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At least 19 recordsLinked to original sources
PubMed1997

Vascular endothelial growth factor is the major angiogenic factor in omentum: mechanism of the omentum-mediated angiogenesis.

Omentum has been used clinically to promote wound healing and to stimulate the revascularization of ischemic tissues. The biologic mechanism responsible for these effects has, however, not yet been defined. A number of polypeptide growth factors that possess potent angiogenic properties have recently been identified, and we therefore sought to determine whether one of these growth factors might be responsible for the angiogenic properties of the omentum. The levels of vascular endothelial growth factor (VEGF) protein in a number of rat tissues and organs were analyzed by Western and enzyme immunoassay analysis. Because omentum was found to have the greatest VEGF concentrations of the tissues examined, antibody neutralization, transcription inhibition assays, and Northern blot analysis were performed under hypoxic and normoxic conditions on tissues extractions and primary tissue cultures of omentum to further characterize the functional significance of VEGF expression in these tissues. The omentum demonstrated the highest VEGF secretion rate as well as the highest concentration of VEGF protein of the various rat tissues and organs examined. Fractionation studies of the omentum furthermore demonstrated that omental adipocytes, rather than the stromal-vascular cells, were the primary source of VEGF protein. An endothelial cell mitogenic assay showed that a major portion of the mitogenic activity of heparin-binding proteins and conditioned media derived from omentum was abolished by VEGF antibody. Additional studies with the transcription inhibitor actinomycin-D furthermore demonstrated that the VEGF gene was continuously transcribed in the rat omental adipocytes. Incubation of the omental adipocytes under hypoxic conditions induced approximately a 1.7-fold increase in VEGF protein expression, which was abolished by actinomycin-D. Northern blot analysis demonstrated that hypoxia resulted in upregulation of the VEGF mRNA in the hypoxia-cultured omental adipocytes, suggesting that the augmentation of VEGF expression in omental adipocytes by hypoxia occurs at the transcriptional level. These data suggest that VEGF is the major angiogenic factor produced by omentum and possibly underlies the mechanism of omentum-induced angiogenesis. Augmented expression of VEGF by omental cells under hypoxic conditions may furthermore reflect the mechanism responsible for enhancing the angiogenic activity of omentum in the setting of ischemia.

Adipose Tissue↗
PubMed1978

[A new use for the freely transplanted omentum. Management of a late radiation injury of the brachial plexus using freely transplanted omentum and neurolysis].

A short review of the structural characteristics and the function of the greater omentum is presented. The results of treatment of secondary lymphedema by free transplantation of the omentum with microvascular anastomoses in the canine model and their relevance for clinical application are discussed. Clinical indications, operative technique, and results of omental transplantation and exoneurolysis of the brachial plexus in seven patients with constrictive, radiation induced brachial plexus paralysis, with and without secondary lymphedema, are reviewed. No effect of the grafted omentum on arm-lymphedema was observed over the entire observation period of 1 1/2--4 years. Minor degree reversion of neurodegenerative changes was found in two patients, in all other patients, these changes stopped. The most impressing result was the immediate and permanent disappearance of pain in all patients.

Adult↗
PubMed1996

[A case report of a left bronchial stump fistula from which the wrapped omentum was removed, because of rupture of the anastomotic aneurysm of the descending thoracic aorta--functions of the wrapped omentum in the early phase and extended phase after surgery].

The omental wrapping is a method of the choice for empyema with bronchopleural fistula. A 71-year-old woman, who had undergone graft replacement for the aneurysm of the descending thoracic aorta, underwent left pneumonectomy for lung abscess. Two months after surgery, the bronchopleural fistula in the stump was presented and successfully repaired by omentopexy. When anastomotic aneurysm rupture of the graft was presented one year later, the management was successful because mortal bleeding was prevented by the omental pedicle flap in the left thoracic cavity. Though we removed the omental flap with hematoma, the fistula didn't recurred. The omentum facilitates the healing of bronchopleural fistula in the early phase after surgery, but the healing course in the extended phase had not have any trouble without omental vascularization.

Aged↗
PubMed1992

The fetal omentum in mice and humans. A site enriched for precursors of CD5 B cells early in development.

From these studies the fetal omentum appears to be an important site of B-cell generation in humans and a source of CD5 B cells in mice. We have analyzed the fetal omentum in other species and have found that B-cell development as determined by the presence of cytoplasmic IgM+ pre-B cells is also detected in the fetal rabbit omentum. We do not know if there is bias towards the production of CD5 B cells in this species; however, these preliminary results demonstrate that this site may be conserved throughout evolution in mammals as a site of B-cell generation. Because the fetal liver is also a source of precursors that can reconstitute this B-cell subset, what is the relationship between omentum and liver during the development of Ly-1 B cells? The most obvious relationship between these two sites is that cells simply migrate from one location to the other; that is, precursor cells may migrate from the fetal liver into the fetal omentum and in this milieu give rise to exclusively Ly-1+ B cells or the sister population. Alternatively, precursors of Ly-1 B cells may arise in the omentum and migrate to the liver. This is demonstrated graphically in the diagram (Fig. 6a) of a transverse section through an 8-week human fetus. In this paper, however, we suggest a model for the development of Ly-1+ B cells from the omentum and liver in which Ly-1 B cells arise from distinct precursors located in situ in the mesodermally derived omentum and mesothelial-derived liver capsule. The omentum primordia forms as the back to back fusion of the mesodermally derived lining of the peritoneal cavity, and this lining surrounds the developing gut when the liver begins to develop as an outgrowth of the intestinal primordia at approximately 3.5 weeks gestation; the outer covering or capsule of the liver is derived from the same tissue of origin as the omentum. Figure 6B is a diagram of a section through the same plane as Figure 6A but the body wall has been omitted. We propose that the Ly-1+ B cells arise in situ in the omentum and lining of the liver as indicated in Figure 6B. That Ly-1+ B cells arise from distinct precursors has been suggested by others, but ours is the first evidence for a developmental site that apparently contains B-cell progenitors for this B-cell subset.

Animals↗
PubMed1995

[Transposition of the omentum to the thigh, for the vascular salvage of a limb. Apropos of 17 cases].

A new procedure to supply effective anastomotic blood supply via the omentum transpositioned to the hip in cases of impaired lower limb vascularization was proposed in 16 cases of stage III and stage IV obliterative artherosclerosis including one case of massive venous thrombosis. The results demonstrated that under rigorously controlled fundamental conditions, circulation can be established and the limb can be saved. 1--good omentum vascularization is essential: the two gastroepiploic arteries must have a large caliber and form a complete anastomotic circle. 2--After disconnecting the omentum from the stomach, while carefully protecting the gastro-epiploic arcade, one pedicle is sectioned and the other is saved depending upon the side the omentum is transpositioned. It is best to save the right pedicle which has a stronger flow even for the left limb. If the omentum is ample enough, the anatomic situation does not require a lengthening plasy. 3--If the omentum is insufficiently long, it is lengthened by a second counter-section between the two gastro-epiploic and epiploic arcades. The ends of the arcades can thus be placed in direct contact forming a unique continuous arcade. This plasty is only possible if the anastomotic circle of the gastro-epiploic arcade is complete. 4--Transposition to the hip is made by including the omentum between the rectus and its posterior sheath through a newly formed channel widening the crural canal. The omentum is thus incorporated as a bridge forming a major circulatory route between the subclavian artery and the pelvic and lower limb arteries. 5--We recommend transpositioning the omentum after lumbar sympathectomy to favour strong vasodilatation and lower flow resistance helping create favourable conditions for the new anastomotic circulation. 6--Based on these specific conditions, we have had excellent results in 80% of the cases for the entire life-span of the patients who underwent the operation. The two cases with poor results occurred after a major technical error due to a lengthening plasty on an omentum without a complete gastro-epiploic arcade.

Aged↗
PubMed1992

The human fetal omentum: a site of B cell generation.

The fetal mouse omentum has been shown to be a source of precursors that exclusively reconstitutes Ly1+ B cells and the closely related Ly1- sister population, but not conventional B cells or T cells. We have extended these studies to compare B cell development in the human fetal omentum, liver, and spleen, and to demonstrate that the pro/pre-B cell compartment (CD24+, sIgM-) is detected in the omentum and liver but not spleen as early as 8 wk of gestation. From 8 to 12 wk of gestation, the proportions of IgM+ cells that were pre-B cells (cIgM+/sIgM-) in the omentum and liver were 53 +/- 15% and 45 +/- 13%, respectively, and IgM+ cells were not detectable in the spleen. After 12 wk, the percentage of pre-B cells was unchanged in the fetal liver (41 +/- 10%) but decreased significantly in the omentum (25 +/- 14%); pre-B cells were now detected in the spleen but at much lower percentages (2 +/- 3%) than either the omentum or liver. The nuclear enzyme, Tdt, was detected in approximately 25% of the CD24+ cells in the omentum and liver during the 8-12-wk time period, however, Tdt+ cells were not detected in the spleen. Approximately 40% of the mature B cells found in the omentum and spleen were CD5+ compared with only 20% in the liver. These results demonstrate that the fetal omentum, like the fetal liver and bone marrow, is a primary site of B cell development.

Antibodies, Monoclonal↗
PubMed1995

[Activation of the major omentum-associated lymphoid tissue in Crohn disease].

The mucosa associated lymphoid tissues of the intestinal lamina propria or the bronchial mucosa, respectively, represent a separated and well defined immunologic compartment. Due to highly specialized functions, subpopulations of lymphoid cells are distributed unevenly between the compartments and unique regulatory mechanisms developed to sustain integrity of mucosal surfaces. With this study we investigate whether an omentum associated lymphoid tissue exists and whether it partakes in immunologic processes involved in the perpetuative intestinal inflammation in Crohn's disease. Mononuclear cells from surgically resected omentum tissue (10 patients with Crohn's disease, 10 patients with malignomas or inflammatory control diseases (diverticulitis)) were isolated by collagenase digestion and subsequent serial density centrifugation. Phenotypic analysis was carried out by immunofluorescent labeling with a panel of monoclonal antibodies as well as peanut agglutinin. Most interestingly, the percentage of CD4-T(Helper) cells among omentum mononuclear cells was decreased in comparison with peripheral blood mononuclear cells, whereas the percentage of monocytes/macrophages and of natural killer cells appeared to be increased. In comparison with normal peripheral blood a higher percentage of normal omentum mononuclear cells were activated. It thus appears that a defined immunologic compartment exists which is different in its cellular composition from peripheral blood as well as from intestinal mucosa associated lymphoid tissue and which may be called omentum associated lymphoid tissue. In Crohn's disease subpopulations of omentum mononuclear cells did not change in number, however immunologic activation increased further and appears to be highly increased in comparison to both omentum cells from disease specificity controls (diverticulitis) and Crohn's disease peripheral blood cells. We conclude that omentum associated lymphoid tissue may be described as an unique immunologic compartment which may play a role in activating events in chronic intestinal inflammation in Crohn's disease. Further studies will address functional characteristics of the omentum associated lymphoid tissue and will investigate regulatory mechanisms which may contribute to the inflammatory process in Crohn's disease.

Adult↗
PubMed1989

Use of the omentum in chest-wall reconstruction.

Increased use of the omentum in chest-wall reconstruction has paralleled the refinement of anatomic knowledge and the development of safe mobilization techniques. Important anatomic points are the omental attachments to surrounding structures, the major blood supply from the left and right gastroepiploic vessels, and the collateral circulation via the gastroepiploic arch and Barkow's marginal artery. Mobilization of the omentum to the thorax involves division of its attachments to the transverse colon and separation from the greater curvature to fabricate a bipedicled flap. Most anterior chest wounds and virtually all mediastinal wounds can be covered with the omentum based on both sets of gastroepiploic vessels. The arc of transposition is increased when the omentum is based on a single pedicle, allowing coverage of virtually all chest-wall defects. The final method of increasing flap length involves division of the gastroepiploic arch and reliance on Barkow's marginal artery as collateral circulation to maintain flap viability. With regard to chest-wall reconstruction, we have included the omentum in the armamentarium of flaps used to cover mediastinal wounds. The omentum is our flap of choice for the reconstruction of most radiation injuries of the chest wall. The omentum may also be used to provide protection to visceral anastomoses, vascular conduits, and damaged structures in the chest, as well as to cover defects secondary to tumor excision or trauma. In brief, the omentum has proved to be a most dependable and versatile flap, particularly applicable to chest-wall reconstruction.

Humans↗
PubMed2003

Omentum is highly effective in the management of complex cardiothoracic surgical problems.

OBJECTIVES: Vascularized, pedicled tissue flaps are often used for cardiothoracic surgical problems complicated by factors that adversely affect healing, such as previous irradiation, established infection, or steroid use. We reviewed our experience with use of the omentum in these situations to provide a yardstick against which results with other vascularized flaps (specifically muscle flaps) could be compared. METHODS: A retrospective review was undertaken of 85 consecutive patients in whom omentum was used in the chest. In 47 patients (group I), use of omentum was prophylactic to aid in the healing of closures or anastomoses considered to be at high risk for failure. In 32 patients (group II), omentum was used in the treatment of problems complicated by established infection. In 6 patients (group III), omentum was used for coverage of prosthetic chest wall replacements after extensive chest wall resection. RESULTS: Overall, omental transposition was successful in its prophylactic or therapeutic purpose in 88% of these difficult cases (75/85). Success with omentum was achieved for 89% of patients (42/47) in group I, 91% of patients (29/32) in group II, and 67% of patients (4/6) in group III. Three patients (3.5%) had complications of omental mobilization. Four patients (4.7%) died after the operation as a result of failure of the omentum to manage the problem for which it was used. CONCLUSIONS: Results with omental transposition compare favorably with published series of similarly challenging cases managed with muscle transposition. Complications of omental mobilization are rare. We believe that its unique properties render the omentum an excellent choice of vascularized pedicle in the management of the most complex cardiothoracic surgical problems.

Cardiac Surgical Procedures↗
PubMed1994

Evaluation of the greater omentum in the treatment of experimental lymphedema.

Despite advances in microsurgery, the most suitable operation for primary lymphedema remains unclear. A variety of tissue transplants and artificial substances have been used to facilitate drainage of peripheral lymph. The greater omentum, for example, has absorptive lymph draining capability, fights infection, and is expendable for the abdomen. Previous attempts to use the omentum in treatment of clinical lymphedema have, however, been disappointing. This discrepancy between theory and outcome prompted us to reevaluate the role of the omentum in the treatment of chronic lymphedema. In rabbits, mobilization of omentum was carefully examined by three separate techniques and the presence of natural lymph nodal-venous (L-V) shunts determined by an injection of Evans blue into the omentum with sampling later of plasma from the gastroepiploic venous blood. In dogs after promotion of unilateral chronic hindlimb lymphedema by soft tissue excision and sclerosis, the results of four methods of omental transplantation with or without L-V shunt for relief of lymphedema were compared. The results in rabbits suggest that although the greater omentum can be lengthened without jeopardizing its blood supply, it is inappropriate to lengthen it based on blood vascular arcades alone because the omental lymphatics do not strictly follow these arcades in the more distal portion, and with elongation, may be interrupted even though the blood supply remains intact. Moreover, because there is no natural L-V shunt within the greater omentum, the addition of a L-V shunt in dogs in addition to omental transplantation seems to increase effectiveness of the omentum for draining hindlimb lymph after its autotransplantation.

Animals↗
PubMed1994

Omentum and basic fibroblast growth factor in healing of chronic gastric ulcerations in rats.

Omentum was shown to exhibit angiogenic activity, but its role in healing of chronic gastric ulcers is unknown. This study was designed to compare the effects of omentum and basic fibroblast growth factor (bFGF), a potent angiogenic factor, on healing of chronic gastric ulcers in rats. Several series of rats with gastric ulcers were used: series A with intact omentum (control), series B with omentum resected, and series C with omentum placed on the serosal side of the ulcer. Series A-C were divided into four groups treated with vehicle (I); indomethacin (II), an inhibitor of prostaglandin formation, difluoromethylornithine (DFMO) (III); an inhibitor of polyamine biosynthesis or bFGF (IV). Seven days after ulcer induction, the animals were anesthetized, the gastric blood flow (GBF) was determined by laser Doppler flowmetry (LDF), and the ulcer area was measured by planimetry. Biopsy samples of the ulcer margin were taken for determination of the number of capillaries and myofibroblasts in the granulation tissue. Attachment of omentum significantly accelerated ulcer healing, whereas omentectomy delayed this process. LDF revealed the decrease in the GBF at the ulcer margin to 45% and at the ulcer bed to 18% of the value recorded in the intact adjacent mucosa. Attachment of the omentum significantly increased the blood flow at the ulcer margin and increased the number of capillaries and myofibroblasts in the granulation tissue. Indomethacin (1 mg/kg/day) that inhibited mucosal PGE2 by about 85% delayed significantly ulcer healing without affecting the blood flow in the ulcer area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Ultrasound-assisted lipolysis of the omentum in dwarf pigs.

Successful surgical treatment of medium degree obesity by subcutaneous liposuction has been reported in the literature. In obesity, most adipose tissue is visceral, mainly omental, and the resection of omentum is a mutilating procedure for the intestinal tract. Because of this, we planned to reduce omental adipose tissue by an apparently conservative approach: ultrasound-assisted lipolysis. The purpose of this study was to assess the feasibility and safety of this procedure in an animal experimental model, drawing clinical and autoptic patterns. We chose pigs because they are functionally analogous to humans, although they store less fat in the omentum, whose structure looks like a veil. Four male dwarf pigs were fed, since weaning, with hyperlipidic fodder. When they were eight months old, they were operated on under general anesthesia in our laboratory for experimental surgery. After laparotomy, the omentum was delivered and treated with ultrasound for 1 hour. Before and just after the sonication, biopsies were drawn from omentum and processed for histologic findings. After 50 days, the surviving animals were sacrificed and autopsied; specimens from omentum, liver, and spleen were histologically processed. Two animals died during the operation, while the two surviving animals were in good general condition. Macro and microscopic observations demonstrated that the ultrasound can liquefy omental fat, sparing its fibrous network in the immediate time; during the postoperative period, an intense inflammatory reaction developed; macroscopic observation evidenced fibrous adhesions of the omentum to the surrounding organs; the connective tissue network was thickened and the whole omentum was twisted on itself. The high mortality rate could be due either to the surgical learning curve or to casualty or to lethal effects of ultrasound on the cardiac conductive system; the inflammatory peritoneal reaction could be specifically due to ultrasound or to surgical handling.

Animals↗
PubMed1990

Identification of endothelial and mesothelial cells in human omental tissue and in omentum-derived cultured cells by specific cell markers.

Human omental tissue has been used as a source for the isolation and cultivation of microvascular endothelial cells, but also for mesothelial cells. Since both cell types have several morphologic and functional features in common, concerns were raised whether endothelial cells can be separated from mesothelial cells by the methods described for the isolation of microvascular endothelial cells. In the present study, endothelial cells were identified in the capillaries of native human omentum by several endothelial-cell specific markers. von Willebrand factor was demonstrated by polyclonal and monoclonal antibodies, a lectin-specific ligand by Ulex europaeus I, and an endothelial-cell specific surface epitope by the monoclonal antibody, PAL-E. These markers were not found positive with mesothelial cells of native omentum. Mesothelial cells were identified by monoclonal antibodies against the intermediate filaments, cytokeratin and vimentin. After having demonstrated the specificity of the methods for the distinction between endothelial and mesothelial cells within native omentum, these methods were applied to omentum-derived cells previously claimed to be microvascular endothelial cells. These cultured cells proved to be negative for von Willebrand factor, Ulex europaeus I ligand and PAL-E epitope. In contrast to this, the cultivated cells stained positive to cytokeratin and vimentin. Furthermore, it was shown by immunoprecipitation studies that omentum-derived cells did not synthesize and secrete vWF, indicating the nonendothelial nature of these cells. Finally, electron microscopy demonstrated microvilli on the surface of cultivated omentum-derived cells indicative for the mesothelial origin of these cells. The data presented demonstrate that the cells obtained using the previously published methods for the isolation and cultivation of "microvascular endothelial cells" from omental tissue are of mesothelial and not of endothelial origin. Thus, a great number of data obtained with this type of omentum-derived cells thought to be microvascular endothelial cells need re-evaluation.

Antibodies, Monoclonal↗
PubMed1989

[What does the omentum plug accomplish in colorectal tumor surgery? A 10-year follow-up].

In 23 of 47 patients who underwent surgery for malignant colorectal tumors between January 1978 and December 1986, the residual cavity was treated with a pedicled omental plug after radical resection of the tumor-bearing areas. There was advanced transmural tumor spread in 13 omentum patients and in 9 operated without using omentum. The other patients had equally distributed T2 and T3 stage tumors. Complications were similar in both groups, but perineal infection was slightly less frequent and less significant in the omentum group. Hospitalization was 23 days in patients with the omental plug and 34 days in the others. Life quality, as shown by the activity index, was better in the omentum group. 30-day postoperative mortality was 8.5% in both groups. Individual survival after surgery was 23 months with the omental plug, compared with 15 months in patients without this procedure. At 5 years, however, survival rate was similar. Postmortem revealed no tumor spread alongside the transposed omentum, which had changed to a mesentery-like structure. From these results it is clear that the omentum plug does not achieve cure in carcinoma or longterm survival, but improves the complication rate and individual survival time. We can therefore recommend this procedure as palliative treatment, since even extensive defects can be covered effectively by omentum.

Adult↗