Agonist-induced modulation of agonist binding to alpha 1-adrenoceptors in bovine aorta

Prolonged exposure of tissues to hormone agonists results in a subsequent reduction in the sensitivity of the tissue through a process known as desensitization. The desensitization response, either homologous or heterologous, has been shown to be correlated with receptor phosphorylation. Recently we have provided evidence that protein kinase C, when activated by a phorbol ester, regulates alpha 1-adrenoceptor coupling to a G-protein. In the present study, the effects of epinephrine (10 microM) pretreatment on the binding behavior of the alpha 1-adrenoceptor were determined from radioligand binding assays at 25 degrees and 2 degrees C. Pretreatment of tissues with epinephrine for 25 min moderately decreased [3H]prazosin binding by 12% (Bmax 121.5 fmol/mg) in comparison to control (139.3 fmol/mg) with no change in its affinity. The second consequence of desensitization by epinephrine is a decrease in the affinity of agonist binding to alpha 1-adrenoceptors associated with uncoupling of the receptors from the G-protein. In control membranes, at 25 degrees C, epinephrine defined two different affinity states of the receptor, viz. high affinity (KDH 16.5 nM, % RH 21) and low affinity (KDL 710 nM, % RL 79). The high affinity state formed at 25 degrees C is stabilized by forming a ternary complex with a G-protein. Addition of guanylylimidodiphosphate (Gpp(NH)p) reduced the stability of this complex resulting in a loss of high affinity sites in control membranes. On the other hand, epinephrine treated membranes exhibited only a single class of low affinity agonist binding (KDH 659 nM) and further, Gpp(NH)p had no significant effect on binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of clonal vascular smooth muscle cell lines from spontaneously hypertensive and normotensive rat aortas

Vascular smooth muscle cells were isolated from the aortas of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats by use of the explant method on collagen gels. Clonal cell lines derived from these enriched populations possessed ultrastructural characteristics of vascular smooth muscle cells in culture; they grew in hill and valley configuration, immunostained with the muscle actin antibody HHF35, and failed to react with von Willebrand Factor VIII antibody. Fourteen clonal cell lines were characterized for growth and ligand binding characteristics. Large variations in growth rate and cell density at saturation were exhibited by clones of both strains. Similar variability was noted for specific binding of endothelial 1 and Sar1,Ile8-angiotensin II to their receptors, indicating considerable phenotypic heterogeneity among the clonal cell lines. Six selected clones were further characterized for angiotensin II receptor linkage to G proteins. Cells of both strains exhibited comparable affinity shifts in the presence of GTP gamma S. These clonal cell lines should be useful for a variety of analyses of the comparative biology of aortic cells. It is possible that the diversity of phenotypic traits exhibited by these clones reflects the heterogeneity of vascular smooth muscle tissue found in vivo.

Ultrasonic energy. Effects on vascular function and integrity

BACKGROUND

Ultrasonic energy transmitted via flexible wire probes provides a new means of ablating atherosclerotic plaque. We studied the effects of ultrasonic energy (20 kHz) delivered via a ball-tipped wire probe on arterial vasomotor behavior in rabbit thoracic aortas in a perfused whole-vessel model.

METHODS AND RESULTS

After precontraction with phenylephrine (10(-5) M) or KCl (60 mM), the effects of ultrasonic energy (0.7-5.5 W x 60 seconds, 42-330 J) on arterial vasomotor behavior were measured using long-axis ultrasonic vessel imaging of the proximal (ultrasonic probe-treated) and distal (untreated) control segments. The efficacy of plaque ablation at these same probe-tip power outputs was evaluated in atherosclerotic, human cadaver iliofemoral arteries. Ultrasonic energy caused dose (energy)-dependent relaxation in rabbit aortas after precontraction with phenylephrine in arteries with endothelium (n = 8) and without endothelium (n = 8) (p less than 0.001 versus ultrasound treated at power outputs of 2.9 and 5.5 W). There was no difference in the relaxation dose responses between endothelialized and endothelially denuded segments (p = NS). Ultrasonic energy also caused significant relaxation (67 +/- 8%) after voltage-dependent precontraction with 60 mM KCl. Temperature measurements revealed less than 1 degrees C warming of the vessel wall during as long as 2 minutes of treatment at a power output of 5.5 W. Pathological examination showed no smooth muscle injury at (moderate) power outputs that caused arterial relaxation. At probe-tip power outputs of 2.9-5.5 W, ultrasonic energy recanalized two of two totally occluded cadaveric iliofemoral vessel segments. The ultrasonic ablation catheter was also demonstrated to cause arterial relaxation in a recanalized canine femoral artery in vivo.

CONCLUSIONS

Ultrasonic energy delivered via a flexible-wire probe produces dose-dependent, endothelium-independent smooth muscle relaxation capable of reversing both receptor-mediated and voltage-dependent vasoconstriction in vitro. At moderate power outputs, this relaxation response does not appear to be due to thermal effects or irreversible smooth muscle cell injury. This vasorelaxant effect of ultrasonic energy is also apparent in vivo, at doses that effectively ablate atherosclerotic plaque, and may improve the safety of arterial recanalization using ultrasonic energy.

Scanning electron microscopic studies of tissue elastin components exposed by a KOH-collagenase or simple KOH digestion method

A KOH-collagenase or simple KOH digestion method was employed for scanning electron microscope (SEM) studies of elastin components in the rat thoracic aorta, mouse urinary bladder, and human ductus deferens. Immersion of the fixed tissues in 30% KOH solution for 8-10 min at 60 degrees C, with or without subsequent collagenase treatment, successfully removed collagen fibrils and basal laminae while leaving cellular and elastin elements unchanged at their original shapes and locations. The internal elastic lamina of the rat aorta appeared as a solid sheet formed by elastin fibrils 0.1-0.2 microns thick, while the medial elastic laminae were more fibrous because of the presence of numerous fine elastin fibers on their surface. Adventitial elastin fibers were of a cord-like shape complicatedly entangled among the adventitial fibroblasts. These fibers were seen as bundles of fibrils 0.1-0.2 microns thick. In the mouse urinary bladder, elastin formed a thin lace-like sheet just beneath the serosal covering of the peritoneum. This sheet was composed of small bundles of fine (0.1-0.2 microns thick) fibrils. The external connective tissue of the human ductus deferens was made up of a three-dimensional loose network of elastin fibers 0.1-1.5 microns thick. These fibers also appeared as bundles of the fine fibrils. These findings indicate that the present method is useful for SEM studies of elastin as well as cellular components in various tissues and organs. This study also maintains that elastin fibers and laminae are basically composed of unit fibrils of 0.1-0.2 microns thickness. As elastin components are arranged specific to individual organs and tissues, it is reasonable that these components are concerned in the characteristic mechanical properties of these tissues and organs.

Some degree of overlap exists between the K(+)-channels opened by cromakalim and those opened by minoxidil sulphate in rat isolated aorta

The effects of the K+ channel opening drugs minoxidil sulphate and cromakalim, on 42K+ and 86Rb+ efflux and on vasorelaxation in rat isolated aorta, were compared. In rat aortic rings precontracted with noradrenaline (100 nmol/l), minoxidil sulphate and cromakalim concentration-dependently inhibited induced tension by up to 90%, with pD2 values of 7.35 +/- 0.1 and 7.17 +/- 0.1, respectively. Glibenclamide (300 nmol/l), produced 2200- and 19-fold rightward shifts in the concentration-relaxation curves to minoxidil sulphate and cromakalim, respectively, without an effect on the maximum relaxation. Both minoxidil sulphate and cromakalim increased the efflux of 42K+ and 86Rb+ from aorta in a concentration-dependent manner, with midpoints in the mumol/l range; the maximum efflux induced by minoxidil sulphate being approximately one tenth of that induced by cromakalim. The ratio of stimulated 86Rb+/42K+ efflux increased from 0.22 to 0.48 with increasing cromakalim concentrations, but was approximately constant (approximately 0.39) when the minoxidil sulphate concentration was varied. In the presence of minoxidil sulphate, the effects of cromakalim on 42K+ and 86Rb+ efflux were inhibited in a concentration-dependent manner, by up to 60%. In the continuing presence of cromakalim (300 nmol/l), minoxidil sulphate (10 mumol/l)-induced increases in 42K+ and 86Rb+ efflux were inhibited by 45%, whereas conditioning with cromakalim (1 mumol/l) inhibited the 86Rb+ efflux stimulated by additional superfusion of cromakalim (1 mumol/l) by 85%. Glibenclamide inhibited minoxidil sulphate (10 mumol/l)- and cromakalim (1 mumol/l)-induced increases in 42K+ and 86Rb+ efflux in a concentration-dependent manner with IC50 values of approximately 80 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Lovastatin prevents the impairment of endothelium dependent relaxation and inhibits accumulation of cholesterol in the aorta in experimental atherosclerosis in rabbits

STUDY OBJECTIVE

The aim was to determine the effect of the HMG CoA reductase inhibitor, lovastatin, on the loss of endothelium dependent relaxation and the accumulation of cholesterol in the aorta produced by feeding a diet enriched with cholesterol.

DESIGN

The study was conducted in two stages. In stage 1, New Zealand white rabbits were randomised into four groups. Group 1 (n = 15) was fed standard rabbit diet for 6 weeks. Groups 2 (n = 15), 3 (n = 12), and 4 (n = 12) were fed standard rabbit diet supplemented with 2% cholesterol for 2 weeks followed by standard rabbit diet only for the next 4 weeks. In addition, lovastatin (4 mg.kg-1.d-1) was given for the entire 6 weeks in group 3 and for the first 2 weeks only in group 4. In stage 2 a second group of animals was fed a diet supplemented with 0.5% cholesterol for 2 weeks in order to match the serum cholesterol levels in groups 3 and 4 of stage 1.

EXPERIMENTAL MATERIAL

Aortic tissue was removed for measurement of cholesterol content, endothelium dependent relaxation (to acetylcholine), contractile responses (to noradrenaline), relaxant responses (to sodium nitrite), and sudan staining. Serum was obtained for measurement of cholesterol and triglyceride concentrations.

MEASUREMENTS AND MAIN RESULTS

In stage 1, at the end of 2 weeks, the serum cholesterol was significantly lower in groups 3 and 4 than in group 2. At 6 weeks, endothelium dependent relaxation to acetylcholine (-6.0 log mol.litre-1) was impaired in group 2 compared to the other groups: group 1 78.5(SEM 5.0); group 2 43.5(7.8)%; group 3 79.4(4.6)%; group 4 84.7(3.4)%. The relaxant response to sodium nitrite was not impaired in group 2. Further, the aortic tissue cholesterol concentration in group 2 was significantly greater than that in group 1, at 355(65) v 105(10) nmol.mg-1 protein. In groups 3 and 4, the aortic cholesterol concentrations were significantly lower than those in group 2, at 74(4) and 94(17) nmol.mg-1 protein respectively. In stage 2, the serum cholesterol values were matched to those in groups 3 and 4 of stage 1. In these animals, after a further 4 weeks the aortic cholesterol was significantly greater than in group 3.

CONCLUSIONS

Lovastatin attenuates the accumulation of cholesterol and preserves endothelium dependent relaxation in this model of experimental atherosclerosis. It is likely that the latter is a secondary phenomenon.

Immunoelectron microscopic localization of elastic tissue components in archival tissue samples

Tissue samples that have been stored for many years, in different media and under a variety of conditions, have been examined by modern techniques of immunoelectron microscopy, using antibodies against elastic tissue components. A range of postembedding restorative procedures has been identified, which will allow reliable immunolocalization of antibodies against the elastic tissue component of such specimens. These methods have been applied successfully to autopsy-derived material, fixed in buffered formaldehyde, to archival material stored frozen at -70 or -20 degrees C, to specimens fixed for electron microscopy and stored for many years in buffer, and even to archival material from formaldehyde-fixed, paraffin-embedded blocks, reprocessed for electron microscopic examination. The successful restorative methods included pre-treatment of the sections with 6 M guanidine hydrochloride, or 1 M Tris/saline, each containing 100 mM dithiothreitol (a reducing agent) followed by alkylation with 220 mM iodoacetamide. The application of these techniques allowed reliable study of elastic tissue antibody distributions in archival tissues that could not be obtained again, as well as comparative studies with tissues processed many years previously.

Intercellular contacts in the media of the thoracic aorta of rat fetuses treated with beta-aminopropionitrile

Beta-aminopropionitrile (BAPN) alters the scleroproteins of the arterial media in a way which permits an increase in the stress (force/unit area) applied to smooth muscle cells at a given pressure. Pregnant Sprague-Dawley rats were treated with BAPN and the thoracic aortas of exposed fetuses were studied by electron microscopy and image analysis. Transmission electron microscopy of the media of the thoracic aorta revealed that the types of intercellular contacts seen in the controls and in the BAPN group were intermediate junctions (IJs), nexus junctions (NJs), simple appositions (SAs), and interdigitations (Ids) as in adult vessels. The BAPN-treated animals showed an increased density of IJs, SAs, and Ids when compared with controls but the NJs demonstrated no change. Load-sensitive intercellular contacts have been considered to be the major route by which stress is applied across cells, and the increased number in the BAPN group probably represents a response of the vessel wall to increased tangential tension.

[Immunological injury from serum sickness on aortic connective tissue components]

Changes of aortic proteoglycan, collagen and elastic fibers following immunological injury were studied quantitatively and qualitatively under electron microscope after ruthenium red labelling. The results showed that repeated intravenous injections of bovine serum albumin in rabbits activated the synthesis of collagen, elastic fibers and proteoglycan in the aortic wall. The increase of connective tissue components was coincident with the morphological changes of smooth muscle cell.

Method of removal of aortic endothelium affects arachidonic acid metabolism and vascular reactivity

To assess endothelium-dependent responses of blood vessels in vitro, endothelial cells are removed by a variety of mechanical means. We sought to determine if the method of removal of the endothelium affected arachidonic acid metabolism and vascular reactivity of isolated strips of rabbit aorta. Thoracic aorta of New Zealand White rabbits were excised and sectioned into strips with a sharp razor blade. The luminal surface of the vessel was then gently stroked (denuded-1) or forcefully rubbed (denuded-2) with a moist cotton swab. Vessels were then either fixed in 3% glutaraldehyde and processed for electron microscopy, incubated with [14C]arachidonic acid and 20 microM A23187 for determination of arachidonic acid metabolism, incubated with 20 microM A23187 for measurement of endogenous release of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and 12-hydroxyeicosatetraenoic acid (12-HETE) by specific radioimmunoassays, or suspended in an organ chamber filled with Krebs bicarbonate solution for vascular reactivity experiments. Electron micrographs showed that denuded-1 vessels lacked an endothelial cell layer and had slight degeneration of the smooth muscle cells. Additionally, these vessels had a diminished capacity to produce 6-keto-PGF1 alpha as compared to control vessels (214 +/- 25 vs. 360 +/- 36 pg/mg of tissue, P less than 0.05). Denuded-2 vessels contained severe degeneration and rupture of smooth muscle cells in addition to the loss of the endothelial cell layer. While the 6-keto-PGF1 alpha concentration (168 +/- 23 pg/mg) was less in denuded-2 vessels, HPLC indicated that the production of [14C]12-HETE was markedly increased in these vessels as compared to control or denuded-1 vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of lipid microspheres incorporating prostaglandin E1 to vascular lesions

The intravascular distribution of 0.2 mu lipid microspheres (LM) containing prostaglandin E1 (lipo-PGE1) injected intravenously in spontaneously hypertensive rats (SHR) and arteriosclerotic rabbits was investigated by electron microscopic observation and quantification of radiolabelled compounds. LM were observed under an electron microscope to concentrate in subendothelial space of vascular walls, particularly in vascular lesions associated with hypertension or arteriosclerosis. Radiolabelled lipo-PGE1 accumulated more densely in the vascular walls than did free PGE1, and the difference was more conspicuous in vascular lesions. This indicates that lipo-PGE1 penetrates vascular endothelium and then accumulates in blood vessels to result in augmentation of the pharmacological action of prostaglandin. These findings suggest the usefulness of LM as a carrier of prostaglandin to vascular lesions.

Smooth muscle of rabbit isolated aorta contains the NK-2 tachykinin receptor

Neurokinin A, neurokinin B and substance P caused concentration-related contractions of rabbit isolated aorta with pD2 values of 8.1, 6.9, and 6.0, respectively. [D-Pro2, D-Trp7, 9]-substance P, a competitive tachykinin antagonist, had pA2 values of 5.3 against neurokinin A, 5.1 against neurokinin B and 5.2 against substance P indicating that tachykinin receptors mediated responses to the agonists. [pGlu5,MePhe8,-MeGly9]-substance P 5 - 11 (DiMe-C7), senktide and septide did not contract the aorta. It is concluded that of the known tachykinin receptors smooth muscle of the rabbit isolated aorta contains only the NK-2 type.

[Structure of the endothelium of the thoracic and abdominal aorta of intact rats studied by various methods of preparation and handling of the specimens]

By means of scanning and transmissive electron microscopy structural peculiarities of endothelium of the thoracic and abdominal parts of the intact rat aorta have been studied at various regimens of preparation and making specimens . The greatest changes endotheliocytes (EC) undergo at using immersion fixation after dissection of the aortal segments. These changes are less pronounced at immersion fixation in situ. A decreased perfusion pressure results in appearance of intimal folds and microfolds on the surface of EC. Increasing time for washing more than 1 min results in appearance of inflations and craters on the surfice of EC. For analysis by means of transmissive electron microscopy it is not necessary to remove blood completely out of the vascular bed. The most essential factor is to maintain perfusion pressure at the average systolic level in the given area of the vessel. However, to make the analysis by means of scanning electron microscopy this method is not suitable. The most optimal condition for initial stages of preparing vessels for morphological investigation is their washing for 1 min in the medium 199 with addition of heparin (10 units/ml) during no more than 1 min with a subsequent perfusive fixation in 2.5% solution of glutaraldehyde in the medium 199 no less than 5 min under the average arterial pressure in the given area of the vessel.

Changes of beta-adrenoceptors in the aortic muscle cells of spontaneously hypertensive rats

The characteristics of [125I]monoiodocyanopindolol (ICYP) binding to beta-adrenoceptors of cultured aortic smooth muscle cells derived from 4-week-old spontaneously hypertensive rats (SHR) and the Wistar-Kyoto normotensive rats (WKY) were examined. During optimization of the binding assays, we found that the specific binding of ICYP by intact cells was masked by a high level of nonspecific ICYP accumulation in intact cells presumably owing to the lipophilic nature of ICYP. Optimal specific ICYP binding requires that the cells be gently lysed with hypotonic dilution followed by a freeze-and-thaw cycle. Under most experimental conditions tested, the total number of ICYP binding sites in WKY aortic muscle cells was considerably and consistently smaller than that in SHR cells. There was no difference in the Kd values for ICYP binding to SHR and WKY cells. However, when ICYP binding was carried out using crude membrane fractions with well-defined plasma membrane content isolated from aortic muscle strips of adult rats, we found no difference in the number of beta-adrenoceptor sites between SHR and WKY. Morphological evidence indicated that cultured SHR aortic muscle cells contained a greater proportion of larger cells with multinuclear features. These results suggest that an increase in the number of beta-adrenoceptor density per cell in SHR may be associated with cellular hypertrophy of aortic smooth muscle cells. We conclude that under cultured conditions, a higher incidence of polyploid smooth muscle cells in the SHR as compared with WKY was expressed earlier than under in vivo conditions. Therefore, the interpretation of results obtained from cultured cell studies in relation to under in vivo conditions should be exercised with caution.

Histological framework of lymphatic vasa vasorum of major arteries: an experimental study

We investigated the histological framework of lymphatic vasa vasorum of major arteries in the rabbit and guinea pig combining the "natural filling method" with light and transmission electron microscopy. An absorbing adventitial lymphatic network consisting of large and sparsely distributed vessels with capillary structure occupied a more external arterial wall position than blood capillaries. The latter were smaller, more numerous, densely distributed, and located closer to the arterial lumen at the media-adventitial border. Periarterial lymphatics (with the structure of absorbing lymph vessels) encircled the wall of the major arteries and formed a rich and irregular plexus. The topography and anatomic structure of these absorbing lymph vessels suggest that lymphatic drainage plays a significant role in large arterial wall homeostasis.

Early changes in fine structures of the aortic arch in hamsters fed a high cholesterol diet

Intimal changes at the prelesional stage of atherosclerotic lesions were investigated ultrastructurally using hamsters fed a high cholesterol diet for 1 day to 1 month. Observations were restricted to the lesion-prone area in the aortic arch. The endothelial cells began to show well-developed rough endoplasmic reticulum and Golgi apparatus after a few days of the cholesterol diet. After three days, macrophages which contained a few lipid droplets were observed just below the endothelium. We found that the intimal smooth muscle cell formed a gap junction with the process of the medial smooth muscle cell. After a few weeks to 1 month on the diet, the intima became markedly thickened and filled with dense extracellular matrices. The intimal smooth muscle cells showed well-developed rough endoplasmic reticulum and Golgi apparatus with immature granules, suggestive of high secretory activity. The present study showed that endothelial ultrastructural changes, macrophage invasion, and medial smooth muscle cell migration are very early events occurring within a few days after cholesterol intake commences.

Effect of ethane-I-hydroxy-I, I-diphosphonate on arterial calcinosis induced by hypervitaminosis D: a morphologic investigation

The present study was undertaken to examine changes in vascular ultrastructure of rats subjected to hypervitaminosis D with or without treatment with ethane-I-hydroxy-I, I-diphosphonate (EHDP). Five groups of rats were studied. Untreated rats were given 0.9% NaCl i.p. Sham-treated rats were given vehicle (corn oil). Treated rats were given ergocalciferol (75,000 IU i.p.) dissolved in vehicle with or without EHDP (5 mM/100 g body-weight i.p.). Rats which had been given ergocalciferol without EHDP developed hypercalcemia and demonstrated significant arterial calcinosis. A similar degree of calcinosis was not observed in rats given ergocalciferol with EHDP. EHDP appeared to inhibit arterial calcinosis; however, it did not affect plasma calcium levels. This suggests that EHDP might delay calcium influx into the cell and thereby prevent calcium overload. Our findings support the suggestion that EHDP therapy can be an effective treatment for the inhibition of dystrophic arterial calcinosis.

Comparative angiotoxic responses of avian and rodent species in vivo: implications in atherogenesis

As the intrinsic susceptibility to atherosclerosis differs among several taxonomic groups, the present studies were conducted to compare the angiotoxic responses of atherosclerosis-susceptible (quail) and -resistant (rat) animals to allylamine, a selective cardiovascular toxin. Japanese quail (125-150 g) and Sprague-Dawley rats (175-200 g) were gavaged daily for 1, 7, or 20 d with allylamine HCl (0.7, 7, and 70 mg/kg) or tap water. At the ultrastructural level, subchronic exposure of quail and rats to allylamine was associated with dose- and time-dependent disruption of the structural integrity of aortas. These alterations correlated with fluctuations in the nonprotein thiol content of avian and rodent vessels. Angiotoxicity was not associated with alterations in serum cholesterol content. At all times and doses tested, quail were more susceptible than rats to the angiotoxic effects of allylamine. Although the avian sensitivity to toxic insult was greater than that of rodents, quail aortic homogenates bioactivated allylamine to a lesser extent than rat homogenates. Collectively, these results suggest that the aortic sensitivity to toxic insult in avian and rodent species correlates with their intrinsic susceptibility to vascular injury.

Light and electron microscopy of the spontaneous intimal thickenings of rabbit aorta. A normal arterial wall growth

A light and electronmicroscopic study in the intima of the smaller and larger curvatures of a healthy rabbit aortic arch was performed. In both curvatures there were areas of intimal thickenings of varying width, and consisting mainly of collagenous and elastic fibers and smooth muscle cells. The structure of the wider thickenings resembled the media layer. There was evidence that such intimal thickenings are media growth in thickness and physiological in nature. It is inferred that the early lipid deposition in the intimal thickenings of the smaller, but not in the larger curvature, is not related to morphological differences, since both curvatures had the same intimal pattern.

A comparison of the size of fenestrations in the internal elastic lamina of young and old porcine aortas as seen with the scanning electron microscope

The size of the fenestrations (windows) in the internal elastic lamina (IEL) of arteries may be important in the functioning of the blood vessel wall. The fenestrations are filled with collagen, muscle, and (or) ground substance, which must be removed to make the fenestration visible with the scanning electron microscope. All of the nonelastic components are removed with a hot alkali solution. Our experiments were designed to compare the fenestration size in the IEL of the thoracic aorta of young (6-8 weeks) and old (6-9 months) pigs. A protocol for digestion of young pig tissue was developed and showed that fresh young aortas should be digested in 0.1 M NaOH at 75 degrees C for 2 h and fixed tissue should be digested for 5 h. The average area of the fenestrations for young pig thoracic aortas digested for 2 h was 1.8 +/- 0.29 (SE) microns 2 and for the old pig aortas digested for 2 h was 1.7 +/- 0.11 (SE) microns 2. These values were not significantly different (p greater than 0.05), but the IEL from young pigs appeared rougher than the previously reported smooth IEL of the adult pigs.

Ultrastructure of hypertensive rat aorta. Increased basement membrane-like material

To determine the effect of elevated blood pressure on the ultrastructure of rat aorta, hypertension (average mean pressure 163 +/- 17 mm Hg) was produced by suprarenal aortic coarctation. After 3 weeks, the subendothelium of the hypertensive thoracic aorta showed significantly increased volume measurements for mononuclear leukocytes and basement membrane-like material compared with the sham-operated control group. Focal areas of rarefaction of the subendothelial extracellular material were associated with the nearby presence of mononuclear leukocytes. None of these alterations were found in the normotensive abdominal aorta. The tunica media of hypertensive thoracic aorta also contained significantly increased basement membrane-like material. This new finding in an animal hypertension model is the direct result of the quantitative morphological approach employed in this study. In some rats, the partially constricting aortic ligature compromised the right renal artery leading to ischemic atrophy of the right kidney and hyperreninemia in addition to hypertension. In this group, excluded from the previous analysis and evaluated separately, subendothelial thickening and accumulation of basement membrane-like material in the thoracic aorta were greatly increased compared with the control group and other hypertensive rats. This result could not be attributed to an effect of blood pressure alone and might have been caused in part by humoral factors. Basement membrane accumulation appears to be an important early response of the arterial wall to hypertension or other factors in this rat model.

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 that may be the microfibrillar fraction of elastic tissue.

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.

Immunohistochemical demonstration of tyrosine hydroxylase, serotonin and neuropeptide tyrosine in the epithelioid cells within arterial walls and carotid bodies of chicks

By immunolight and electron microscopy, the epithelioid, granule-containing cells within the wall of circumscribed portions of the thoracic aorta, the common carotid artery, the carotid body artery and those composing the carotid body itself of newly hatched chicks were shown to contain serotonin (5-HT), neuropeptide tyrosine (NPY) and tyrosine hydroxylase (TH). No nerve fibres immunoreactive for any of these three substances were found in relation to the granule-containing cells. All the granule-containing cells were immunoreactive for 5-HT. The proportion of 5-HT cells simultaneously immunoreactive for NPY or TH in the total cell population varied in different portions of the arteries and the carotid body: NPY-immunoreactive cells were more numerous in the thoracic and common carotid arterial walls, while TH-immunoreactive cells were much more numerous in the carotid body. Since the granule-containing cells within the arterial wall, because of similarities in their anatomical features to the carotid body, are presumed to function as the arterial chemoreceptor, the difference in content of the amines and peptides among the granule-containing cells in different locations may reflect some differences in the chemoreceptive mechanism between the cells in different locations along the thoracocervical arterial tree.

Age-associated ultrastructural changes in the aortic intima of rats with diet-induced hypercholesterolemia

The ultrastructure of the aortic intima and serum lipid levels in Fischer 344 rats were examined at the ages of 12, 18 and 24 months after feeding the animals an atherogenic diet (2% cholesterol, 0.25% sodium cholate, 5% beef fat) for 6 months. Structural changes in the intima were noticeable only at the age of 24 months. In control rats, the endothelial cells were irregular in shape and each had a well-developed Golgi complex and a few lipid droplets. Simultaneously, reticular, basal lamina-like material and electron-dense granules of extracellular liposomes accumulated in the subendothelium. In fat-fed rats, these structural changes were more conspicuous in association with hypercholesterolemia, and numerous monocytes with lipid droplets were attached to the endothelium, occasionally invading into the subendothelium. Slight foam cell lesions were evident in the intima. The finding that older rats were more susceptible to the atherogenic diet suggests that atherogenesis in the rat is promoted by intrinsic age-associated changes in the aortic intima.