Internal Elastic Lamella Research Articles

Routine argyrophil techniques detect Rickettsia rickettsii in tissues of patients with fatal Rocky Mountain spotted fever

Rickettsia rickettsii, a bacterial tickborne pathogen that causes Rocky Mountain spotted fever (RMSF), stains poorly or not at all with conventional tissue Gram techniques, and contemporary visualization of the pathogen in formalin-fixed, paraffin-embedded tissues has relied almost entirely on immunohistochemical staining methods that are generally limited to specialized research laboratories or national reference centers. To our knowledge, previously described argyrophil-based histochemical techniques have not successfully detected rickettsiae in formalin-fixed, paraffin-embedded tissues. To investigate the ability of standard silver impregnation techniques to demonstrate the occurrence and distribution of R. rickettsii in tissues of patients with RMSF confirmed by molecular and immunohistochemical methods, three widely recognized and commercially available silver impregnation methods (Warthin–Starry, Steiner, and Dieterle’s) were applied to various tissues obtained at autopsy from 10 patients with fatal RMSF. R. rickettsii bacteria were demonstrated in one or more tissues of all patients, using each of the argyrophil-based methods, and appeared as small, dark brown-to-black lanceolate rods, often in pairs and occasionally surrounded by a faint halo. Rickettsiae were identified most consistently in small arteries and arterioles of liver, kidney, and leptomeninges, and were localized predominantly to the cytoplasm of endothelial cells and less often within the internal elastic lamella and smooth muscle of the media. This validation of argyrophilic techniques to detect R. rickettsii demonstrates the utility of inexpensive core histochemical methods in the diagnosis of infectious agents in pathology specimens and may have utility in certain resource-limited settings where RMSF is endemic.

Relation of Internal Elastic Lamellar Layer Disruption to Neointimal Cellular Proliferation and Type III Collagen Deposition in Human Peripheral Artery Restenosis

Smooth muscle cell proliferation and extracellular matrix formation are responsible for disease progression in de novo and restenotic atherosclerosis. Internal elastic lamella (IEL) layer maintains the structural integrity of intima, and disruption of IEL may be associated with alterations in neointima, type III collagen deposition, and lesion progression in restenosis. Nineteen restenotic plaques (12 patients) procured during peripheral interventions were compared with 13 control plaques (12 patients) without restenosis. Hematoxylin & Eosin and elastic trichrome stains were used to measure length and percentage of IEL disruption, cellularity, and inflammation score. Type I and III collagens, smooth muscle cell (smc), fibroblast density, and nuclear proliferation (Ki67) percentage were evaluated by immunohistochemistry. IEL disruption percentage (28 ± 3.6 vs 6.1 ± 2.4; p = 0.0006), type III collagen content (0.33 ± 0.06 vs 0.17 ± 0.07; p = 0.0001), smc density (2014 ± 120 vs 923 ± 150; p = 0.0001), fibroblast density (2,282 ± 297 vs 906 ± 138; p = 0.0001), and Ki67 percentage (21.6 ± 2 vs 8.2 ± 0.65; p = 0.0001) were significantly increased in restenotic plaques compared to de novo plaques. Logistic regression analysis identified significant correlation between IEL disruption and neointimal smc density (r = 0.45; p = 0.01) and with type III collagen deposition (r = 0.61; p = 0.02) in restenosis. Increased IEL disruption may trigger cellular proliferation, altering collagen production, and enhancing restenotic neointima. In conclusion, understanding the pathologic and molecular basis of restenosis and meticulous-guided interventions oriented to minimize IEL damage may aid to reduce neointimal proliferation and the occurrence of restenosis.

Intestinal ischaemia and mesenteric necrosis in a heavy smoker

A 48-year-old man presented to the emergency department with severe left-sided abdominal pain. For several years he had suffered from brief episodes of abdominal pain and diarrhoea, each lasting 1–3 days, but he had not previously sought medical attention for these symptoms. Three months prior to emergency admission, the episodes of pain and diarrhoea had become more frequent, associated with night sweats and rapid loss of ∼10 kg. On admission a CT scan of the abdomen demonstrated a grossly thickened proximal jejunum, with the appearances suggestive of ischaemia. At open laparotomy an ischaemic area was identified over the proximal jejunum, in close proximity to a 60 mm diameter mesenteric nodule. The abnormal area was excised completely and bowel continuity restored with an anastomosis. On histological examination, the excised ischaemic jejunum contained severely ischaemic mucosa and the mesenteric nodule was extensively necrotic. There was widespread vasculopathy of mesenteric and small submucosal vessels. Several medium-sized arteries showed inflammation at the intimal and adventitial aspects, with sparing of the muscular layer of the wall (Figure 1). There was marked fibroblastic intimal proliferation, and the internal elastic lamella appeared intact with no duplication. The inflammatory infiltrate was composed predominantly of lymphocytes, histiocytes and eosinophils, while neutrophils were conspicuously absent. A neutrophil-rich thrombus was seen in the lumen of one of the vessels, but there was no evidence of atheroma, calcification or cholesterol embolism. Vascular abnormalities were seen distant from the ischaemic mesentery and bowel making a primary vasculopathy more likely than secondary changes due to another pathology. The histopathological changes were most consistent with Buerger’s disease, whereas other vasculitides, and in particular polyarteriitis nodosa …

Flow shear stress affects macromolecular accumulation through modulation of internal elastic lamina fenestrae

Background Internal elastic lamella and elastic lamellae serve as barriers for macromolecular accumulation in vascular wall. The function of internal elastic lamella in atherogenesis induced by shear stress has not been well understood yet. In the present study, internal elastic lamella remodeling and transmural accumulation of macromolecules in the arterial wall under altered shear stress were investigated. Methods The ligation of left distal carotid branches induced low shear stress in the left common carotid artery and high shear stress in the right common carotid artery of rats for 7 days. Fenestrae in internal elastic lamella were assessed by confocal microscopy. Horseradish peroxidase accumulation was determined by its transmural concentration profiles. Fibronectin expression was examined by immunohistologic staining and Western blotting. Findings Low shear stress significantly decreased the percentage of fenestrae area in internal elastic lamella from 15.35% to 8.03% in left common carotid artery, while high shear stress nearly had no influence in right common carotid artery. Comparing with less accumulation of horseradish peroxidase in right common carotid artery, horseradish peroxidase was significantly accumulated in the innermost part of the media, and fibronectin expression increased to 3.3-fold in left common carotid artery. Interpretation Our results suggested that shear stress alteration could influence the endothelial cell function as well as internal elastic lamella and elastic lamellae remodeling. Low shear stress decreased the permeability of internal elastic lamella and elastic lamellae by reducing fenestrae of them, which involved the enhanced fibronectin expression. Therefore, the increased accumulation of macromolecules in the arterial wall was observed. Our data supply new evidence on the mechanisms of atherogenesis induced by low shear stress.

Ultrastructure of intramural coronary arteries in pigs with hypertrophic cardiomyopathy

Pigs with hypertrophic cardiomyopathy diagnosed by echocardiographic examination were selected for study from a genetic breeding herd. Under dissecting microscopic examination, intramural coronary arteries in the septum and left ventricular free wall of euthanized pigs were collected for ultrastructural study. The major lesions of wall thickening included degeneration or denudation of endothelium, subendothelial edema, proliferation of collagen fiber, and hyperplasia of smooth muscle cells. Smooth muscle cells proliferated and migrated through the internal elastic lamella into the intima, which caused the early lesion of wall thickening of the intramural coronary arteries. The extent of smooth muscle cell proliferation was related to the severity of endothelial damage. The smooth muscle cells in the intima were identified by immunohistochemical staining (i.e., smooth muscle actin [SMA] stain). Three major types of severe wall thickening with narrow lumen were observed in the intramural coronary arteries. Edema in the intima caused the major lesion of Type I wall thickening. The internal elastic lamella was broken into small interrupted fragments, and fine fragments of elastic fibers surrounded by the cellular processes of smooth muscle were observed in Type I lesions. Many smooth muscle cells proliferated in the intima and media, which constituted the major lesion of Type II wall thickening of the intramural coronary arteries. Many vacuolized, degenerated smooth muscle cells with fewer sarcoplasmic myofilaments could be clearly observed in the Type II lesions. In advanced cases, severe vacuolization and degeneration of smooth muscle cells with the presence of many bizarrely shaped smooth muscle cells in the walls of the intramural coronary arteries could be observed, which caused the major lesion of Type III wall thickening. Pigs with hypertrophic cardiomyopathy, characterized by spontaneously occurring lesions in intramural coronary arteries, may prove a valuable animal model for human disease.

Arterial changes in paediatric haemodialysis patients undergoing renal transplantation.

The relationship between primary renal disease and arterial wall changes in paediatric haemodialysis patients has been little studied. The aim of the present work was to determine the influence of primary renal disease on arterial wall pathology in uraemic paediatric patients. Twelve paediatric haemodialysis patients (seven girls, five boys) aged 11-17 years were included in the study. The primary renal diseases were urinary malformations in six patients (uropathy group) and acquired glomerular diseases (glomerulopathy group) in six patients. Age, sex distribution, duration of chronic renal failure, duration of haemodialysis, blood pressure, serum glucose, triglycerides, cholesterol, fibrinogen, calcium, phosphorus and parathyroid hormone levels were compared. Internal iliac artery samples were obtained at the time of related-donor renal transplantation. Artery samples were fixed in formaldehyde and sections were stained separately with haematoxylin and eosin, Orcein, Verhoef-van Gieson, and Masson trichrome. Five arteries had fibrous or fibroelastic intimal thickening, medial mucoid ground substance and disruption of the internal elastic lamella. Two of these had microcalcification in the intimal layer; another two demonstrated atheromatous plaques; the remaining five were normal. These pathological changes were found in the arteries of all six patients with uropathy, whereas of the six patients with glomerulopathy only one had arterial changes (P<0.001). The duration of chronic renal failure was 4.8+/-1.9 years in the uropathy group and 2.2+/-1.2 in the glomerulopathy group (P<0.05). The two groups were comparable in terms of serum glucose, triglycerides, cholesterol, fibrinogen, calcium, and parathyroid hormone levels, presence of hypertension, sex distribution, and duration of haemodialysis. Plasma phosphorus and the calcium x phosphate product were higher in the uropathy group than in the glomerulopathy group (P<0.05). This study demonstrated that pathological changes are common in the arteries of uraemic paediatric patients, and that calcification and atherosclerosis are integral to this disease process. In our study, these alterations were more common in the patients with uropathy. We speculate that the patients with uropathy are more prone to these alterations due to slower progression and a longer duration of renal insufficiency.

ACAT inhibitor F-1394 prevents intimal hyperplasia induced by balloon injury in rabbits

Acyl-CoA:cholesterol acyltransferase (ACAT) is thought to contribute significantly to lipid deposition in macrophages, which subsequently leads to the initiation and progression of atherosclerosis. The aim of the present study was to examine the influence of hypercholesterolemia on arterial hyperplasia induced by endothelial denudation and the direct effect of ACAT inhibition on lesion formation. Rabbits were fed either a cholesterol diet or a regular diet for 4 weeks, and then the left common carotid arteries were denuded of endothelium. After the operation, all rabbits were kept on the regular diet for 2;-6 weeks. Two weeks after the denudation, the degree of intimal thickening and the number of proliferating cells (which were immunohistologically identified to be smooth muscle cells) were similar in hypercholesterolemic and normolipidemic rabbits. After that, both parameters progressively increased in hypercholesterolemic rabbits but declined in normolipidemic rabbits. Macrophages were apparent in the lesions only in hypercholesterolemic rabbits. Next, the effect of the ACAT inhibitor, (1S,2S)-2-[3-(2,2-dimethylpropyl)-3-nonylureido] cyclohexane-1-yl 3-[(4R)-N-(2,2,5,5-tetramethyl-1,3-dioxane-4-carbonyl)amino]propionate (F-1394), on neointimal formation in hypercholesterolemic rabbits was examined. Oral administration of F-1394 significantly reduced neointimal thickening and the extent of macrophages in lesions without affecting serum cholesterol levels. These results suggest that hypercholesterolemia causes macrophage-derived foam cell accumulation in lesions, and that the progression of lesions is accelerated by the presence of macrophages. Moreover, the study shows that F-1394 prevents neointimal formation even in the presence of hypercholesterolemia, indicating that F-1394 may be useful for treating restenosis after percutaneous translumenal coronary angioplasty in hyperlipidemic patients.

The development of preatherosclerotic coronary artery lesions in perinatal piglets.

The fine structure and ultrastructure of the anterior descending coronary artery were studied in a series of perinatal piglets at 1 week prior to birth, and at 8, 24, 72 and 168 h after birth. In the anterior descending coronary artery, at or just distal to the branch point of the left circumflex artery, early plaque-like intimal lesions were present in the majority of animals. These consisted of subendothelial edema, fragmentation and dissolution of the internal elastic lamella, and the appearance of intimal myoid cells known as modified smooth muscle cells (MSMCs). These changes were present in all piglets at and before 8 h of age. They persisted and progressed during the first week of life in about half of the piglets. Beginning at 72 h and continuing through 168 h, there was an increase in MSMCs and the appearance of fibroblasts. Both fibroblasts and MSMCs were associated with the elaboration of dense collagen fibrils. Foamy macrophages appeared within the subendothelial intima having the appearance of lipophages. While the prevalence of these changes at birth indicates that they may be part of normal development, their persistence in half the piglets and structural features suggest reaction to intimal injury beginning prenatally. The lesions may be precursive of coronary atherosclerosis later in life and may parallel the early stages of atherogenesis in humans.

Necklace-like detachment of endothelial cell layer from arterial wall under low-calcium condition

The diversified morphological manifestations in various tissues and organs obtained by administration of differing amounts of calcium chelating agents were reported in previous papers (Yamaguchi et al 1981 a & b; 1982; 1990; 1993). In our recent research described here, administration of a moderate dose of Na2EDTA over the short term demonstrated necklace-like detachment from the arterial wall without disruption of the endothelial cell chain. Intercellular spaces in the media just beneath the detached endothelial cell layer was stained strongly with colloidal iron staining. Electron microscopic observation revealed that the detached endothelial cells showed a lot of elongated anchoring villi from the basal surface, usually seen at the luminal surface, adhered to the degenerative and thin flattened internal elastic lamellae. The alteration of the colloidal iron staining of the vascular wall under the low-calcium condition is suggested to be induced by loosening of the molecular structure of glycosaminoglycans (GAGs) as well as glycoproteins (GPs), comprising the important component of the intercellular matrix and elastic lamellae, which would induce a change in their pasty or viscous character. This would be an accelerative factor for detachment of endothelial cells. Moreover, the lack of the waving of the internal elastic lamellae, trapping of endothelial cytoplasmic processes among them, would play the decisive role in the total detachment of the endothelial cell layer. On the other hand, the low-calcium condition did not adversely influence the joining of endothelial cells. The pathognomatic mechanism will be discussed, with a comparison made to the angiolytic changes provoked by a large amount of Na2EDTA.

The relationship between wall tension, lamellar thickness, and intercellular junctions in the fetal and adult aorta: Its relevance to the pathology of dissecting aneurysm

It is known that the distribution of stress and strain in the vessel wall is not uniform. We believe that this explains the location of the plane of dissection in dissecting aneurysms of large elastic arteries. We have investigated the effects of non-uniformity of stress and strain on the thickness of each elastic lamella and on the distribution of intercellular junctions in the media of developing and adult rats, to seek evidence to support this hypothesis. Intercellular junctions were identified by transmission electron microscopy of whole wall sections. A morphometric study of elastic tissue distribution was made on an image analysis computer. Differences were analysed using one-way analysis of variance. There are between six and eight elastic lamellae in the aorta of rats. In the fetus, only the internal elastic lamella is complete; the others were not fully formed by term. In the adult, the inner five elastic lamellae were thicker than the remaining two or three, and smooth muscle cells in the thicker lamellar units had more cell-cell contacts of all types examined. These data support the concept of a difference in stress-resisting properties of the aortic wall on the junctions between the inner two-thirds and the outer third of the media. The findings indicate that, as proposed in theoretical models the innermost lamellae support the high tension. In the adult aorta, the structure is modified to enhance the capacity to resist stress in the internal two-thirds of the media.(ABSTRACT TRUNCATED AT 250 WORDS)

ウサギ頚動脈カフ被包モデルの内膜肥厚におよぼすイコサペント酸エチルの影響

To evaluate the effect of EPA on arteriosclerosis, 24 Japanese white rabbits were studied as cuffsheathed models, which produced diffuse intimal thickening of the carotid artery. They were divided into 4 groups. Groups I and II were fed a normal diet, while groups III and IV were fed with a 0.5% cholesterol diet after cuff treatment. In groups I and III, EPA was administered p.o. forcibly at 600 mg/kg/day 1 week before cuff treatment. The cuff was placed around the carotid artery for three weeks. Then, carotid artery samples were obtained for pathological studies. From the elastica-stained samples, the area of the intima (AI), media (AM), and the part surrounded by the internal elastic lamella (A-IEL) were measured using a digitizer, to calculate AI/A-TEL (IT) and AI/AM (IT-M) as indices of intimal thickening.The mean IT-M in group I (0.14) decreased significantly compared with group II (0.22), which showed cellulofibrous intimal thickening with a partly lacerated IEL. The mean IT in group III (0.30) was also significantly lower compared with group IV (0.46), which revealed prominent intimal thickening with spindleshaped smooth muscle cells. These findings suggested that EPA suppressed intimal thickening, with cell proliferation observed in the early phase of atherosclerosis.

Arteriosclerosis of extramural coronary arteries in labradors with congestive heart failure

ABSTRACTTwo adult male labrador dogs had short clinical histories of congestive cardiac failure lasting only six weeks. Cardiac function deteriorated rapidly in both dogs, in spite of symptomatic treatment with cardiac glycoside, diuretic and p‐adrenergic blocker. Necropsies revealed ascites and pulmonary congestion, but no macroscopic evidence of valvular or myocardial disease adequate to account for the cardiac dysfunction. Both dogs had extensive stenosis of extramural coronary arteries. This unusual vascular lesion comprised fibroelastic intimal thickening, discontinuity of internal elastic lamella and focal atrophy of medial smooth muscle. It seems likely that cardiac failure in these dogs was associated with myocardial underperfusion caused by extensive non‐thrombotic, non‐atherogenic stenosis of extramural coronary arteries.

Formation of a lipid gradient across the human aortic wall during ageing and the development of atherosclerosis

The smooth muscle cell invasion and macrophage stimulation within the intima during prolonged exposure to high blood levels of cholesterol esters contribute to increased production of connective tissue matrix. The thickened intima in turn immobilising more LDL derived lipid from the plasma. With damage to the internal elastic lamellae, from essential hypertension, the absorbed lipid can move down a concentration gradient into the medial tissue. This model was supported by our laboratory finding of a lipid gradient across the aorta wall. The gradient commenced shortly after completion of body growth, when the transmedial gradient became detectable. The slope of the gradient progressively increased during ageing. Association of the lipid medial gradient with the degree of atherosclerotic involvement suggested that the gradient influenced the development of intimal lesions. Accumulation of lipid within the medial tissue may then reduce the inward lipid transfer rate from the intima, promoting increased intimal retention and cause the formation of atherosclerotic plaques from the fat saturated intima.

Spontaneous arterial lesions: Their possible role in arteriosclerosis

Spontaneous lesions of the arterial wall involving the internal elastic lamellae and variable amounts of the intima are described in the spontaneously hypertensive rat caudal, renal, and mesenteric arteries. A simple model for producing similar circumferential lesions in rat and rabbit carotid arteries has been developed and the subsequent repair of these lesions is described. Two types of circumferential lesion can be produced by the application of 50–160 g of longitudinally applied tension. Small lesions can be up to 400 μm in length and are characterized by the loss of a small area of endothelium and rupture of the internal elastic lamellae. No demonstrable damage to the media is detected in these lesions. Larger lesions can be up to 1 mm in length and are characterized by the loss of endothelium and rupture of the internal as well as a variable number of medial elastic lamellae. Little, if any, damage to the medial smooth muscle cells is observed although the extracellular matrix is often disrupted. Small lesions are completely reendothelialized within 24 hr and larger lesions within 7–10 days. Both large and small lesions repair without the formation of an intimal thickening of smooth muscle cells, despite quite marked damage to the media of the larger lesions.

Pathogenetic mechanism of stenosis in the intramural coronary artery.

In order to clarify the pathogenetic mechanism of stenosis in the intramural coronary branch, morphological changes were examined by postmortem coronary angiography and determination of the Coronary Stenosis Index of the Myocardium (CSIM) were made in hearts obtained by autopsy from 10 patients with hypertension, 15 with normotensive myocardial infarction, 25 with hypertensive myocardial infarction, 6 with mitral valvular disease, 7 with aortic stenosis and 14 control subjects. CSIM was significantly higher in patients with hypertension, infarction with hypertension and aortic stenosis than in other three groups, indicating higher incidence of stenosis in those with a left ventricular pressure load. There was no specific correlation between the degree of stenosis of the epicardial coronary artery and that of the intramural coronary branches supplied by the former in any groups examined. Major pathological changes of the intramural coronary branches were muscular hypertrophy of media and proliferation of internal elastic lamella, both observed with a high incidence in vessels with high CSIM values. These findings suggest that intramural pressure which exerted extravascular pressure played an important role in the pathogenetic mechanisms of stenotic changes in the intramural coronary branches.

Studies of hypercholesterolemia in the nonhuman primate. I. Changes that lead to fatty streak formation.

Morphologic studies resulting from events that occur during the development of the lesions of atherosclerosis were studied in chronic, diet-induced hypercholesterolemia in a series of nonhuman primates. Within 12 days of hypercholesterolemia in Macaca nemestrina, monocytes became adherent to the surface of the endothelium. These monocytes appeared to migrate subendothelially, accumulate lipid, and become lipid-laden macrophages (foam cells). Within a month, a "serofibrinous insudate" formed together with variable numbers of subendothelial lipid-laden macrophages. By the second month, foam cells increased in number, often in multilayers, to form a fatty streak. Concomitantly, the luminal surface of the arteries became increasingly irregular due to the subendothelial accumulation of foam cells. Numerous monocytes continued to attach to the endothelial surface over the fatty streaks, and many of them appeared to enter the intima and participate in the growth of the fatty streaks. Lipid-laden smooth muscle cells appeared in small numbers and formed two to four layers between the macrophages and the internal elastic lamella at 2 to 3 months. During the third month of hypercholesterolemia, endothelial cell continuity over the lipid-laden macrophages became interrupted, exposing the underlying foam cells to circulating blood. Foam cells were then readily observed in whole blood smears, suggesting that many of the lipid-laden macrophages leave the intima and enter the circulation. After 4 months, significant endothelial denudation was found in the iliac artery and many exposed macrophages were covered by adherent platelets in the form of a mural thrombus. Thus, the early components of atherosclerosis induced by chronic hypercholesterolemia centered around the monocyte-macrophage and its interaction with endothelium in the induction of the fatty streak. Subsequent changes that lead to macrophage-smooth muscle interactions, platelet-macrophage interactions, and platelet-endothelial interactions appeared to set the stage for the development of more advanced proliferative lesions.

The importance of the subendothelial connective tissue to the permeability of the neointimal barrier

The thoracic aortas from two rabbits that had survived a single embolectomy catheter lesion for 2 years were studied by transmission electron microscopy after vital staining with Evans blue. An intimal thickening was formed inside the original internal elastic lamella in the re-endothelialized areas. Small blue areas in the ventral aortic wall showed intact endothelial cells covering an amorphous structureless subendothelial matrix. These observations indicate that endothelial cells do not form an effective barrier in the absence of differentiated subendothelial connective tissue.

Effects of particle size and perfusate composition on the uptake of colloidal gold by the rabbit thoracic aorta perfused in situ

The influence has been investigated of particle size on the uptake of radioactive gold colloid by the rabbit thoracic aorta perfused in situ. Particles ranging in diameter from 14 nm to 40 nm were suspended in 0.9% NaCl and infused either at a pressure of 15 mm Hg for times of between 2 z and 60 min or at pressure of between 15 and 160 mm Hg for 5 min. Uptake by the whole intima-media increased with perfusion time and hydrostatic pressure but did not depend on particle size. Radioactive assay of serial sections across the aortic wall also showed that particle size did not influence the distribution of tracer. An effect of perfusate composition on uptake was demonstrated in further experiments in which particles either 14 or 40 nm in diameter were suspended in pooled rabbit serum and infused at pressures of between 15 and 140 mm Hg for 5 min. Uptake and transmural distribution were again independent of particle size, but uptake was 4–5-fold less than when the particles were perfused in saline. Under all perfusion conditions radioactivity fell steeply across the intima and then rose gradually across the media and adventitia. Radioactivity in the outer media and adventitia increased with perfusion time but little change could be detected in intimal activity. In transmission electron micrographs, particles in the intima were not seen to penetrate the internal elastic lamella and in the outer media particles remained extracellular and did not enter collagen bundles. Autoradiographs showed that particles in the intima were uniformly distributed around the circumference of the vessel but in the outer media and adventitia particles usually clustered close to the vasa vasorum.

The internal carotid artery does not directly supply the brain in the Monodontidae (order Cetacea).

In this paper we describe the gross and microscopic anatomy of the internal carotid artery and demonstrate that this vessel does not directly supply blood to the brain, in the Monodontidae (order Cetacea). Our account is based on gross dissections and perfusion casts of the arterial vasculature in Delphinapterus leucas and Monodon monoceros and on histological material from the latter species. The internal carotid artery originates low in the neck and extends to the carotid rete at the base of the brain. The vessel tapers dramatically along its cervical course and changes from an artery elastic in nature to one more muscular. A single large cervical branch occurs in D. leucas and supplies cerebrally related retia in this region and prevertebral muscles. No cervical branches occur in M. monoceros. In otic regions, the internal carotid artery is small and muscular. A lumen is present; however, a split internal and external elastic lamella and a thickened subendothelial layer are evident. Though patent in the neck and ear, the vessel appears occluded within the carotid canal. At this level, the vessel is characterized by absence of a lumen and by fragmented elastic lamellae. We conclude that the internal carotid artery is anatomically closed at a level just proximal to the carotid rete and hence has no direct involvement with cerebral blood supply in the Monodontidae. Our results confirm other investigators' work on smaller cetacean species.

Prolonged Prostaglandin E1 Infusion: Histologic Effects on the Patent Ductus Arteriosus

An infant with Ebstein's malformation of the tricuspid valve and severe pulmonic stenosis underwent a 39-day course of prostaglandin E1 infusion, and a histologic study of the ductus arteriosus was undertaken after autopsy. There were marked alterations in the ductal and juxtaductal structures following this prolonged infusion of prostaglandin E1. The internal elastic lamella of the ductus was disrupted in many areas. The media showed widespread areas of disruption with cavity formation. The adventitia adjacent to the junction of the ductus with the pulmonary artery was thickened and infiltrated with mononuclear cells. The nerve trunks in the adventitia were markedly infiltrated with mononuclear cells and showed cavitation as well as considerable surrounding edema. Mucopolysaccharides were increased throughout the ductus. These changes produced increased fragility of the ductal and juxtaductal structures, thus increasing the likelihood of spontaneous aneurysms and rupture, or of tearing or rupture at the aortic and pulmonary junctions at the time of surgical closure of the ductus. Unusual fragility of the ductus, pulmonary artery, and aorta has been observed during ligation of the ductus following prostaglandin E infusions lasting seven and ten days. Additionally, another patient who had received prostaglandin E infusion for six days demonstrated aneurysmal fullness to the ductus arteriosus at autopsy. The histologic findings and intraoperative experience in this study suggest that there may be a real danger of spontaneous or surgically related rupture of the ductus arteriosus after prolonged infusion of prostaglandins.