Pharmacological basis of contractile effects of peptidoleukotrienes on rabbit colonic muscularis mucosae

Muscularis mucosae contraction evokes colonic secretion via prostaglandin synthesis and nerve stimulation

This in vitro study tested the hypothesis that muscularis mucosae contractile activity contributes to rabbit colonic mucosal function by mechanisms other than simple mechanical deformation of the epithelium. Experiments were performed by using a technique that allows simultaneous recording of muscle activity and transmucosal potential difference, a measure of epithelial ion transport. ATP, bradykinin, histamine, PGE(2), PGF(1alpha), and PGF(2alpha) elicited muscularis mucosae contractions that were resistant to atropine and TTX. Only ATP-induced contractions were indomethacin sensitive, and only those to dimethylphenylpiperazinium iodide (DMPP) were reduced by atropine. All agonist-evoked increases in transmucosal potential difference were atropine resistant, and, with the exception of those to PGE(2), PGF(2alpha), and VIP, they were also TTX sensitive. Mucosal responses to ATP, bradykinin, and histamine were indomethacin sensitive, whereas those to DMPP, the prostaglandins, and VIP were not. When cyclooxygenase activity or the mucosal innervation was compromised, even maximal muscularis mucosae contractions did not produce large secretory responses. It is concluded that contraction-related prostaglandin synthesis and noncholinergic secretomotor neuron stimulation represent the physiological transduction mechanism through which muscularis mucosae motor activity is translated into mucosal secretion.

Early vascular permeability in murine experimental peritonitis is co-mediated by resident peritoneal macrophages and mast cells: crucial involvement of macrophage-derived cysteinyl-leukotrienes

The initial phase of zymosan-induced peritonitis involves an increase of vascular permeability (peak at 30 min) that is correlated with high levels of vasoactive eicosanoids, namely, prostaglandins (PGI2 and PGE2) of cyclooxygenase-1 origin (as estimated by RT-PCR) and cysteinyl-leukotrienes. Previously, we showed that the increase of vascular permeability can be attributed only partially to mast cells and their histamine, as seen in mast cell-deficient WBB6F1-W/Wv mice. Thus we aimed to identify the major cellular source(s) that mediate vasopermeability, as well as particular vasoactive mediators operating in this model. For this purpose, some mice were selectively depleted of either peritoneal macrophages or mast cells, and/or they were treated with several pharmacologic inhibitors of cyclooxygenase- and lipoxygenase-metabolic pathways. More-over, macrophage-depleted mast cell-deficient WBB6F1-W/Wv mice and their controls (+/+) were used. The macrophage depletion always caused a profound decrease of both vascular permeability and lipid-mediator levels, which was particularly pronounced for leukotrienes, whereas the effects of mast-cell depletion were less severe. The macrophage/mast-cell co-mediation of vasopermeability was also revealed in thioglycolate-induced peritonitis, as well as the macrophage origin of cysteinyl-leukotrienes. Taken together, these findings demonstrate that the resident peritoneal macrophages are in fact the main contributors to the vasopermeability at the early stages of zymosan-induced peritonitis.

Serum from NSAID-treated patients attenuates the capacity of rat leukocytes to synthesize leukotriene B4

The synthesis of leukotriene B4 by A23187-stimulated rat peritoneal leukocytes was studied in the presence of 0.1% normal human serum, serum from patients treated with NSAIDs for either an inflammatory (rheumatoid arthritis, RA) or a non-inflammatory condition (lumbar disc protrusion, LDP), and serum from RA patients drawn one week after withdrawal from NSAID treatment. The capacity for LTB4 synthesis was significantly lower in the presence of serum from NSAID treated patients: thirty per cent less than observed in presence of normal serum in the RA group, and fifty per cent in the LDP group. When NSAIDs were withdrawn from RA patients, the LTB4 production in presence of serum increased, but was not completely normalized after one week. These results indicate that NSAID treatment may down-regulate the capacity for leukotriene synthesis by an indirect effect.