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Neuropeptide Y (NPY) is a key factor in the neurochemical control of food intake, and obstructive cholestasis can be associated with disturbances in food intake. Our aim in this study was to determine whether obstructive cholestasis in the rat is associated with defective central responsiveness to NPY. Cholestasis was induced in rats by surgical bile duct resection. Rats with obstructive cholestasis exhibited a 20% reduction in food intake 2 days after laparotomy (compared with sham-resected controls) that had resolved by 4 days after surgery. Responsiveness to the orexigenic action of NPY was tested by measuring food intake after intracerebroventricular injection of NPY. In sham-resected rats, NPY infusion strikingly increased food intake, whereas bile duct-resected (BDR) rats showed a consistent significantly impaired feeding response to NPY at postlaparotomy days 2, 4, and 7. Separate experiments measured specific binding of [(3)H]NPY to hypothalamic receptors. Fos protein expression was measured in the hypothalamic paraventricular nucleus (PVN) as a marker of NPY-induced neuronal activation. The decreased orexigenic responsiveness to NPY was not caused by altered NPY binding at hypothalamic receptors or its ability to activate neurons in the PVN. Therefore, cholestatic rats demonstrate an attenuated NPY-induced orexigenic drive that occurs early after biliary obstruction, when cholestatic rats exhibit reduced food intake, and persists despite the return of food intake to normal levels and the presence of intact central NPY-related neuronal pathways.

Several lines of evidence suggest a role for mast cells as modulators of gastric mucosal integrity, but the effect of antigenic mast cell activation on mucosal resistance to injury has not previously been examined. In this study, rats were sensitized to the nematode Nippostrongylus brasiliensis and were studied 35-42 days later. With use of an ex vivo gastric chamber preparation, the stomach was exposed for 10 min to 20% ethanol. In some rats, antigen was administered intra-arterially 10 min before application of ethanol. Sensitized rats exhibited similar levels of ethanol-induced gastric injury as control rats, despite having significantly greater numbers of mucosal mast cells. However, antigen administration, which did not in itself produce mucosal injury, significantly augmented (approximately 3-fold) the extent of injury in sensitized but not control rats. Prior treatment with dexamethasone depleted mucosal mast cells in control and sensitized rats. Moreover, this treatment abolished the increase in mucosal injury observed in sensitized rats treated with antigen and topical ethanol. Pretreatment with a leukotriene D4-receptor antagonist, but not a platelet-activating factor-receptor antagonist or a cyclooxygenase inhibitor, abolished the increased susceptibility of sensitized rats to gastric damage induced by antigen and topical ethanol. These results suggest that mucosal mast cell number per se does not influence mucosal susceptibility to injury; however, activation of mast cells markedly increases the susceptibility to injury through a peptidoleukotriene-dependent mechanism.

Hemoproteins have been suggested to contribute to various forms of tissue injury by catalyzing the peroxidation of lipids. In this study, the ability of hemoglobin to catalyze the production of a neutrophil-activating factor from arachidonic acid was examined. Incubation of arachidonic acid, hydrogen peroxide, and hemoglobin at 37 degrees C for 30 min resulted in the production of a lipid-extractable substance that was chemotactic for neutrophils in vitro and could stimulate leukocyte adherence in vivo. These actions could be inhibited by two leukotriene B4 (LTB4) receptor antagonists. The peroxidation product cross-reacted significantly with an antibody directed against LTB4, but not with an antibody directed against LTC4. The production of this factor was hemoprotein dependent. Immunoreactive LTB4 and biological activity were produced only when hemoglobin, or another hemoprotein, cytochrome c, was present in the reaction mixture. The amount of the factor produced could be increased in a concentration-dependent manner by increasing the amounts of arachidonic acid or hydrogen peroxide in the reaction mixture. The production of this factor could be inhibited by 5-aminosalicylic acid, catalase, or deferoxamine. Separation of the lipid-extractable products of the peroxidation of arachidonic acid on high-performance liquid chromatography revealed that the immunoreactive (with anti-LTB4) and chemotactic substance had a retention time distinct from that of LTB4 and the hydroxyeicosatetraenoic acids. A lipid-extractable substance with significant cross-reactivity to anti-LTB4 could also be produced if plasma was substituted for arachidonic acid in the reaction mixture.(ABSTRACT TRUNCATED AT 250 WORDS)