Lamellar Units Research Articles

Aortic Compliance in Hypercholesterolemic Watanabe Rabbits Compared to Normal New Zealand Controls

This study was designed to test the hypothesis that severe atherosclerosis changes aortic compliance. Compliance of a vessel is defined as change in volume per unit change in pressure and is a measure of the stiffness or distensibility of the vascular wall. Part of the energy delivered by the left ventricle in systole is used to propel the blood forward into the aorta and part of it to distend the aorta and major vessels. During diastole, the arterial walls recoil and provide energy for propulsion of blood, thereby making blood flow continuous. It is known that Watanabe hereditary hyperlipidemic rabbits develop severe atherosclerosis beginning at 6 months of age. Compliance of the ascending thoracic aorta was studied angiographically in eight Watanabe hereditary hyperlipidemic rabbits of ages greater than 6 months and six normal lipidemic New Zealand white rabbits of ages greater than 6 months, used as controls. The normal New Zealand white rabbits had an average blood cholesterol of 27.4 mg/dL, SD = 13.8, and a regional compliance in the ascending aorta of 0.004 mL/mm Hg, SD = 0.002, compared to the Watanabe hereditary hyperlipidemic rabbits with a cholesterol of 583.1 mg/dL, SD = 162.7, and a compliance of 0.0022 mL/mm Hg, SD = 0.0015. These are significant differences (p less than .05). In addition, the histopathology of the aorta of the Watanabe hyperlipidemic rabbit compared to that of the controls showed a significant decrease in the number of medial lamellar elastin units, an indicator of the decreased elasticity of the blood vessel wall.

Conducting pulmonary arteries: structural adaptation to extrauterine life in the pig.

A quantitative light microscopical and ultrastructural study of the elastic and large muscular pulmonary arteries of 30 Large White pigs aged from birth to 6 months yielded light microscopical measurements on 120 arteries and 62,560 ultrastructural assessments, which composed a computerised database. After birth mean arterial medial thickness and mean smooth muscle cell diameter decreased during the first 4 days (p less than 0.01). Mean interlamellar distance decreased, reaching its nadir at 1-3 weeks (p less than 0.01). All these features increased between 3 weeks and adulthood (p less than 0.01). In the smooth muscle cells synthetic rather than contractile organelles were dominant during the first 3 weeks. Between 3 weeks and adulthood, however, smooth muscle cell myofilament volume density increased (p less than 0.0001). At all ages the smooth muscle cells of the outer lamellar units of elastic arteries had a greater myofilament volume density than those of adluminal units (p less than 0.0001). The amount of connective tissue increased between 3 weeks and adulthood, collagen and basement membrane increasing preferentially (p less than 0.0001, p less than 0.05, respectively). Thus the conducting pulmonary arteries, like the peripheral resistance arteries, adapt structurally to extrauterine life. Remodelling occurred rapidly after birth, and then gradually during growth, as connective tissue was deposited and smooth muscle cells matured.

Role of medial lamellar architecture in the pathogenesis of aortic aneurysms

The human abdominal aorta is particularly susceptible to the formation of aneurysms with atrophic walls. This aortic segment normally has fewer medial lamellar units than would be expected for a mammalian aorta of comparable diameter as well as far fewer medial vasa vasorum than would be expected for an aortic wall of comparable thickness. To test the hypothesis that ischemia and/or loss of normal lamellar architecture are predisposing factors for aneurysm formation, we used the pig thoracic aorta, which is furnished with 75 medial layers and vasa supplying the outer two thirds. Vasal blood flow was surgically ablated, and crushing injury was used to reduce the number of intact lamellar units. Mural ischemia alone resulted in necrosis of cells in the medial zone furnished by vasa but did not lead to aneurysmal dilatation, and all the fibrous tissue layers persisted during the 2-month observation period. Mechanical injury resulted in aneurysms in both ischemic and nonischemic aortic segments, but only if fewer than 40 intact lamellae remained and the average tension per lamellar unit exceeded three times the normal value of 1316 ± 202 dynes/cm (4543 ± 1624 for ischemic and 4087 ± 871 for nonischemic segments; p < 0.01 for each). We conclude that a critical reduction in the number of intact lamellar units results in aneurysmal dilatation. Protracted medial ischemia due to intimal plaque formation in the avascular abdominal aorta may eventually reduce the number of intact lamellae and favor the development of aneurysms.

The effects of remodeling on the elastic properties of bone.

Cortical bone can be modeled as a complex hierarchical composite interrelating both structure and material properties on four levels of structural organization: molecular, ultrastructural, microscopic, and macroscopic. In young animals, the microstructural systems are long parallel lamellar units, plexiform bone, which in older or more mature animals converts by internal remodeling into multiple concentric lamellar units, secondary osteons, forming haversian bone. Ultrasonic wave propagation measurements performed on both plexiform and haversian bone clearly show a definitive relationship with microstructure; haversian bone can be described as a transversely symmetric material whereas plexiform bone appears to be orthotropic in nature. The anisotropy of the elastic constants are found to reflect the tissue symmetry; moreover, plexiform bone is stiffer and more rigid in all directions than is haversian bone. Similar experiments were performed on osteoporotic and osteopetrotic bone. While the results for osteoporotic bone are understandable in terms of the increased porosity, the results for the osteopetrotic bone are anomalous with respect to its density. Since Wolff, the remodeling of bone has been interpreted as a way of altering the mechanical properties to suit some need. For haversian remodeling from plexiform bone, the argument that adaptation occurs to optimize properties requires additional clarification since haversian bone appears to have inferior mechanical properties to plexiform bone.

Medial elastin in the thoracic and abdominal aorta of sheep and lambs.

Aortas were removed from six mature lambs and four sheep and pressure fixed at 100 and 120 mmHg pressure (1 mmHg = 133.322 Pa), respectively, in 10% buffered formalin. The numbers of elastin layers were counted from cross sections at different distances down the aorta, from the distal arch to the iliac bifurcation, and showed a linear decrease in the thoracic aorta. In the abdominal aorta there was no difference in values from the diaphragm to the aortoiliac bifurcation in the lamb, but a slight decrease in the sheep. If y = mx + b, where y is the number of medial lamellar units (MLU), b the intercept, x the distance from the last brachiocephalic branch in centimetres, and m the slope, we obtained the following equations (with standard deviations): lamb thoracic aorta; y = -6.29 (+/- 0.71)x + 106 (+/- 12); sheep thoracic aorta; y = -3.46 (+/- 0.40)x + 140 (+/- 21.4); lamb abdominal aorta; y = 0.51 (+/- 1.48)x + 37 (+/- 7.7); sheep abdominal aorta; y = -0.85 (+/- 0.28)x + 66 (+/- 5.9). Tension per lamellar unit was calculated and plotted versus distance yielding a linear increase in the entire lamb aorta but an abrupt increase between thoracic and abdominal aortas in the sheep. This causes the pulse wave to move uniformly with increasing speed along the length of the lamb aorta but would cause an abrupt change in the wave at or about the diaphragm in the sheep. Distortions in the pulse wave could produce local stress concentrations in the abdominal aorta which might render it more susceptible to atherosclerosis than the thoracic aorta.

The pattern of elastin in the aorta and large arteries of mammals.

The arteries of mammals contain large amounts of elastin arranged in concentric lamellae known as medial lamellar units (MLU). In adult mammals of a variety of species the number of lamellar units is roughly proportional to the radius of the artery and the tension/MLU ratio is roughly constant in all species, but greater in the abdominal than in the thoracic aorta. Re-analysis of these data shows that the number of MLU of the abdominal aorta is linearly related to the pulse pressure, while the number of MLU in both the thoracic and abdominal aorta increases exponentially with stroke volume. Preliminary data are presented showing the decrease in number of MLU along the thoracic aorta of both fetal lambs and sheep, and evidence is provided that some of this elastin may be involved in the formation of the small arteries, such as the intercostals, which arise from the aorta. Scanning electron microscopy showed that the elastin on the intimal side of the media was in the form of fenestrated sheets while that on the adventitial side was a fibrous network. The size and density of the fenestrations was greater in fetal lambs and may play a role in allowing growth of the artery.

Biochemical profiles of membranes from x-ray and neutron diffraction

X-ray and neutron diffraction methods provide some information about the distribution of mass in biological membranes and lipid-water systems. Scattering density profiles obtained from these systems, however, usually are not directly interpretable in terms of the relative amounts of chemical constituents (e.g., lipid, protein, and water) as a function of position in the membrane. We demonstrate here that the combined use of x-ray and neutron-scattering profiles, together with information on the total amounts of each of the major membrane components, are sufficient to calculate unambiguously the volume fractions of these components at well-defined regions of the lamellar unit. Three cases are considered: a calculated model membrane pair, dipalmitoylphosphatidylcholine-water multilayers, and rabbit sciatic nerve myelin. For the model system, we discuss the limitations imposed by finite resolution in the diffraction patterns. For the lipid-water multilayers, we calculate water volume fractions in the hydrocarbon tail, lipid headgroup, and interlamellar regions; estimates of these values by various methods are in good agreement with our results. For the nerve myelin, we predict new results for the distribution of protein through the membrane.

Histology of normal aortas in non-human primates with emphasis on diffuse intimal thickening (DIT)

Little information is available on the histology of the normal aorta in non-human primates, despite their extensive use in atherosclerosis research. This paper consists of a detailed histologic description of normal aortas from 28 non-human primates, including 20 species. Medial and adventitial coats were essentially normal in all animals, and the former were composed of lamellar units similar in structure to those described in detail by other investigators. Intimal thickenings were present in 24 of the 28 individuals. These thickenings were similar in morphology to those of diffuse intimal thickening (DIT) in humans and other animals, and were more prevalent in older animals and in larger animals. The thickenings were not more prevalent or more pronounced in any particular region of the aorta, and their distribution did not provide a clue as to their etiology. Findings suggested that the thickenings underwent recognizable stages of growth and maturation, and that growth was accomplished by the addition of smooth muscle cells at the intimomedial junction.

The cubic phase of monoglyceride-water systems. Arguments for a structure based upon lamellar bilayer units

A combination of low-angle X-ray diffraction and NMR diffusion techniques may be used for the elucidation of the internal structure of cubic lyotropic liquid crystalline lipid systems. The advantage of the NMR method for this kind of struc- ture determinations lies in the facts that restricted diffusion can be observed and that the lateral diffusion in lamellar systems can be measured directly. The value of the apparent diffusion coefficient depends strongly on the overall structural geometry. Previous X-ray diffraction findings for the cubic phase occurring in aqueous monoglyceride systems have been reevaluated and supplemented and arguments are presented for an internal structure built up of small lamellar bilayer units. The lamellar units are ideally hexagon-shaped disks connected in such a manner that they form a close-packed system of tetrakaidecahedra in which the quadrilateral faces are missing. Thus is obtained an open structure which is optically isotropic and is continuous in three axial directions both with respect to the nonpolar lipid and the polar aqueous regions. This structure concept of two con- tinuous regions where the lipid regions consist of a system of lamellar units obtains support from values for the translational diffusion coefficients of the lipid (and water) measured with the NMR pulsed magnetic field gradient method. This type of cubic phases, which occurs in many monoglyceride systems and which can be mixed with other lipids such as lecithin or choles- terol and also with proteins, may be used as model membrane systems.

A sequential ultrastructural study of different arteries in the hypertensive rat

Hypertensive vascular disease was induced in rats using weekly injections of deoxycorticosterone and substituting 1% sodium chloride for tap water to drink. The emphasis of the study was on the progression and comparative aspects of alterations produced in the large clastic vessels and the coronary artery. One of the carliest alterations was observed in the intima of all vascular segments. These were characterized by endothelial cell enlargement and a gradual subendothelial accumulation of granular material leading to intimal thickening. In the later stages of the disease, mononuclear cells, fibrin and smooth muscle cells were present within the intima, with the exception of the coronary artery; only smooth muscle cells were seen in the intimal portion of this vessel. Early changes in the media consisted of smooth muscle hypertrophy and widened lamellar units, resulting in increased thickness of the vessel wall. These alterations progressed to include variation in the shape of smooth muscle cells, increasing disorganization of the cellular arrangement, focal cytoplasmic necrosis, and the loss of entire smooth muscle cells. A definite regional difference in susceptibility of individual mural components to hypertensive damage was noted. The most striking feature of this difference was demonstrated by the relatively early, severe involvement of the media of the coronary artery, in contrast to the other arteries examined. These alterations may be initiated by increased intraluminal pressure. In the case of the coronary artery, failure of this vessel to adapt effectively to increased mural tension by structural re-modelling of the arterial wall, may exacerbate these alterations.

Folded bilayers — an alternative to the rippled lamellar lecithin structure

Evidence is given for the existence of a folded lamellar structure above the so-called pretransition before chain melting in lecithin-water systems. The structure consists of lamellar units with vertical chains alternating with lamellar units with tilted chains and it is an alternative to the rippled structure proposed for lamellar phase Pβ.

The structure of crystalline polyethylene sulphide ? a laser Raman study

That polyethylene sulphide crystallizes in lamellar units within spherulites, has been presumed. In this paper further evidence for lamellae from Raman spectroscopy is presented and discussed. Thickening of the lamellae betweenTM-90 andTM-15 is also demonstrated.

Carotid artery mechanics, connective tissue, and electrolyte changes in puppies.

ARTICLESCarotid artery mechanics, connective tissue, and electrolyte changes in puppiesRH Cox, AW Jones, and GM FischerRH Cox, AW Jones, and GM FischerPublished Online:01 Sep 1974https://doi.org/10.1152/ajplegacy.1974.227.3.563MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByAxial nonuniformity of geometric and mechanical properties of mouse aorta is increased during postnatal growthYi Huang, Xiaomei Guo, and Ghassan S. Kassab1 February 2006 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 290, No. 2Vascular AdaptationIn vivo and in vitro mechanical properties of the sheep thoracic aorta in the perinatal period and adulthoodSarah M. Wells, B. Lowell Langille, and S. Lee Adamson1 May 1998 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 274, No. 5Mechanical Properties and Active Remodeling of Blood VesselsMechanical Properties of Arteries and Arterial GraftsSelective determination of Triton-type non-ionic surfactants in different samples by on-line clean-up and FIAFresenius' Journal of Analytical Chemistry, Vol. 337, No. 4Organogenesis of the Arterial WallThe common carotid circulation in patients with essential hypertension.Stroke, Vol. 19, No. 10Age-Related Changes in Selected Animal SpeciesAortic Connective Tissue Content in White Leghorn FemalesPoultry Science, Vol. 65, No. 2Transmural organization of the arterial media. The lamellar unit revisited.Arteriosclerosis: An Official Journal of the American Heart Association, Inc., Vol. 5, No. 1Contractions in normal and atherosclerotic rabbit aortasMechanisms of Ageing and Development, Vol. 26, No. 2-3Force-Velocity Relationships of Guinea Pig UreterJournal of Urology, Vol. 131, No. 5Age-associated alterations in viscoelastic properties of canine aortic strips.Circulation Research, Vol. 53, No. 4Analysis of the passive mechanical properties of rat carotid arteriesJournal of Biomechanics, Vol. 16, No. 9Electrolyte Metabolism of the Arterial WallTHE EFFECT OF ALTERATIONS IN SCLEROPROTEIN CONTENT ON THE STATIC ELASTIC PROPERTIES OF THE ARTERIAL WALLModifications by stretches of the mechanical response of isolated cerebral and extracerebral arteries to vasoactive agentsPfl�gers Archiv European Journal of Physiology, Vol. 374, No. 1Arterial Smooth Muscle MechanicsLongitudinal force and stress of rat's esophagus: age-related changes.M P Zabinski, and P Biancani1 June 1977 | American Journal of Physiology-Endocrinology and Metabolism, Vol. 232, No. 6Interaction of Low Density Lipoproteins with Small and Large MoleculesEffects of spontaneous hypertension and age on arterial connective tissue in the ratExperimental Gerontology, Vol. 11, No. 5-6Altered arterial connective tissue in racing greyhound dogsExperientia, Vol. 31, No. 12Development of longitudina retraction of carotid arteries in neonatal dogsExperientia, Vol. 31, No. 11 More from this issue > Volume 227Issue 3September 1974Pages 563-568 Copyright & PermissionsCopyright © 1974 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1974.227.3.563PubMed4412337History Published online 1 September 1974 Published in print 1 September 1974 Metrics

The lamellar structure of nerve myelin after rehydration

New low-angle X-ray diffraction data have been obtained from nerve myelin after rehydration. The X-ray patterns show the first six orders of diffraction of a lamellar repeat unit of about 100 Å. Direct methods of structure analysis have been used to determine uniquely the phases of the first three orders of diffraction. The electron density profile of rehydrated nerve myelin has been obtained on an absolute electron density scale and is compared with the electron density profile of normal nerve myelin at the same resolution of 16–17 Å. Possible electron-density profiles of rehydrated nerve myelin at a resolution of 8 Å are shown.

Comparison of aortic lamellar unit structure in birds and mammals

The structure of the aortic media at different levels in a number of orders of birds has been examined. In general the avian aorta shows a laminar structure, but differs from the mammalian vessel in the occurrence of broad and distinct smooth muscle cell and connective tissue layers in its proximal part. Part of the vessel has a structure which resembles that of mammals; the aorta distal to the origin of the renal arteries is a mixed musculo-elastic structure. Differences between avian and mammalian aortic physiology and their relevance to structural findings are discussed.

Changes in aortic medial elastic structure at different sites in the primates Erythrocebus patas, Macaca irus and Callithrix jacchus.

There is a progressive reduction in the number of lamellar units in the aortic media in these primates as the distance from the aortic root increases. The structure of the media is similar in many primates and this suggests that they may prove suitable animals in which to study mechanical aspects of atherogenesis.

The vasa vasorum patterns in the fetal aorta of sheep.

In 37 aortae of sheep fetuses of various ages, the medial vasa vasorum were investigated. The aortic segments which had more than 29 medial lamellar units displayed medial vasa vasorum. This occurred in the second month of gestation for the ascending and descending segments, and in the fifth month for abdominal aorta.

The effect of injections of lysophosphatidyl choline into white matter of the adult mouse spinal cord.

ABSTRACT The action of lysophosphatidyl choline, LPC, on myelinated fibres in the dorsal white matter of the spinal cord of the adult mouse has been studied electron microscopically, and compared with the recently described activity of LPC in the peripheral nerve fibre. Control injections of sterile isotonic saline and injections of LPC both produced oedematous zones in the white matter; within these zones, many fibres exhibited the characteristic changes of Wallerian degeneration. After injection of LPC, however, an area of demyelination was observed, extending within and beyond the Wallerian degeneration. Ultrastructurally, demyelination involved progressive disruption of the previously-compact sheath, observed initially as a splitting of the intraperiod line within 30 min. Subsequent breakdown was-indicated by the appearance of strands of 4-6 nm repeat lamellar material, itself further degraded through quintuple- and triple-layered lamellar units to disorganized membranous networks around undamaged axons. The significance of the demyelinating activity of LPC is discussed in terms of its known action in in vitro systems of isolated central nervous tissue, and its action in vivo in the peripheral nervous system.

The in vivo and ultrastructural effects of injection of lysophosphatidyl choline into myelinated peripheral nerve fibres of the adult mouse.

ABSTRACT The action of phospholipase A and lysophosphatidyl choline (LPC) on mature, myelinated peripheral nerve fibres has been studied in vivo and electron microscopically, following sub- perineurial injection of these substances. Within 30 min, demyelination was observed in vivo along cylindrico-conical segments, spreading from Schmidt-Lanterman incisures and nodes of Ranvier. By 96 h, all traces of the myelin sheath had disappeared from the area of the lesion, and had been replaced by debris-laden cells lying in chains parallel to one another and the long axis of the fibre. During the next few weeks these cells gradually disappeared, and numerous finely myelinated axons, running between, and in continuity with, the normal fibres proximal and distal to the lesion were observed. If lower concentrations of LPC were used the number of fibres involved decreased, although the demyelinative changes followed the same time-course. Ultrastructurally, demyelination involved progressive disruption and removal of the lamellar sheath, observed initially as a splitting of the intraperiod line within 30 min. Subsequent breakdown resulted in the formation of strands of 4-6 nm repeat material which was further degraded through quintuple- and triple-layered lamellar units to foam-like systems of disorganized lamellar fragments. The Schwann cell and axons appeared to be undamaged by phospholipase A and LPC, and retained their normal impermeability to exogenous ferritin. The significance of the demyelinating capacity of LPC in vivo is discussed in terms of its known action on myelin in vitro, the rapidity and apparent specificity of its action demonstrated in this study, and its potential involvement in pathological demyelination.

The distribution of electron-dense tracers in peripheral nerve fibres.

ABSTRACT Two electron-dense tracers, ferritin and lanthanum, have been administered to peripheral nerve fibres, and their uptake has been studied ultrastructurally. It was found that the peri-neurium was an effective barrier to ferritin in vivo, and the tracer was subsequently injected sub-perineurially. Ferritin uptake over a 120-min period was confined to occasional phagocytic vesicles in perineurial and Schwann cells, and to the nodal gap substance and paranodal peri-axonal space. No uptake was observed in the myelin sheath, incisural intraperiod line gap, or in the axoplasm. Soaking fibres in ferritin in vitro resulted in a more generalized cytoplasmic and axoplasmic uptake, although the myelin sheath and Schmidt-Lanterman incisures remained devoid of the tracer. Lanthanum nitrate, included in the fixative solution, delineated the patent incisural intra-period line gap, and outlined the external surface of the terminal loops of nodal Schwann cell cytoplasm, and the paranodal Schwann cell-axolemmal junction. Unlike ferritin, La3+ penetrated the myelin sheath, being usually confined to the intraperiod line region of the outer lamellae, where it was associated with a widening of the lamellar unit, and an apparent splitting of the intraperiod line. The results are discussed with regard to distribution of extracellular space in peripheral nerve fibres.