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Background: Interpretation of intravital microscopic observations is complicated by the "inflammatory"-type response to the trauma inflicted on the tissue by the surgical preparation. The present study evaluates different experimental conditions for prolonged observations of the mesenteric microcirculation in the rat., Methods: The mesentery was exteriorized through a median laparotomy and subjected to an organ bath or a modified plastic foil technique. Hemodynamic, metabolic, respiratory, and microcirculatory data were analyzed., Results: In contrast to the plastic foil technique, which yielded stable baseline values over a 5-h observation period, venular velocity and wall shear rates decreased significantly in the organ bath technique, and leukocyte adhesion to the endothelium was significantly increased. Likewise, abdominal blood flow decreased significantly by 35% and base excess declined (-10.0+/-0.4 mmol/L) in the organ bath, with reduced pco(2) (26.4+/-2.5 mm Hg vs. 33.7+/-1.1 mm Hg in plastic foil technique) due to respiratory pH compensation., Conclusions: The plastic foil technique was found clearly superior to the organ bath technique for maintenance of stable baseline metabolic, hemodynamic, and microcirculatory conditions in mesenteric intravital microscopy., (Copyright 2000 Academic Press.)

Leukocyte adhesion and emigration are involved in host defense and phagocytosis and thus serve a beneficial role during the mounting of a well-contained inflammatory response. However, in certain situations, leukocytes may turn against the host and contribute to tissue damage and organ dysfunction. While trying to summarize the current opinion about the mechanisms by which leukocytes contribute to tissue damage, one finds that leukocyte-inflicted tissue damage involves a network of marked complexity, requiring an orchestrated crosstalk between different cell types, mediators, cytotoxic agents, and their respective inhibitors. Now that an abundance of information is available as to where, when, and how leukocytes contribute to tissue damage, one of the key questions remains unsolved: is leukocyte-inflicted tissue damage true damage, or is it rather a crucial step in tissue repair, healing, and scar formation? Future research will have to address this question, thoroughly differentiating between the role of leukocytes in diverse pathophysiological situations, ranging from cigarette smoke-induced pulmonary emphysema and immune-triggered transplant rejection to myocardial and cerebral infarction. Knowledge of how leukocytes damage tissue only shows us the tools; knowledge of why will provide us with the basis for effective therapeutic interventions.

CB1 and TRPV1 receptors modulate enteric neurotransmission and colonic inflammation. This study investigates early electrophysiological changes in distal colon of wild-type and receptor deficient mice after an inflammatory insult set by dinitrobenzene sulfonic acid (DNBS). Colitis was induced by DNBS in CB1−/− mice, TRPV1−/− mice, and their respective wild-type littermates. Electrophysiological properties consisting of membrane potentials and electrically induced inhibitory junction potentials (IJP) of circular smooth muscle cells were evaluated at different time points. Additionally a histological colitis severity score was evaluated in CB1+/+ and CB1−/− mice 24 h after DNBS. Inflammation caused spontaneous atropine insensitive rhythmic action potentials in CB1−/− and TRPV1−/− mice but not in wild-type animals. This indicates that membrane stability is disturbed, which in turn indicates a lack of protective mechanisms. Focal electrical neuronal stimulation of the myenteric plexus induced IJP in the smooth muscle cells. Twenty-four hours after initiation of inflammation, the duration of the IJP is prolonged in all animals, indicating disturbances within neuromuscular interaction. In CB1−/− mice, it is interesting that the duration of IJP was significantly extended, as compared to CB1+/+ mice pointing toward missing protective mechanisms in the CB1−/− mice. Inflammatory insults in the mouse colon induce reproducible changes in the electrophysiological properties and such changes correlate with duration of colitis. In mutants, these electrophysiological changes display different patterns, suggesting the lack of protective properties for neuromuscular interactions and membrane stability. [ABSTRACT FROM AUTHOR]

The role of leptin in the immune system has been well established. While adipocytes represent the major source, leptin production by lymphocytes, infiltrating at the site of inflammation, was recently demonstrated. However, the significance of this locally released leptin remains unresolved. In the present study, two models in which absence of leptin-signalling is associated with protection were employed: the model of ConA-induced hepatitis and the CD4+CD45Rbhigh transfer model of colitis. For the ConA model, scid mice were reconstituted with either WT or leptin-deficient ( ob/ob) CD4+ T cells. Eight weeks post transfer, ConA was injected and serum ALT, TNFα, leptin as well as liver mononuclear cell activation and histological signs of inflammation were evaluated. No difference between recipients of WT or ob/ob cells was observed for any of the parameters evaluated. In the second model, either WT or ob/ob CD4+CD45Rbhigh cells were transferred into scid mice. No histological differences were detected, although recipients of ob/ob cells showed higher weight loss compared to recipients of WT cells. Spontaneous production of IL-6 from colon cultures obtained from recipients of ob/ob cells was reduced compared to recipients of WT cells, whereas stimulation of lamina propria lymphocytes with leptin resulted in a higher IFNγ release in recipients of ob/ob cells compared to recipients of WT cells. In conclusion, the present study provides evidence that T cell-derived leptin does not play a major role in the regulation of the inflammatory process, indicating that the adipose tissue is the critical player in the immune-modulating effects of leptin. [ABSTRACT FROM AUTHOR]

Background: Leptin regulates appetite through the long isoform of its receptor in the hypothalamus. Although leptin regulates immune responses, it is still unknown whether a direct effect of leptin on lymphocytes is required. Aims: To clarify whether expression of leptin receptors on I lymphocytes modulates intestinal inflammation in mice. Methods: The model of colitis induced by transfer of CD4+CD45RBhigh (RBhigh) cells into scid mice was used. Wild-type (WT) or leptin receptor deficient (db/db) RBhigh cells were transferred into scid mice and development of colitis evaluated. Results: Leptin receptors were expressed on both RBhigh and RBhigh cells. Intestinal lymphocytes of mice with colitis expressed high leptin levels compared with healthy controls whereas the opposite was true for serum leptin levels. Transfer of RBhigh cells from db/db mice induced delayed disease compared with transfer of WT cells. A high rate of apoptosis in lamina propria lymphocytes and reduced cytokine production were observed early on in scid mice receiving db/db RBhigh cells. These effects were not due to the high levels of glucocorticoids present in db/db mice as administration of corticosterone to WT mice failed to reproduce this phenomenon. High expression of peroxisome proliferator activated receptor γ was observed in the colon of recipients of db/db compared with WT cells. Freshly isolated db/db RBhigh cells produced low levels of interferon γ. Despite delayed onset of colitis, as disease progressed differences between mice receiving WT or db/db cells were no longer apparent. Conclusions: These results suggest that leptin affects the immune response, partly by acting on the long isoform of its receptor expressed on T lymphocytes. [ABSTRACT FROM AUTHOR]

Primary sclerosing cholangitis (PSC) is a chronic cholestatic disorder with a presumed autoimmune aetiopathogenesis. We have recently described a novel organ-specific rat model of fibrosing cholangitis induced by intrabiliary administration of the hapten-reagent 2,4,6-trinitrobenzenesulfonic acid (TNBS) with similarities to human PSC. In the present report, we have evaluated the long-term outcome of TNBS-induced cholangitis in this model. Mild stenosis of the common bile duct of female Lewis rats ( n = 18) was achieved by subtotal ligation and cholangitis induced by TNBS injection (50 mg/kg) into the dilated bile duct after a second laparotomy. After 8 and 12 months, we found no evidence of cholangitis in serum chemistry or histology or retrograde cholangiography of TNBS-treated rats. Antineutrophil cytoplasmic antibodies were positive in 75% of animals but were not predictive of liver damage. Tumour necrosis factor-α levels were not elevated in serum or in mononuclear spleen cell supernatants. Our findings suggest that a single initial insult is not sufficient to trigger chronic progressive inflammation. Rather, perpetuation of inflammation probably requires additional stimuli. [ABSTRACT FROM AUTHOR]