Elastin Composition Research Articles

Acellular vascular grafts generated from collagen and elastin analogs

Tissue-engineered vascular grafts require long fabrication times, in part due to the requirement of cells from a variety of cell sources to produce a robust, load-bearing extracellular matrix. Herein, we propose a design strategy for the fabrication of tubular conduits comprising collagen fiber networks and elastin-like protein polymers to mimic native tissue structure and function. Dense fibrillar collagen networks exhibited an ultimate tensile strength (UTS) of 0.71±0.06MPa, strain to failure of 37.1±2.2% and Young’s modulus of 2.09±0.42MPa, comparing favorably to a UTS and a Young’s modulus for native blood vessels of 1.4–11.1MPa and 1.5±0.3MPa, respectively. Resilience, a measure of recovered energy during unloading of matrices, demonstrated that 58.9±4.4% of the energy was recovered during loading–unloading cycles. Rapid fabrication of multilayer tubular conduits with maintenance of native collagen ultrastructure was achieved with internal diameters ranging between 1 and 4mm. Compliance and burst pressures exceeded 2.7±0.3%/100mmHg and 830±131mmHg, respectively, with a significant reduction in observed platelet adherence as compared to expanded polytetrafluoroethylene (ePTFE; 6.8±0.05×105 vs. 62±0.05×105 platelets mm–2, p<0.01). Using a rat aortic interposition model, early in vivo responses were evaluated at 2weeks via Doppler ultrasound and CT angiography with immunohistochemistry confirming a limited early inflammatory response (n=8). Engineered collagen–elastin composites represent a promising strategy for fabricating synthetic tissues with defined extracellular matrix content, composition and architecture.

Passive Pressure–Diameter Relationship and Structural Composition of Rat Mesenteric Lymphangions

Lymph flow depends on both the rate of lymph production by tissues and the extent of passive and active pumping. Here we aim to characterize the passive mechanical properties of a lymphangion in both mid-lymphangion and valve segments to assess regional differences along a lymphangion, as well as evaluating its structural composition. Mesenteric lymphatic vessels were isolated and cannulated in a microchamber for pressure-diameter (P-D) testing. Vessels were inflated from 0 to 20 cmH(2)O at a rate of 4 cmH(2)O/min, and vessel diameter was continuously tracked, using an inverted microscope, video camera, and custom LabVIEW program, at both mid-lymphangion and valve segments. Isolated lymphatic vessels were also pressure-fixed at 2 and 7 cmH(2)O and imaged using a nonlinear optical microscope (NLOM) to obtain collagen and elastin structural information. We observed a highly nonlinear P-D response at low pressures (3-5 cmH(2)O), which was modeled using a three-parameter constitutive equation. No significant difference in the passive P-D response was observed between mid-lymphangion and valve regions. NLOM imaging revealed an inner elastin layer and outer collagen layer at all locations. Lymphatic valve leaflets were predominantly elastin with thick axially oriented collagen bands at the insertion points. We observed a highly nonlinear P-D response at low pressures (3-5 cmH(2)O) and developed the first constitutive equation to describe the passive P-D response for a lymphangion. The passive P-D response did not vary among regions, in agreement with the composition of elastin and collagen in the lymphatic wall.

The Effect of Intermittent Umbilical Cord Occlusion on Elastin Composition in the Ovine Fetus

This study aimed to determine the effect of varying degrees of intermittent umbilical cord occlusion (UCO) on arterial elastin composition. Over 4 days, chronically catheterized late gestation fetal sheep received 5 total UCO per day lasting 1 min/h (mild group: n = 6), 2 min/h (moderate group: n = 4), 3 min/h (severe group; n = 6); or no occlusion (control group: n = 7). Each group was evaluated for elastin content of the carotid and superior mesenteric artery (SMA), the arterial pressure response to UCO, and plasma cortisol concentration. Elastin content of the carotid artery was significantly increased by severe UCO (9.5 µg/mg versus 6.4 µg/mg; P < .05) and insignificantly increased in mild and moderate groups, whereas UCO had no effect on elastin content of the SMA. This dose- and site-dependent response of the vasculature appears attributable to the hemodynamic changes that accompany UCO.

Fabrication of porous PCL/elastin composite scaffolds for tissue engineering applications

We present the development of a technique that enables the fabrication of three-dimensional (3D) porous poly(ɛ-caprolactone) (PCL)/elastin composites. High pressure CO 2 was used as a foaming agent to create large pores in a PCL matrix and impregnate elastin into the 3D structure of the scaffold. The effects of process variables such as temperature, pressure, processing time, depressurization rate, and salt concentration on the characteristics of PCL scaffolds were determined. Scaffolds with average pore sizes of 540 μm and porosity of 91% were produced using CO 2 at 65 bar, 70 °C, processing time of 1 h, depressurization rate of 15 bar/min, and addition of 30 wt% salt particles. The PCL/elastin composites were then prepared under different conditions: ambient pressure, vacuum, and high pressure CO 2. The fabrication of composites under vacuum resulted in the formation of nonhomogenous scaffolds. However, uniform 3D composites were formed when using high pressure CO 2 at 37 °C and 60 bar.

The effect of elastin on chondrocyte adhesion and proliferation on poly (ɛ-caprolactone)/elastin composites

The aim of this study was to demonstrate the effect of elastin on chondrocyte adhesion and proliferation within the structure of poly (ɛ-caprolactone) (PCL)/elastin composites. The homogenous 3D structure composites were constructed by using high pressure CO 2 in two stages. Porous PCL structures with average pore sizes of 540 ± 21 μm and a high degree of interconnectivity were produced using gas foaming/salt leaching. The PCL scaffolds were then impregnated with elastin and cross-linked with glutaraldehyde (GA) under high pressure CO 2. The effects of elastin and cross-linker concentrations on the characteristics of composites were investigated. Increasing the elastin concentration from 25 mg/ml to 100 mg/ml elevated the amount of cross-linked elastin inside the macropores of PCL. Fourier transform infrared (FTIR) analysis showed that elastin was homogeneously distributed throughout the 3D structure of all composites. The weight gain of composites increased 2-fold from 15.8 ± 0.3 to 38.3 ± 0.7 (w/w) % by increasing the elastin concentration from 25 mg/ml to 50 mg/ml and approached a plateau above this concentration. The presence of elastin within the pores of PCL improved the water uptake properties of PCL scaffolds; the water uptake ratio of PCL was enhanced 100-fold from 0.030 ± 0.005 g liquid/g polymer to 11.80 ± 0.01 g liquid/g polymer, when the elastin solution concentration was 50 mg/ml. These composites exhibited lower compressive modulus and energy loss compared to pure PCL scaffolds due to their higher water content and elasticity. In vitro studies show that these composites can support primary articular cartilage chondrocyte adhesion and proliferation within the 3D structures. These results demonstrate the potential of using PCL/elastin composites for cartilage repair.

Local mechanical and structural properties of healthy and diseased human ascending aorta tissue

This study investigates the mechanics and histology of healthy and dilated human ascending aortas (AA). The regional variation in mechanical response and tissue structure were compared. Rings of human AA from healthy (n=5), dilated tricuspid aortic valve (TAV, n=5), and dilated bicuspid aortic valve (BAV, n=6) patients were mechanically tested. Each aortic ring was sectioned into quadrants-anterior, posterior, medial (inner curvature) and lateral (outer curvature). Low- and high-stress elastic moduli were calculated from the equibiaxial stress strain curve to determine the local mechanical properties. Histological analysis was used to quantify the percent composition of elastin, collagen, and smooth muscle cells. BAV tissue was thinnest and contained the largest percent composition of collagen. Both TAV and BAV tissue had significantly less elastin than healthy tissue. At low strain in the circumferential direction, TAV tissue was on average the least stiff. The elastic modulus was dependent on quadrant and tissue type but not direction (isotropic). Generally, the lateral quadrant tissue was the stiffest and the medial quadrant the least stiff. There were no apparent local variations in the tissue histology. Local variations in tissue thickness and mechanical properties were evident in all samples analyzed and may be linked to the type of aortic valve present.

Development of a reinforced porcine elastin composite vascular scaffold

Elastin, a principal structural component of native arteries, has distinct biological and mechanical advantages when used as a biomaterial; however, its low ultimate tensile strength has limited its use as an arterial conduit. We have developed a scaffold, consisting of a purified elastin tubular conduit strengthened with fibrin bonded layers of acellular small intestinal submucosa (aSIS) for potential use as a small diameter vascular graft. The addition of aSIS increased the ultimate tensile strength of the elastin conduits nine-fold. Burst pressures for the elastin composite vascular scaffold (1,396 +/- 309 mmHg) were significantly higher than pure elastin conduits (162 +/- 36 mmHg) and comparable to native saphenous veins. The average suture pullout strength of the elastin composite vascular scaffolds was 14.612 +/- 3.677 N, significantly higher than the pure elastin conduit (0.402 +/- 0.098 N), but comparable to native porcine carotid arteries (13.994 +/- 4.344 N). Cyclic circumferential strain testing indicated that the composite scaffolds were capable of withstanding physiological loading conditions for at least 83 h. Implantation of the elastin composites as carotid interposition grafts in swine demonstrated its superiority to clinically acceptable ePTFE with significantly longer average patency times of 5.23 h compared to 4.15 h. We have developed a biologically based elastin scaffold with suitable mechanical properties and low thrombogenicity for in vivo implantation, and with the potential for cellular repopulation and host integration reestablishing an appropriate elastic artery.

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Influence of regular exercise on age-related changes in arterial elasticity: mechanistic insights from wall compositions in rat aorta.

Arterial stiffness increases with age in healthy sedentary adults. We previously reported that the age-related increases in arterial stiffness are absent or attenuated in regularly exercising adults. However, the mechanism underlying this training effect is unknown. One possibility is that regular exercise minimizes age-related changes in the arterial wall composition of elastin and collagen. To gain insight into this issue, we studied four groups of rats (N = 23): young (42-46 wks) and old (80-84 wks), sedentary and exercise-trained. The exercise group swam 1 hr.d-1, 6 d.wk-1 for 17-21 weeks. There was no significant difference in the incremental elastic modulus between young sedentary and exercise-trained rats. The elastic moduli of the old exercise-trained rats were 31% lower than in the old sedentary controls. As such, the magnitude of age-related increase in the elastic modulus was smaller in the exercise-trained (110%) vs. the sedentary group (151%) (p < 0.05). In both activity groups, elastin content was lower and collagen content was higher in old vs. young rats (p < 0.05). However, there were no significant differences between the two activity groups. These results are not consistent with the hypothesis that regular physical exercise minimizes age-related compositional changes in the arterial wall and attenuates the age-related increase in arterial stiffness.

Physicochemical properties of arterial elastin and its associated glycoproteins

Microfibrillar glycoproteins are a significant component of vascular elastic tissue, but little is known about their contribution to vascular physiology and pathology. We have investigated some physicochemical properties of the glycoproteins that may be pertinent to these roles. Because of the difficulty in isolating intact glycoproteins in a form and quantity suitable for physicochemical examination, we based our analysis on a comparison of the properties of porcine thoracic aorta and pulmonary artery extracted with GuHCl and collagenase (preparation GC) and after further treatment with dithioerythritol to remove glycoproteins (preparation GC/DTE). Amino acid analysis showed that GC/DTE had the amino acid composition of pure elastin while GC contained a higher proportion of polar amino acids, particularly in the aortic preparation. GC stained with alcian blue, particularly in the intimal region, but GC/DTE did not. GC had a higher water content and a slower viscoelastic response and the circumferential elastic modulus was approximately 50% lower (whether expressed in terms of sample weight or elastin content). Clearly, therefore, the microfibrils do not stiffen the network and may prevent the alignment of elastin fibers in the circumferential direction. Their effect on hydration may arise either because they impose mechanical constraints on the geometry of the network or because they modify the inter- and intramolecular hydrophobic or electrostatic interactions that influence the tissue organization and hydration. Molecular probe measurements of the intrafibrillar pore structure using radiolabeled and fluorescent probes showed that removal of the microfibrils caused a slight decrease in the extrafibrillar water space and a larger decrease in the intrafibrillar water space. Sucrose, a small probe molecule, was able to penetrate most of the intrafibrillar water space when microfibrils were present but was virtually excluded when they were not. Potentiometric titration and radiotracer assays of ion binding both showed that the microfibrils contribute a considerable negative charge (−9 μmoles/g wet tissue in the aortic preparation and −16 μmoles/g wet weight in the pulmonary artery) and increase calcium binding by approximately 30%. © 1999 John Wiley & Sons, Inc. Biopoly 49: 255–265, 1999

Physicochemical properties of arterial elastin and its associated glycoproteins.

Microfibrillar glycoproteins are a significant component of vascular elastic tissue, but little is known about their contribution to vascular physiology and pathology. We have investigated some physicochemical properties of the glycoproteins that may be pertinent to these roles. Because of the difficulty in isolating intact glycoproteins in a form and quantity suitable for physicochemical examination, we based our analysis on a comparison of the properties of porcine thoracic aorta and pulmonary artery extracted with GuHCl and collagenase (preparation GC) and after further treatment with dithioerythritol to remove glycoproteins (preparation GC/DTE). Amino acid analysis showed that GC/DTE had the amino acid composition of pure elastin while GC contained a higher proportion of polar amino acids, particularly in the aortic preparation. GC stained with alcian blue, particularly in the intimal region, but GC/DTE did not. GC had a higher water content and a slower viscoelastic response and the circumferential elastic modulus was approximately 50% lower (whether expressed in terms of sample weight or elastin content). Clearly, therefore, the microfibrils do not stiffen the network and may prevent the alignment of elastin fibers in the circumferential direction. Their effect on hydration may arise either because they impose mechanical constraints on the geometry of the network or because they modify the inter- and intramolecular hydrophobic or electrostatic interactions that influence the tissue organization and hydration. Molecular probe measurements of the intrafibrillar pore structure using radiolabeled and fluorescent probes showed that removal of the microfibrils caused a slight decrease in the extrafibrillar water space and a larger decrease in the intrafibrillar water space. Sucrose, a small probe molecule, was able to penetrate most of the intrafibrillar water space when microfibrils were present but was virtually excluded when they were not. Potentiometric titration and radiotracer assays of ion binding both showed that the microfibrils contribute a considerable negative charge (-9 mumoles/g wet tissue in the aortic preparation and -16 mumoles/g wet weight in the pulmonary artery) and increase calcium binding by approximately 30%.

Hypertrophy of colonic smooth muscle: structural remodeling, chemical composition, and force output.

The cellular basis of adaptations occurring during the development of megacolon was studied with the lethal spotted mouse model. Age-dependent changes in the length-force characteristics of the colon reach a steady state by 3-4 mo and include an increased relative force development at very short muscle lengths. In megacolon the following occur: 1) structural remodeling expressed as a greater increase in the fraction of maximum force production at short lengths, a shift of optimum length (Lo) to longer lengths, and no change in force per square centimeter; 2) hypertrophy and hyperplasia of both circular and longitudinal muscle; 3) high resting compliance consistent with no disproportionate change in collagen or elastin composition; 4) marked distension so that in situ circumference approximately 1.8 Lo, where active force production is low, and 5) slack length approximately 0.65 Lo, as in normal colon. Biochemical remodeling in megacolon includes disproportionate increases in ATP and phosphocreatine concentration, with 3.5-fold more preformed phosphagen than in normal colon. The myosin concentration is the same in both muscles, but the actin concentration is 1.5-fold greater in megacolon. Most of the cellular changes in megacolon would facilitate high active force output from the muscle at much larger intestinal diameters.

The intermediate layer: A morphologic study of the elastin and hyaluronic acid constituents of normal human vocal folds

The lamina propria of vocal folds are important in voice production. We evaluated the morphologic features of elastin and hyaluronic acid, two important constituents of the lamina propria. Thirty normal human vocal folds were obtained from patients dying of traumatic causes without vocal fold injury. These tissues were immediately prepared for histologic and ultrastructural examination by standard methods. For specific study of the ultrastructure of the layers of the lamina propria, six vocal folds were divided horizontally through the midplane of the lamina propria. We found that the elastin composition of the vocal folds is variable, the largest amount being seen in the midportion on elastin-van Gieson (EVG) staining and ultrastructural evaluation. The superficial layer of the lamina propria contains fewer large elastin fibers. In this region, we found that elastin was predominantly composed of elaunin and oxytalan, which stain poorly with EVG. Using computer-assisted image analysis, we quantified the differences in elastin composition between the layers. The amount of elastin varied between men and women, and these differences could not be accurately measured by the methods employed. Hyaluronic acid was abundant especially in the midportion of the lamina propria and was significantly more abundant in men than women on quantification. The significance of these observations in normal vocal folds is discussed.

Changes in biomechanical properties, composition of collagen and elastin, and advanced glycation endproducts of the rat aorta in relation to age

During ageing and senescence the aorta becomes stiffer and its elasticity is reduced. The mechanism causing this increased stiffness of the aortic wall was studied using a rat model. Ring-shaped samples were prepared from the thoracic aorta of three groups of rats aged 4.5, 14 and 27 months, representing young, adult and old animals. Analysis of the static biomechanical properties showed increased diameter (2.20 ± 0.03 mm) and increased stiffness (4.0 ± 0.2 mN) of aortic samples from old rats compared with adult rats (1.82 ± 0.02 mm and 3.0 ± 0.1 mN, respectively). The total hydroxyproline and elastin content per sample was not changed. However, the hydroxyproline content/mm 2 of the aortic wall was reduced by 20% and the elastin content/mm 2 of the aortic wall was reduced by 19% comparing the old with the adult rats. No differences were found in the pyridinoline concentrations between old and adult rats. The collagen- and elastin-associated fluorescence was determined as a marker of advanced glycation endproducts (AGE). Both parameters were increased in the old rats compared with the adult rats, by 42% and 17%, respectively, and positively correlated with stiffness at physiological loads. A positive correlation between collagen-associated fluorescence and maximum stiffness was found as well. In conclusion, the age-related increase in stiffness of the aorta was associated with increased diameter, reduced collagen and elastin contents/mm 2 of the aortic wall, increased fenestration of elastic laminae and accumulation of fluorescent material in collagen and elastin.

Perinatal hypocuprosis affects synthesis and composition of neonatal lung collagen, elastin, and surfactant

To investigate the role of iron, ascorbate, and fructose on copper depletion and the effect of copper depletion on neonatal lung collagen, elastin, and surfactant, female rabbits were fed a control diet [10 parts per million (ppm) copper], a basal marginal copper diet (1.5 ppm), or a basal diet containing a high concentration of iron (1,750 ppm), ascorbic acid (1%, wt/wt), or fructose (20% of carbohydrates, wt/wt) or a combination of iron, ascorbic acid, and fructose throughout gestation. Whereas 10% of neonates in the control group died in the first 24 h, 27-67% of the offspring of rabbits fed the marginal copper diet died. Birth weight was also lower for the pups of the females fed the marginal copper diets. Lungs of neonates born to females fed iron or ascorbate and marginal copper diets had low levels of copper, high proportions of acid-extractable, high-molecular-weight collagen, and low lysyl-oxidase activities, consistent with incomplete maturation of collagen. The bronchoalveolar lavage fluids of newborns whose mothers were fed marginal copper diets alone or in combination with iron and/or ascorbate had lower levels of total surfactant phospholipids than the fluids from lungs of control newborns. The lower surfactant phospholipid content of these groups could be attributed mainly to lower phosphatidylcholine and, in particular, dipalmitoylphosphatidylcholine levels. These results suggest that high maternal intakes of iron, ascorbate, or their combination in pregnancy deplete biologically available copper, which in turn induces neonatal lung abnormalities.

Use of Arterial Compliance for Evaluation of Hypertension

Arterial compliance describes a change in the volume of arteries following a change in blood pressure. The physical basis of the compliance concept and experimental procedures in animals both indicate that the relation between arterial compliance and blood pressure pattern is often unclear. Compliance is pressure-dependent because of the biphasic elastin and collagen composition of arteries and, hence, decreases when blood pressure increases. Compliance also determines the pulsatile amplitude of the pressure wave by regulating the buffering function of an artery's face to the cardiac pump and, accordingly, its reduction induces a selective increase in systolic level. The questions are whether these theoretical and experimental phenomena can be extrapolated to human hypertension and whether they can be assessed from indirect measurement of arterial compliance by means of a time-domain analysis of arterial pressure and flow waves via various models of the arterial tree. Whatever the method and site of measurement, arterial compliance was found to be decreased in different forms of hypertension. This low compliance can be considered to have a causal role in elderly patients with isolated systolic hypertension. In contrast, in patients with systolo-diastolic hypertension physiologic and pharmacologic arguments exist against the fact that low arterial compliance may be the pure consequence of mean blood pressure elevation. Moreover, it is suggested that aging acts in concurrence with pressure elevation to decrease arterial compliance, and that in certain hypertensive patients additional factors, perhaps atherosclerotic in nature, contribute to impair the elastic properties of arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in the elastic tissue of the human thoracic aorta

Thirty human aortas with varying degrees of atheroma graded macroscopically according to the WHO classification were taken at autopsy from subjects of different ages (24–86 years). Study by light microscopy showed aortas with an intact wall (4 subjects, 25–46 years) with a thin intima and regular elastic layers, and aortas with varying degrees of modification of the wall, where the intima was of varying thickness and the elastic fibers showed varying degrees of damage (moderate lesions: 5 subjects, 35–52 yrs; severe lesions: 21 subjects, 26–86 yrs). From each aorta, a 4-cm segment from the tunica media, free of atheromatous lesions, was defatted and subjected to successive treatment with EDTA-Tris, 6 M guanidine-HCl-Tris, 6 M guanidine-HCl-Tris-DTE and collagenase. The residues (EP residues) were subjected to amino acid (AA) analysis and transmission electron microscopy (TEM) study. In the young subject, the AA composition was similar to that of elastin and the TEM images were characteristic of this substance. In the aging subject, an increase in polar AA and a parallel decrease in apolar AA and crosslinks was noted. By TEM, the elastin was seen to be associated with abundant fibrillar material. Trypsin treatment of EP residues gave E residues, whose composition and TEM appearance were similar in all samples, corresponding to the standard composition of elastin and its classic appearance by electron microscopy. We suggest that the fibrillar material removed by trypsin is the morphological reflection of the chemical variations observed in the EP residues. These correspond to contamination of the elastin by a polar protein fraction. This contamination is closely correlated with age but not with the degree of atheroma. Thus the age-related chemical changes in elastin appear to be independent of the onset and evolution of atheromatous lesions. The 10–15 nm diameter of the contaminating fibrillar material suggests this may be the microfibrillar fraction of elastic tissue.

Elastin in the human intervertebral disk

The elastic fiber and elastin in the human yellow ligament and intervertebral disk were studied histologically and biochemically. The elastic fiber in the human intervertebral disk, which until now had not been clearly identified microscopically, was observed clearly. We found the distribution of the elastic fiber in the intervertebral disk to be very sparse and irregular, and its diameter was small, being about one-tenth of that found in the yellow ligament. The elastin contents of the yellow ligament and intervertebral disk were 46.7% +/- 0.9% and 1.7% +/- 0.2% respectively (mean +/- SE) of the total dry weight. The amino acid composition of elastin in the yellow ligament is similar to that of other tissue, as reported in the literature; however, that found in the intervertebral disk is significantly different. It would appear, therefore, that the elastin in the intervertebral disk is of a different type from that found elsewhere.

Aging effects on the elastin composition in the extracellular matrix of cultured rat aortic smooth muscle cells.

Elastin accumulation in the extracellular matrix of cultured rat aortic smooth muscle cells was monitored as a function of age. The effect of the animal donor age and time in culture in single or consecutive passages on the cells' ability to accumulate total protein as well as elastin was evaluated. Smooth muscle cells were obtained from animals ranging in age from 2 d to 36 mo. Protein accumulation by the cells based on DNA content was similar regardless of which of the above aging parameters was examined. Although there were significant amounts of elastin present in the extracellular matrix of those cells originating from the younger animals (2 d and 6 wk old), little or none was detected in cell cultures derived from the oldest animals. A soluble elastin-like fraction which was isolated from the cultures of the 2-d-old rats seemed to be lacking in the cultures of cells from the 36-mo-old animals. This observation may, in part, explain the absence of insoluble elastin in the matrix of some cultures obtained from older animals. The data strongly suggest that the age of the donor animal from which the cells originate has the greatest influence on in vitro elastin accumulation.

Changes in elastin composition in aorta of spontaneously hypertensive rats (SHR)

Tropoelastin and elastin preparations obtained from aortae of spontaneously hypertensive rats (SHR) show an increased proportion of polar amino acids (aspartic acid, glutamic acid, arginine and tyrosine). The content of these amino acids is 1.43–3.04 times higher in SHR rats than in similar elastin or tropoelastin preparations obtained from normotensive animals. On the other hand elastin and tropoelastin preparations obtained from SHR rats show a lower frequency of the Val-Pro sequence; this was found to be 35.93 per 1000 amino acid residues in SHR rats as compared to 51.04 per 1000 amino acids in the preparations obtained from control animals. Since similar differences were found not only in elastin preparations but also in tropoelastin, contamination of these preparations with an acidic protein seems unlikely. In general the results obtained are similar to those seen in animals kept on a long term high fat diet. It appears feasible to suggest that these differences are caused by a changed proportion of two different elastin type.