The significance of endothelial stomata and stigmata in the rat aorta. An electron microscopic study

Perfusion of arteries with dilute silver nitrate produces in the endothelium (a) a pattern of pericellular black lines, which we earlier interpreted as a marker of the physiological electrolyte pathway (Zand et al. 1982), and (b) focal black deposits on or between the cells, either ring-shaped (stomata) or solid (stigmata). The purpose of this study was to clarify the nature and significance of these controversial structures. A glutaraldehyde-fixed normal rat aorta was perfused with silver nitrate; 17 typical stomata and stigmata were photographed en face, then studied on ultrathin serial sections. When seen en face, they fell into three groups: (I) 4 stomata in endothelial cells; (II) 6 stigmata in endothelial cells; (III) 7 stigmata on intercellular junctions. By electron microscopy, (I) all the stomata in endothelial cells corresponded to myoendothelial herniae. (II) Of the 6 stigmata in endothelial cells, 4 corresponded again to myoendothelial herniae, 2 corresponded to blebs (it seemed likely that these blebs had existed in vivo, but the possibility of a fixation artefact could not be excluded). (III) Of the 7 stigmata on intercellular junctions, one corresponded to the diapedesis of a mononuclear cell; the other 6 did not correspond to visible endothelial changes and are best interpreted as points of normally higher permeability. We conclude that stomata and stigmata (under the conditions of our experiments) can be explained in at least 4 different ways, depending in part on their location (in cells, on junctions). These ancient terms therefore remain useful for descriptive purposes, as long as it is realized that their significance in any given case must be determined by electron microscopic study.

Adriamycin impairs phagocytic function and induces morphologic alterations in human neutrophils

Normal human polymorphonuclear leukocytes (PMNL) were preincubated in vitro with methotrexate, 5-fluorouracil, vincristine, cisplatin, Adriamycin (doxorubicin), and daunomycin for 15 hours before being tested in a phagocytic-bactericidal assay. Anthracycline-treated PMNL were defective in phagocytosis and killing of the bacteria, in contrast to the other chemotherapeutic agents which allowed the PMNL to remain functional. The defect of Adriamycin-treated PMNL resulted from decreased ingestion: 3 micrograms/ml Adriamycin inhibited by 50% of the uptake of Oil Red-O particles. In this assay, the proportion of noningesting PMNL increased from less than or equal to 20% with 0.62 micrograms/ml to greater than or equal to 90% with 10 micrograms/ml Adriamycin. Electron microscopy revealed that Adriamycin-inactivated PMNL had rounded up, were depleted in glycogen, and had undergone profound nuclear changes. RNA and protein synthesis in PMNL were also affected. Adriamycin, besides producing neutropenia, may decrease the phagocytic function of circulating PMNL.

Studies on the pathogenesis of atherosclerosis. I. Adhesion and emigration of mononuclear cells in the aorta of hypercholesterolemic rats

In rats with diet-induced hypercholesterolemia, two concomitant changes began to occur within 1 week and persisted for 1 year: an increase in total plasma cholesterol and an increase in the number of mononuclear cells adhering to the aortic intima (up to values 50 times normal). Adherent cells were approximately 90% monocytes and approximately 10% lymphocytes. Adhesion was focal, with some preference for ostia of aortic branches; it was followed by migration into the subendothelial space. The subendothelial monocytes/macrophages progressively became foam cells, thus giving rise to microscopic "fatty streaks." Ultimately, typical atherosclerotic plaques were formed. Four possible mechanisms of increased cell adhesion are suggested. Endothelial changes were mild; myelin figures arising from the endothelial surface were seen by electron microscopy. Endothelial denudation was never observed, neither in light-microscopic preparations stained with AgNO3 nor by ultrastructure. Platelet participation was minimal. It is concluded that in this model atherosclerotic plaques are initiated by mononuclear cell adhesion and emigration; endothelial denudation is not a necessary step in their pathogenesis.

The intracerebral microcirculation of the rat in hemorrhagic shock

The intracerebral microcirculation of the isocortex was studied in unanesthetized rats under hemorrhagic shock. To observe the microvessels, three markers were separately injected intravenously during the shock period: (a) Evans blue for fluorescence microscopic visualization of the vessels. (b) India ink for gross and light microscopic evidence of retention of carbon. (c) Horseradish peroxidase (HRP) for light and electron microscopic study. Lack of spontaneous recovery from shock was associated with: (a) 55-65% blood loss, a low blood pressure (30-40 mm Hg), and a dramatic increase in pulse rate; (b) marked Evans blue fluorescence along the vessels; (c) no retention of India ink in the microcirculation; (d) peroxidase activity on the luminal surface of the endothelium. Absence of India ink in the microcirculation of the isocortex during the shock period, as shown by light and electron microscopy, suggests that there is sufficient cerebral blood flow to clear the carbon particles from the blood stream and that there are no openings greater than 30 nm in the endothelial layer allowing seepage of carbon particles through or between endothelial cells. Vascular Evans blue fluorescence and peroxidase activity were both demonstrated on the luminal surface of the endothelial cells, by light microscopy, indicating that these markers are abnormally retained. Ultrastructural demonstration of increased HRP uptake and adherence onto the endothelial cells confirms these observations. These results show that regional endothelial alterations occur in this model of hemorrhagic shock.

Vascular labelling with monastral blue B

Vascular labelling is an established technique of experimental pathology whereby leaky vessels can be identified in vivo. A suspension of a suitable colloidal pigment is injected intravenously; the pigment is then trapped in the wall of the leaky vessels. The colloidal preparation of carbon black, which has been used for many years for this purpose, is no longer commercially available. This communication introduces a substitute: Monastral blue B which gives beautiful preparations in whole mounts, is readily visible in paraffin and plastic embedded histologic sections, has a distinctive appearance in electron micrographs, and is nontoxic in the required dosage.

Endothelium and "silver lines". An electron microscopic study

The significance of endothelial "silver lines" was studied by TEM in rat aortas after perfusion with glutaraldehyde followed by silver nitrate. Standard TEM technique proved unsatisfactory (coarse silver granules, imprecise localization, artefacts). Exposure of the silver-treated aortas to photographic fixer markedly improved the image of the deposits leaving fine, stable, uniform "residual granules" about 100 A in diameter. Most of these granules were localized along the intercellular junctions; they also tended to pool in the basement membrane beneath each junction. This image suggests that the Ag+ ions pass through the junction, and react with its contents as well as with the basement membrane beyond it. A scheme is proposed to explain the reaction of Ag+ ions with anions and negatively charged radicals within the junction. It is concluded that the "silver lines" represent not only a histochemical effect, but also the visualization of a transendothelial electrolyte pathway.

Hydrodynamic injury of the endothelium in acute aortic stenosis

The acute effects of increased shear stress on the endothelium were studied by reducing the lumen of the rat aorta to 20-25% of normal by means of metal clips. Intimal damage in the stenotic area was assessed by light microscopy after perfusion with AgNo3 and study of the endothelium en face. Most of the endothelium was lost within 3 minutes; the extent of the damage was not increased after 1 hour. Electron-microscopic examination showed that some endothelial cells became permeable to tracers (thorium dioxide and horseradish peroxidase); platelets adhered to the exposed internal elastic membrane. Focal endothelial changes were represented by myelin figures of various kinds arising from the luminal surface and by "cellular ulcers," superficial erosions of the endothelial cells accompanied by localized cytoplasmic changes. These "ulcers" occurred more frequently over the nucleus and near junctions; they have not been described in other forms of arterial injury.

Medial changes in arterial spasm induced by L-norepinephrine

In normal rats, the media of small arteries (0.4--0.2 mm in diameter) previously was shown to contain intracellular vacuoles, identified ultrastructurally as herniations of one smooth muscle cell into another. The hypothesis that intense vasoconstriction would increase the number of such vacuoles has been tested. In the media of the saphenous artery and its distal branch, vasoconstriction induced by L-norepinephrine produced many cell-to-cell hernias within 15 minutes. At 1 day their number was reduced to about 1/10 of the original number. By 7 days the vessel was almost restored to normal. Triple stimulation over 1 day induced more severe changes in the media. These findings suggest that smooth muscle cells are susceptible to damage in the course of their specific function. The experimental data are discussed in relation to medial changes observed in other instances of arterial spasm. Endothelial changes that developed in the same experimental model were described in a previous paper.

Endothelial changes induced by arterial spasm

Prolonged arterial constriction can cause damage to the artery itself. The purpose of this study was to define the intimal changes. Two muscular arteries of the rat were studied by electron microscopy 15 minutes to 7 days after L-norepinephrine had been dripped over the vessels. Endothelial damage was caused by the tight folding of the internal elastic lamina, which mechanically squeezed the cells. As the artery relaxed, the endothelium showed gaps, patches of thinned cytoplasm, and many adhesions between cells on opposite sides of intimal folds. The adhesions involved whole cells of cytoplasmic bridges stretched across the intimal "valleys." They were present up to one day; later they seemed to snap and disappear without causing further cellular damage. A survey of the literature shows that such adhesions can also develop in collapsed arteries postmortem. They explain the endothelial "bridges" previously described by others as a normal intimal structure.

Microcirculatory changes in posttraumatic pigmented villonodular synovitis

The synovium from a case of pigmented villonodular synovitis was examined by light and electron microscopy. The hyperplastic villous processes were found to contain, besides many blood vessels, a dense population of phagocytic cells actively engulfing and digesting the erythrocytes; some of their phagosomes ("siderosome") contained iron-laden micelles sometimes arranged in a crystalline lattice. The synovial vessels were remarkable in two respects: first, there was evidence of endothelial breakdown; second, the basement membranes were strikingly multilayered.

Platelets, fibroblasts, and inflammation: tissue reactions to platelets injected subcutaneously

Evidence from the literature indicates that platelets contain (besides mediators of acute inflammation) factors capable of stimulating fibroblastic growth: namely, serotonin and "platelet factors" demonstrable by their effect on tissue cultures of fibroblasts. The purpose of this study was to find out whether an inflammatory and a fibroblast-stimulating effect could be demonstrated in vivo, in the rat, using a single subcutaneous injection of concentrated platelets (platelet pellet). For comparison, rat brain, heart, and kidney tissue were homogenized under sterile conditions, spun down, and injected subcutaneously. Platelet pellets caused intense edema and neutrophil infiltration; after 8 days they had assumed a spherical shape and were surrounded by typical myofibroblasts. The 30 pellets of tissue homogenates induced a much milder acute inflammatory reaction; only one (a heart pellet) induced a recognizable myofibroblast reaction. The delayed appearance of myofibroblasts around platelet pellets was probably mediated by the neutrophils, which accumulated in large amounts around platelet pellets. Using this in vivo model, a direct fibroblast-stimulating effect of platelets was not demonstrable. It is pointed out that there are analogies between cellular reactions induced by injected platelet pellets and by intravascular platelet thrombi.

Lymphocytes and monocytes in the aortic intima--An electron-microscopic study in the rat

In an electron-microscopic survey of the aorta in the adult rat, white blood cells were found adhering to the intima; these were invariably lymphocytes or monocytes. Similar cells were also found beneath the endothelium. Counts were not made, but published data indicate that mononuclear cells lying over or within the rat aortic intima are approximately 1 for every 9 endothelial cells. This infiltration by blood-borne cells is interpreted as a pathologic event, possibly in response to a chemical message (antigen?) originating from the underlying media.

Billroth and Penicillium

Between 1868 and 1873, a surgeon, Theodor Billroth, performed experiments with cultures of bacteria and molds (which he believed to be two aspects of a single form of life) to investigate their role in "accidental wound diseases." Some of the cultures teemed with rounded microorganisms arranged in chains; Billroth chose to call them streptococci. He also noticed that occasionally, when Penicillium appeared in a culture, bacteria failed to grow; he suggested that Penicillum could have "modified the medium" so as to render it unsuitable for bacterial growth. This may well have been the first observation of the antibacterial effect of Penicillium. Similar experiments were performed by Joseph Lister, who noticed in 1871 that bacteria tended to kill the Penicillium, and by John Tyndall, who described in 1876 a "battle" that could be won by either party.

A myofibroblastic tumor. Infantile digital fibroma (recurrent digital fibrous tumor of childhood)

Infantile digital fibromas are distinctive tumors both clinically and morphologically. A unique light microscopic features in the presence of intracytoplasmic, spherical, eosinophilic inclusion bodies. Previous electron microscopic studies have shown these bodies to consist of fibrils; bundles of fibrils have also been described in the cytoplasm. We have examined one such tumor, confirmed earlier findings, and established that the component cells are typical myofibroblasts. The latter are a variety of fibroblasts first described in granulation tissue; they are endowed with contractile properties and are characterized ultrastructurally by bundles of fibrils containing "dense bodies" such as are found in smooth muscle cells. Since our case is identical to those previously described, we propose that this tumor be called infantile digital myofibroblastoma.

Ultrastructure of the myocardium after pulmonary embolism. A study in the rat

The purpose of this study was to find out whether acute massive pulmonary embolism can produce myocardial changes visible by light and electron microscopy. Ww therefore produced pulmonary embolism in rats using plastic microspheres (diameter, 15 +/- 5 mu). Two experimental protocols were used: lethal embolism, with a dose of microspheres known to kill in 3 to 15 hours (these rats were killed after 1 hour), and sublethal embolism, with a dose compatible with 100% survival (these rats were killed after 24 hours). In both groups, the left ventricle was normal. The right ventricle showed two tyes of changes: a) A distinctive lesion of the myocytes, more diffuse after lethal enbolism and different from the "zonal lesion" of shock. It consisted primarily in a localized shredding of the myofibrillar system; hence, the name shredding is proposed. Earlier stages of this lesion were represented by focal dissolution of the Z line (Z lysis). The pathogenesis of these lesions appeared to be primarily mechanical. b) Necrosis was already apparent at 1 hour and was more extensive after 24 hours. The pathogensis of the necrotic lesions is best explained by a temporary ischemia followed by delayed reflow; a possible potentiating role of endogenous catecholamines cannot be excluded. Most capilaries in the necrotic foci remained functional; this explains the rapid rate of the healing process of such lesions. A comparison is drawn between the observed foci of necrosis and the human myocardial lesions knowns as "miliary infarcts" and "myocytolysis." It is proposed that a factor common to all three is the preservation of the microcirculatory vessels and that our experimental model helps illuminate the pathogenesis of the human lesions. It is concluded that the right ventricle of acute cor pulmonale may develop cellular changes with a complex pathologenesis (mechanical, ischemic, and possibly hormonal). The nature of the changes found in our model could represent the morphologic substrate of right-sided failure; it can be correlated with the electrocardiographic abnormalities found in the comparable human condition.

Effect of occlusion on large vessels. I. A study of the rat carotid artery

The effect of permanent occlusion on the carotid artery of the rat was studied by light and by electron microscopy. A segment between two ligatures was examined at times from 2 minutes to 1 year. Between 2 and 15 minutes after occlusion, the red blood cells adjacent to the wall formed radially arranged rouleaux; within 24 hours the endothelium disappeared, while platelets (despite the lack of flow) accumulated against the denuded elastica. This behavior of formed blood elements may have been the result of electric forces (injury potential). By 3 days, undifferentiated cells were found lining the elastica interna or free in the lumen; they apparently were derived from medial smooth muscle.In the media, by 3 days some smooth muscle cells had become necrotic, while "undifferentiated" cells appeared; strong circumstantial evidence suggested that these were smooth muscle cells which had lost their specific characteristics and had thus become dedifferentiated (a phenomenon also known to occur in striated muscle cells); by 1 month they had matured into smooth muscle, but the media from then on contained fewer cells and more collagen than normal.In the lumen, the undifferentiated cells also matured into typical smooth muscle cells from 15 days onward, while collagen and elastin appeared between them. After 1 month these cells began to accumulate droplets of fat, which thereafter increased in number (at 6 months they were associated with cholesterol clefts) and then declined. This accumulation of fat in smooth muscle cells (also seen in atherosclerosis) was interesting because it occurred in the absence of blood flow.

Cell-to-cell herniae in the arterial wall. I. The pathogenesis of vacuoles in the normal media

Vacuoles were observed by light microscopy in the smooth muscle cells of the media in normal rat arteries. By electron microscopy these vacuoles were limited by two membranes; they usually contained myelin figures, a few organelles (especially mitochondria and microfilaments), and an amorphous background material that varied greatly in density. Morphologic evidence indicates that these structures arise by herniation of one smooth muscle cell into another; it is presumed that herniation occurs during contraction at weak points corresponding to areas where adjacent cells come in close contact. Such cell-to-cell herniae were mostly seen in small arteries (arterioles) with a diameter of 0.4 to 0.2 mm; however, none was found in coronary arteries of this size. This discrepancy suggests that the pathogenesis of cell-to-cell herniae is correlated not only with the caliber of the artery but also with functional demands. (Am J Pathol 87:375-398).