humans and animals of these systems strongly support this hypothesis. In addition to their vasoconstrictor properties, angiotensin II and endothelin-1 act as potent biologic effectors. In vitro, both vasoconstrictor peptides appear to modulate the activity of autocrine feedback loops in vascular smooth muscle cells. The activity of these feedback loops in vivo may represent a central mechanism for regulation and phenotypic differentiation of this cell type. The most well-established autocrine feedback loops of vascular smooth muscle cells are constituted by platelet-derived growth factor and transforming growth factor-beta, both of which are influenced by the action of angiotensin II and endothelin-1. The effects of the peptide vasoconstrictors on the (auto-) regulated feedback loops are of long-term structural importance, since both vasoconstrictors (via autocrine growth modulators) may influence the composition of the extracellular matrix of vascular smooth muscle cells. This includes effects on the synthesis and secretion of thrombospondin, fibronectin, tenascin, etc. The secretion of extracellular matrix glycoproteins themselves and incorporation into extracellular matrix in vitro appear to be linked to the activity of the autocrine feedback loops: e.g., stimulation of thrombospondin mRNA results in secretion of the glycoprotein only in the concomitant presence of exogenous platelet-derived growth factor, whereas the expression of fibronectin and tenascin may be directed by transforming growth factor-beta. The influence of angiotensin II and endothelin-1 on vascular smooth muscle cell surface receptor expression may represent a secondary mode of action of these vasoconstrictor peptides. Endothelin-1, for instance, can rapidly down-regulate platelet-derived growth factor-alpha receptor mRNA and both angiotensin II and endothelin-1, via induction of transforming growth factor-beta, may interrupt the platelet-derived growth factor based autocrine feedback loop. In vivo, the highly complex interactions between local and systemic vasoconstrictor production, autoregulated feedback loops, and extracellular matrix (which also serves as a reservoir for growth and differentiation modulators) are central to vessel homeostasis.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of soluble and insoluble fibronectin in rat aorta: effects of angiotensin II and endothelin-1

This study has investigated the influence of the vasoconstrictor peptides angiotensin II (Ang II) and endothelin-1 (ET-1) on fibronectin expression by vascular smooth muscle cells (VSMC). In confluent, quiescent cultures of VSMC, Ang II and ET-1 elevated fibronectin mRNA levels in a time- and dose-dependent fashion. ET-1 and Ang II also induced a time-dependent expression of immunoreactive fibronectin in cultures of aortic organoids, and for both peptides the fibronectin immunoreactivity was most prominent within those medial smooth muscle cell layers close to the vessel lumen. Immunoprecipitation of biosynthetically labelled fibronectin elaborated by cultured VSMC revealed a predominant expression of soluble fibronectin in response to Ang II, whereas for ET-1 the newly synthesized fibronectin was predominantly incorporated into the extracellular matrix deposit of the cells. These findings indicate that Ang II and ET-1 may exert disparate effects on smooth muscle cell phenotype and migration.

The renin-angiotensin system and extracellular matrix

A hallmark of vascular disease is the inappropriate proliferative and synthetic behaviour of vascular smooth muscle cells. This phenotypically immature behaviour arises as a consequence of the myocytes undergoing phenotypic conversion and/or clonal proliferation of a "fetal" type of smooth muscle cell preexisting in the vessel wall. De-differentiation and initiation of proliferation is not only induced by endothelial desquamation and acute exposure of smooth muscle cells to platelet-derived mitogens, but also occurs in the uninjured blood vessel. Therefore normal components of the blood vessel are implicit in the pathological process. These include vasoconstrictor peptides, growth factor peptides and extracellular matrix molecules. In vitro and in vivo experimentation has indicated that while some of these compounds individually are only mild stimulators of smooth muscle proliferative metabolism, they may act synergistically to induce robust responses. Here we discuss the effects of the vasoconstrictor peptide angiotensin II, which can be locally generated within the vessel wall itself, on the expression of extracellular matrix molecules in vitro and in vivo. We focus on the angiotensin II-modulated expression of extracellular matrix glycoproteins, e.g. thrombospondin, tenascin, fibronectin and laminin.