Pathology of experimental pulmonary bone marrow embolism. I. Initial lesions of the rabbit lung after intravenous infusion of allogeneic bone marrow with special reference to its pathogenesis

In order to investigate the initial lesions of pulmonary bone marrow embolism and its pathogenesis, the author studied the pulmonary changes of 70 rabbits during a 24-hour period after the infusion of 500 mg of fresh allogeneic bone marrow into the marginal ear veins. After 30 minutes, leukostasis was observed in the non-embolized small arteries. After 2 hours, leukostasis increased and by 5 to 10 hours, it reached a maximum, still decreased considerably after 24 hours. In the perivascular connective tissue, edema and inflammatory cell infiltration had occurred as a result of increased vascular permeability due to leukostasis. Fifteen minutes after intravenous administration of a single shot of indomethacin (5 mg/kg), the infusion of allogeneic bone marrow was performed. Five hours after the infusion, the suppression of pulmonary vascular leukostasis and interstitial edema were observed. The effect of drugs on morphological changes, however, is extremely small in the group pre-treated with diphenhydramine hydrochloride (3 mg/kg). The author concluded that the mechanical injury of vascular endothelial cells by emboli and the accumulation of leukocytes in the pulmonary vessels may play an important role in the pathogenesis of the initial change of pulmonary bone marrow embolism. It is also suggested that the embolized bone marrow in the small arteries and vasculitis may lead to arteriosclerosis in the future.     

Pathology of experimental pulmonary bone marrow embolism. II. Post-embolic pulmonary arteriosclerosis and pulmonary hypertension in rabbits receiving an intravenous infusion of allogeneic bone marrow

The author investigated the morphogenesis of pulmonary arteriosclerosis in rabbits at 2 days to 3 months after the infusion of sliced fresh allogeneic bone marrow (500 mg) into the marginal ear vein of 87 rabbits. After 2 to 7 days, granulation tissue was formed in the embolized bone marrow, and new endothelial cells appeared on the surface resulting in recanalization. By 2 weeks, embolized bone marrow developed into fibrous and fibro-fatty plaques in the arterial wall. Moreover, from 4 weeks on, smooth muscle cells and elastic fibers proliferated in the emboli just beneath the new endothelial lining. The intima of non-embolized small arteries showed circumferential fibroelastosis, as the result of arteritis and followed by proliferation of medial smooth muscle cells, with narrowing of vascular lumen. The medial smooth muscle cells play an important role in the morphogenesis of pulmonary arteriosclerosis in bone marrow embolism. Pulmonary arterial pressure gradually increased 1 month as well as 3 months after the infusion. It is considered that narrowing of the vascular lumen resulted from post-embolic pulmonary arteriosclerosis may produce persistent pulmonary hypertension.     

PATHOLOGY OF EXPERIMENTAL PULMONARY BONE MARROW EMBOLISM

The author investigated the morphogenesis of pulmonary arteriosclerosis in rabbits at 2 days to 3 months after the infusion of sliced fresh allogeneic bone marrow (500 mg) into the marginal ear vein of 87 rabbits. After 2 to 7 days, granulation tissue was formed in the embolized bone marrow, and new endothelial cells appeared on the surface resulting in recanalization. By 2 weeks, embolized bone marrow developed into fibrous and fibro-fatty plaques in the arterial wall. Moreover, from 4 weeks on, smooth muscle cells and elastic fibers proliferated in the emboli just beneath the new endothelial lining. The intima of non-embolized small arteries showed circumferential fibroelastosis, as the result of arteritis and followed by proliferation of medial smooth muscle cells, with narrowing of vascular lumen. The medial smooth muscle cells play an important role in the morphogenesis of pulmonary arteriosclerosis in bone marrow embolism. Pulmonary arterial pressure gradually increased 1 month as well as 3 months after the infusion. It Is considered that narrowing of the vascular lumen resulted from post-embolic pulmonary arteriosclerosis may produce persistent pulmonary hypertension.     

家兔急性肺栓塞对肺血管内皮细胞超微结构及血清一氧化氮含量的影响

目的 探讨急性肺栓塞（APE）对肺血管内皮细胞（PVECs）的结构及血清一氧化氮（NO）含量的影响。 方法 19只日本大耳兔,随机分成假手术组、栓塞2 h、4 h组(n=3)和8 h组（n=10）。通过输入自体血栓建立家兔急性肺栓塞模型后,采用HE染色光学显微镜下观察肺的病理组织学变化;透射电子显微镜下观察PVECs在肺栓塞2 h、4 h及8 h的超微结构变化;硝酸还原酶法测定相应时间点血清NO含 结果 HE染色显示栓塞组肺动脉内有血栓,肺间质炎性病变,肺淤血;透射电子显微镜显示,栓塞组PVECs水肿、破裂,线粒体肿胀,内质网空泡化,并随栓塞时间延长PVECs出现坏死脱落,细胞器溶解。肺栓塞2 h、4 h和8 h血清NO含量均低于栓塞前,与栓塞前比较差异有显著性意义（P＜0.05）。 结论 家兔APE可致PVECs超微结构改变和血清NO含量下降,且两者间关系密切。     

Acute effects of Escherichia coli endotoxin on the pulmonary microcirculation of anesthetized sheep structure:function relationships

Infusion of Escherichia coli endotoxin into sheep causes a syndrome analogous to the adult respiratory distress syndrome. Physiologic measurements show an initial phase of marked pulmonary hypertension followed by a phase characterized by the production of large quantities of protein-rich lung lymph. The present study relates the structural changes that occur during endotoxemia to concomitant functional changes. In five anesthetized open-chest sheep, we monitored pulmonary and systemic artery pressure for a 1 hour baseline period and for 4 hours after the start of E. coli endotoxin infusion (1.25 microgram/kg, intravenously). We also measured cardiac output, arterial blood gases and pH, and number of circulating leukocytes. In addition, we sequentially biopsied random lobes from the lungs of each sheep at baseline and at 15, 30, 60, 120, 180, and 240 minutes after the start of endotoxin. Five control sheep were treated identically except that they received saline instead of endotoxin. By 15 minutes after the start of endotoxin infusion, light microscopy revealed margination and accumulation of leukocytes in the lungs' microcirculation. Counts of the number of peripheral lung granulocytes in biopsy specimens showed a 3-fold increase above baseline by 15 minutes and a 6-fold increase by 4 hours. By electron microscopy, the leukocytes were identified as both granulocytes and lymphocytes, present in approximately equal numbers. Some granulocytes were fragmented, and specific granules were found free in the vessel lumen. By 30 minutes, some leukocytes were migrating into the interstitium. By 60 minutes, interstitial edema was seen, and there was focal endothelial cell damage. Correlation of the structural with the physiologic changes shows that the initial accumulation of leukocytes in the microcirculation occurs when pulmonary hypertension develops. The migration of leukocytes into the interstitium and endothelial cell damage precedes the physiologic changes that we interpret as increased pulmonary vascular permeability. Since gram negative septicemia is a frequent occurrence in the adult respiratory distress syndrome the changes described here may be similar to the alterations that occur early in the development of the syndrome in man.     

SK&F 95654-induced acute cardiovascular toxicity in Sprague-Dawley rats--histopathologic, electron microscopic, and immunohistochemical studies

The characteristics and pathogenesis of the cardiovascular toxicity induced by the type III selective phosphodiesterase inhibitor SK&F 95654 were examined in 2 studies. Sprague-Dawley rats received either a single sc injection of 50, 100, or 200 mg/kg SK&F 95654 and were euthanized at 24 hours after administration of the drug (Study 1), or were given a single subcutaneous (sc) injection of 100 mg/kg SK&F 95654 and euthanized at 1, 2, 4, 6, 8,12, 24 hours, or 2 weeks after treatment (Study 2). Control rats received either DMSO or saline. Myocardial lesions and vascular lesions of the mesentery, spleen, and pancreas were seen 24 hours after dosing with either 50,100, or 200 mg/kg SK&F 95654. The frequency and severity of these lesions (evaluated after the 100 mg/kg dose) increased with time over a period of 1 to 24 hours. By 2 weeks, the lesions subsided. Cardiac lesions consisted of myocyte necrosis with hypercontraction bands, inflammatory cell infiltration, interstitial hemorrhage, and interstitial edema. Vascular lesions of the mesentery were most prominent and consisted of vasodilatation and inflammation in the small-sized vessels, arterial medial necrosis and hemorrhage, and venous thrombosis. The vascular lesions included: leukocyte adhesion to endothelial cells, transendothelial migration of leukocytes, and inflammatory cell infiltration into vessel walls. Affected vessels included arteries, terminal arterioles, capillaries, postcapillary venules, and veins. Apoptosis of endothelial and smooth muscle cells was detected in the mesenteric vasculature by both TUNEL assay and electron microscopy. Evidence of endothelial cell activation in the mesenteric arteries and veins was also observed by electron microscopy. Immunohistochemical staining detected enhanced endothelial cell expression of intercellular adhesion molecule- 1 (ICAM- 1) and von Willebrand factor (vWF) in the mesenteric arteries and veins. Mast cells were noted to be more prevalent in affected mesenteric tissue from drug-treated animals. The present findings suggest that apoptosis of endothelial and smooth muscle cells, activation of endothelial cells, recruitment of mast cells, and increased expression of adhesion molecules are important factors to the overall pathogenesis of SK&F 95654-induced vasculitis.     

Cigarette smoke induces rapid changes in gene expression in pulmonary arteries

The pathogenesis of cigarette smoke-induced pulmonary hypertension is not well characterized. We used RT-PCR to examine gene expression of nitric oxide synthase 2 (NOS-2), nitric oxide synthase 3 (NOS-3), endothelin, and vascular endothelial growth factor (VEGF) and its flk-1 receptor (VEGF-R) in main pulmonary arteries and in intraparenchymal arteries microdissected from alcohol-fixed paraffin blocks. The main pulmonary artery and intraparenchymal vessels responded in a similar fashion, with up-regulation of endothelin, VEGF, and VEGF-R gene expression evident by 2 hours after smoke exposure. Up-regulation of gene expression was still present at 24 hours after exposure, and at this time there was also a small increase in NOS-2. As a comparison, we examined the trachea and microdissected intraparenchymal airways and found up-regulation of endothelin and NOS-2 at 2 hours and additional up-regulation of NOS-3 at 24 hours. These findings suggest that the pulmonary vasculature very rapidly responds to cigarette smoke with up-regulation of mediators that control vascular cell proliferation and vascular constriction. These changes support the idea that pulmonary hypertension in cigarette smokers reflects a direct effect of smoke on the vasculature. The pattern of response in the vessels is distinctly different from that in the airways.     

Pulmonary lesions induced by 3-methylindole in mice.

The morphogenesis of pulmonary lesions and associated edema induced by the pulmonary toxicant 3-methylindole (3-MI) was studied by combined light and transmission electron microscopy. Weanling male CD-1 mice received 3-MI dissolved in corn oil by intraperitoneal injection and were studied at intervals from 2 to 360 hours after treatment. Interstitial edema was observed as early as 2 hours and was associated with focal cytoplasmic swelling and membrane alterations in both capillary endothelial cells and Type I alveolar epithelial cells and with sequestration of neutrophils. Cell swelling, cytoplasmic fragmentation, and necrosis of Type I epithelial cells was most severe at 24-48 hours after treatment. Multifocal hypertrophy and hyperplasia of Type II alveolar epithelial cells was observed at 24-96 hours after treatment. Platelet aggregation and aggregates of fibrin were frequently observed in capillaries and small arteries and veins as early as 4 hours and as late as 48 hours after treatment. In airways, the nonciliated bronchiolar epithelial (Clara) cell was the predominant cell affected. Initial lesions in nonciliated cells consisted of loss of microvilli and secretory granules followed by marked swelling of the endoplasmic reticulum and mitochondria. Necrosis of cells lining airways was most pronounced at 24-48 hours after treatment. By 144 hours after administration, pulmonary repair was complete. It is concluded that the mouse is a useful model of 3-MI-induced pulmonary injury and that damage to both Type I alveolar epithelial cells and capillary endothelial cells is important in the pathogenesis of 3-MI-induced pulmonary edema.     

Characteristics of pulmonary edema induced in rabbits of different ages

Young rabbits up to the age of 3 weeks are less resistant to chloramine (CA) than adult rabbits. The lethal dose of CA for the young rabbits was 40–50 mg/kg. They died from poisoning manifested as protracted collapse without any evidence of edema. The lethal dose of CA for older rabbits was 60–70 mg/kg. Death occurred from severe acute pulmonary edema. The young rabbits developed atypical pulmonary edema only after receiving very large doses of CA (200–250 mg/kg). Under these circumstances a small quantity of edema fluid was present and the predominant feature was hemorrahage, probably caused by the direct destructive action of CA, excreted through the lungs, on the walls of the arterioles and capillaries of the vascular system of the lungs.     

Pathology of high dose intermittent cyclophosphamide therapy

Pathologic changes induced by high dose intermittent cyclophosphamide therapy are described in 39 patients with solid tumors, lymphohematopoietic malignant disease, and bone marrow transplants. Patients receiving 50 to 120 mg. per kg. daily for one to four days showed transmural bladder injury affecting all component tissue; toxic vasculitis involving small arteries, capillaries, and venules; and interstitial, myocardial, and vascular changes in the heart. Myocardial necrosis with heart failure was the dose limiting factor of very high dose therapy. Patients receiving 15 to 30 mg. per kg. for four days showed variable degrees of bladder injury limited to the mucosa and lamina propria and vascular changes consisting only of telangiectasia. Both groups showed atypia of transitional urinary and esophageal epithelia as well as of mesenchymal cells in the lamina propria of the bladder, persistent and total ablation of spermatogenesis, and long lasting absence of ovarian follicular maturation. Bone marrow hypoplasia and lymphoid depletion developing after cyclophosphamide therapy completely disappeared an average of 3.5 weeks after the last dose.     

Ethchlorvynol-induced pulmonary edema in rats. An ultrastructural study.

Studies of ethchlorvynol (ECV)-induced pulmonary edema were undertaken for determination of the structural basis of increased microvascular permeability. Rats were administered an intravenous bolus dose of 15 mg/kg ECV and killed at time intervals between 5 minutes and 72 hours. Oyster glycogen and ferritin were used as permeability probes for identification of the sites of altered microvascular permeability. Edema fluid containing ferritin begins to accumulate in the alveolar interstitium 10 minutes after EVC . Thirty minutes after ECV, marked intersitial edema fluid is present containing both permeability probes. The absence of any appreciable transendothelial movement of either probe via vesicles and the presence of open endothelial junctions led the authors to propose the latter as the principal determinant of the increase in permeability. In addition to open endothelial junctions, prominent subendothelial blebs occur. These blebs develop in an otherwise intact endothelium and increase in frequency and size with time following their appearance at 10 minutes. Ferritin and glycogen progressively accumulate within the blebs. At 15 minutes the concentration of ferritin in blebs appears to equal that in plasma, whereas glycogen is absent or sparsely present in a few blebs. At 60 minutes both permeability probes have become concentrated in the blebs. The mechanism of formation of the blebs and concentration in them of the permeability probes cannot yet be specified. The lesion caused by ECV is completely reversible, so that by 72 hours after ECV there is complete resolution of interstitial edema, disappearance of the subendothelial blebs, and closure of endothelial junctions. A small amount of exudate remaining in the alveoli is cleared by 72 hours.     

老年患者骨水泥型人工髋关节置换前后的凝血功能

背景：由于老年患者自身的高凝倾向,骨水泥型人工髋关节置换后更容易发生深静脉栓塞、弥漫性血管内凝血、肺栓塞、脑栓塞等并发症。 目的：观察老年患者骨水泥型人工髋关节置换前后凝血4项凝血酶原时间、活化部分凝血活酶时间、凝血酶时间和纤维蛋白原的变化。 方法：检测40例人工髋关节置换老年患者骨水泥植入前10 min,植入后30 min、1 h、2 h、3 h 凝血酶原时间、活化部分凝血活酶时间、凝血酶时间和纤维蛋白原各项指标。 结果与结论：与植入前10 min比较,植入后30 min凝血酶原时间明显下降(P < 0.05),纤维蛋白原明显升高(P < 0.05),植入后3 h均恢复到植入前状态(P > 0.05)。活化部分凝血活酶时间、凝血酶时间在骨水泥植入前后变化均不明显(P > 0.05)。结果表明患者在骨水泥植入后短时间内会出现高凝血状态,在植入3 h后基本消除,提示在植入骨水泥后的3 h是监测凝血的重要时间段。     

牛心包补片修补心脏缺损并雾化吸入伊洛前列环素降低肺动脉高压

背景：对于先天性心脏病合并肺动脉高压的治疗,传统降低肺动脉高压的药物效果确实,但存在不易监测、停药后反跳等现象;传统的心脏涤纶补片较易引起吻合口变形、血栓、栓塞、溶血和感染等并发症。 目的：观察应用戊二醛处理牛心包补片和雾化吸入伊洛前列环素治疗先天性心脏病合并肺动脉高压的效果。 方法：选择90例先天性心脏病合并肺动脉高压患者,术中采用戊二醛处理的牛心包补片修补心脏间隔缺损,术后雾化吸入伊洛前列环素30 ng/(min•kg),日间12 h按1次/4 h给药,夜间12 h按1次/6 h给药,连续给药2 d。记录每次吸入药物前、吸入后即刻、吸入30 min后平均动脉压、平均肺动脉压、体循环阻力指数与肺循环阻力指数,于随访期观察有无心包材料相关并发症和心功能情况。 结果与结论：90例患者复查超声心动图见活瓣均已关闭,无分流,心脏间隔缺损无回声中断,心脏收缩功能正常,未发现与牛心包补片相关的不良反应。所有患者不同时间点平均动脉压、体循环阻力指数比较差异无显著性意义。患者吸入药物后即刻平均肺动脉压、肺循环阻力指数明显低于吸入药物前(P < 0.01),吸入30 min后平均肺动脉压、肺循环阻力指数亦明显低于吸入药物前(P < 0.05)。表明应用戊二醛处理的牛心包补片和雾化吸入伊洛前列环素治疗先天性心脏病合并肺动脉高压安全、有效。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

Lung microvascular permeability to dextran in alpha-naphthylthiourea-induced edema. Sites of filtration, patterns of accumulation, and effects of fixation.

The detailed topography of filtration and of accumulation of the tracer dextran 75 was studied in 3 control dogs and in 9 experimental dogs in which edema was induced with 27 mg/kg alpha-naphthylthiourea. When moderately severe edema was present, 15-20 ml/kg of 6% dextran 75 was infused over 10-15 minutes; lung lobes were then fixed immediately by immersion, airway instillation, or vascular perfusion with 5% glutaraldehyde, 3% paraformaldehyde, or by freeze-substitution. For light microscopy, sections were embedded in methacrylate and stained with periodic acid-Schiff; for electron microscopy, they were embedded in Epon. The tracer was confined to the vasculature in controls. In all but one animal with edema, the tracer was seen in relation to capillaries, nonmuscular and partly muscular arteries, and veins, not in the walls of muscular arteries or around bronchial vessels. The dextran rapidly entered alveoli, lymphatics, and the interstitium around small vessels; there was much less tracer in the interstitium around larger vessels and essentially none around airways, consistent with the notion the interstitium acts as a sequestered pool. Furthermore, it was found that significant artifacts resulted from airway instillation and vascular perfusion fixation.     

Pulmonary hypertension due to tumor emboli: A report of three autopsy cases with morphological correlations to radiological findings

Three cases of pulmonary hypertension caused by tumor emboli to the lungs are described. Two of the three cases had a clinical diagnosis of pulmonary thromboembolism until surgical embolectomy, and the other had a diagnosis of primary pulmonary hypertension. Autopsy disclosed chondrosarcoma, choriocarcinoma and gastric cancer as the primary tumors, respectively. Pulmonary vascular obstruction due to tumor embolism leading to pulmonary hypertension is a previously rare clinical entity, and obstructed pulmonary vessels are believed to tend to be small vessels. We compared the autopsy and radiological findings and concluded that pulmonary tumor embolism involved not only the small peripheral arteries but also the segmental and/or lobar arteries.     

Functional and fine structural changes in isolated rat lungs challenged with endotoxin ex vivo and in vitro.

The aim of this study was to relate changes in rat lung functions caused by the endotoxin lipopolysaccharide (LPS) to alterations in structure. The following four experimental groups were used: 1), control in vitro, perfusion for 150 minutes; 2), LPS in vitro, perfusion for 150 minutes and infusion of 5 mg of LPS after 40 minutes; 3), control ex vivo, perfusion for 10 minutes; and 4), LPS ex vivo, lungs perfused for 10 minutes from rats treated for 110 minutes with 20 mg/kg LPS intraperitoneally. Histologically, blood-derived leukocytes were detectable only in lungs from group 4, where neutrophils were found in capillaries, interstitium, and endothelial pouches. LPS treatment increased pulmonary resistance and decreased pulmonary compliance in group 4 (ex vivo), and, to a greater extent, in group 2 (in vitro). In these two groups, formation of giant lamellar bodies in the type II pneumocytes was observed. By histological examination, the bronchoconstriction induced by LPS in vitro was localized to the terminal bronchioles. At 2 hours after LPS treatment, no edema and no change in precapillary and postcapillary resistance, capillary pressure, vascular compliance, capillary permeability, and the wet/dry ratio was observed. Thus, our major findings are that LPS induced constriction of the terminal bronchioles in vitro, formation of giant lamellar bodies in type II pneumocytes ex vivo and in vitro, and trapping of neutrophils in endothelial pouches in vivo.     

Identification of vascular progenitor cells in pulmonary arteries of patients with chronic obstructive pulmonary disease

Progenitor cells of bone marrow origin migrate to injured vessels, where they may contribute to endothelial maintenance and vessel remodeling through vascular endothelial growth factor (VEGF)-related signals. To what extent progenitor cells may play a role in vascular changes occurring in patients with chronic obstructive pulmonary disease (COPD) remains undetermined. In this study we sought to identify vascular progenitor cells in pulmonary arteries of patients with COPD and to investigate whether the presence of these cells could be related to changes in endothelial function or the expression of VEGF. Pulmonary arteries of nine patients with COPD and six control subjects were studied. Scanning electron microscopy demonstrated areas of denuded endothelium in the arteries of patients with COPD. Vascular progenitor cells were identified by immunohistochemistry and immunogold using antibodies against AC133, CD34, and CD45. AC133+ cells were localized in the endothelial surface, close to denuded areas. The number of AC133+ and CD45+ cells in pulmonary arteries was greater in patients with COPD than in control subjects. The number of AC133+ cells correlated with the response of pulmonary artery rings to hypoxic stimulus. AC133+ and CD45+ cells were also identified in the intimal layer. The wall thickness correlated with the number of progenitor cells in the intima and with VEGF and VEGF receptor-2 mRNA expression. We conclude that patients with COPD show an increased number of bone marrow-derived progenitor cells in pulmonary arteries. These cells seem to contribute to ongoing endothelial repair, but they might also be involved in the pathogenesis of pulmonary vascular remodeling.     

Allogeneic bone marrow transplantation in an osteopetrosis patient: first report in Thailand

We described the successful allogeneic matched sibling bone marrow transplantation (BMT) in a 5-year-old Thai boy in whom osteopetrosis was diagnosed on the basis of anemia, thrombocytopenia, leukoerythroblastosis, sclerotic bone, hepatosplenomegaly, and visual deficit from an encroachment of cranial nerve foramina. The preparative regimen included 4 days of busulfan 4 mg/kg/day, and 4 days of cyclophosphamide 50 mg/kg/day. Complete hematopoietic engraftment and no evidence of graft versus host disease were shown after BMT. Complete hematologic findings were corrected. His hematopoietic chimerism was changed to that of his donor. Post BMT, he has no hepatosplenomegaly. His bone radiographic findings revealed normal after BMT. Bone marrow biopsy showed normalized bone and bone marrow matrix. However, his vision remained impaired. We believe that this is the first case of successful bone marrow transplantation in an osteopetrosis patient in Thailand.     

Rabbit bone marrow after administration of saponin. An electron microscopic study

Saponin rapidly induced injury to the wall of vascular sinuses in rabbit bone marrow so that the barrier between hematopoietic cells and the circulation became defective. This change was followed by hypocellularity and necrosis and fibrosis. Adult male rabbits received saponin intravenously (2 mg. per kg.) every 4 days for periods of up to 4 weeks; the animals were killed at varied times. In untreated animals, much of the sinus wall consisted only of endothelium. Within 2 hours after administration of saponin the endothelium was damaged and hematopoietic cells, mostly reticulocytes and normoblasts, entered the circulation. Some sinuses hemorrhaged into the hematopoietic compartment. At 4 hours, sinuses were markedly dilated and hemorrhage was extensive. By 3 days, extravasated erythrocytes, which were tending to aggregate, were unevenly distributed in the extravascular space of marrow. Damaged hematopoietic cells were dispersed among them. Regenerating blood vessels were noted and a few clusters of hematopoietic cells occurred in association with fibroblasts. At 1 week, a large portion of the marrow was either necrotic or contained large-scale diffuse or focal hemorrhage. Fibrotic areas often surrounded the arteries. After 2 to 4 weeks, myelofibrosis became pronounced. The fibrotic tissue was well vascularized and contained small clusters of hematopoietic cells and a few fat cells. Macrophages were abundant and tended to fuse, forming multinucleated giant cells surrounding pockets of degenerated fat cells.     

Anatomic pathway of pulmonary fluid leakage in endotoxemia induced in rats. The red blood cell packing method and its application.

The anatomic site of pulmonary fluid leakage in endotoxemia in rats was investigated using the red blood cell packing method and low-dose horseradish peroxidase as a tracer. To differentiate between arterioles and venules in a given section by light and electron microscopy, human red blood cells fixed with 4% paraformaldehyde were administered to the rat pulmonary arterial trunk at a pressure of 40 cm water. Fixed red blood cells were packed in the lumina of arteries, arterioles, and a few capillaries surrounding arterioles, while veins, venules, and almost all capillaries were void of red blood cells in the lumina. Fifteen minutes after the intravenous administration of 3 and 30 mg/kg of Escherichia coli endotoxin, extravascular leakage of horseradish peroxidase from venules (nonmuscular veins) was evident. Two hours after the intravenous injection of the same doses of endotoxin, some arterioles (nonmuscular arteries) and venules (non-muscular veins) showed extravascular leakage of horseradish peroxidase, while few capillaries showed this leakage. These results suggest that pulmonary fluid leakage occurs predominantly through venules in the early phase of endotoxemia (at 15 minutes), while the arterioles contribute to fluid leakage in addition to venules in the late phase of endotoxemia (at 2 hours).