Mast cells induce upregulation of P-selectin and intercellular adhesion molecule 1 on carotid endothelial cells in a new in vitro model of mast cell to endothelial cell communication

It is suggested that mast cells contribute to cell recruitment in inflammation through the upregulation of endothelial adhesion molecules. P-selectin and intercellular adhesion molecule(ICAM)-1 are two key adhesion molecules that have been associated indirectly with mast cell activity. The canine C2 mastocytoma cell line and primary cultures of canine carotid endothelial cells were used to establish a new in vitro model to help study the interaction between mast cells and endothelial cells. Carotid endothelial cells were incubated with mast cell mediators to uncover their effect on endothelial ICAM-1 and P-selectin expression. To assess the relative contributions of tumour necrosis factor (TNF)-alpha and histamine to such effect, an H1 antihistamine and a TNF-alpha blocking antibody were used. Prior to activation by mast cell mediators, P-selectin was expressed only within the cytoplasm, and ICAM-1 was constitutively expressed on the surface of the canine carotid endothelial cells. Both adhesion molecules were enhanced significantly and strongly upon mast cell activation at various time points. Unstored TNF-alpha was fully responsible for ICAM-1 upregulation. P-selectin was up-regulated by both preformed and newly synthesized mast cell mediators, but neither histamine nor TNF-alpha accounted for such an effect. Therefore,a new model is proposed in which the pro-inflammatory effect of mast cells on endothelial cells can be studied in vitro.In this model, it has been demonstrated that only TNF-alpha accounts for the overexpression of ICAM-1 induced by mast cells, and that mast cells up-regulate P-selectin expression through a histamine-independent mechanism.     

Inhibition of rosette formation of IgE-bearing rat mast cells by disodium chromoglycate.

The interaction of reaginic antibody with specific antigen was studied by the rosette formation of peritoneal rat mast cells. The mast cells were obtained from actively sensitized rats or were passively sensitized in vitro. Rosette formation was of a higher degree with mast cells of actively sensitized rats; in this case 58% of the cells showed a strong rosette-forming effect (blinding more than 5 SRBC). No rosette formation was detected in 18% of the cells. With passively sensitized rat mast cells, rosette formation was 45% and 22%, respectively. Rosette formation of both actively and passively sensitized mast cells could be inhibited by disodium chromoglycate (DSCG); the inhibitory effect of 20 micrograms and 200 micrograms of the drug was the same, and neither dose caused a full inhibition. It is suggested that the linkage of specific antigen to the surface of sensitized mast cells can be inhibited by DSCG in vivo.     

The Lectin ArtinM Induces Recruitment of Rat Mast Cells from the Bone Marrow to the Peritoneal Cavity

Background

The D-mannose binding lectin ArtinM is known to recruit neutrophils, to degranulate mast cells and may have potential therapeutic applications. However, the effect of ArtinM on mast cell recruitment has not been investigated.

Methodology

Male Wistar rats were injected i.p. with ArtinM or ConA (control). The ability of the lectin to degranulate peritoneal and mesenteric mast cells was examined. Recruitment of mast cells to the peritoneal cavity and mesentery after ArtinM injection was examined with or without depletion of peritoneal mast cells by distilled water.

Results

ArtinM degranulated both peritoneal and mesentery mast cells in vitro. Three days after i.p. injection of the lectin there were reduced numbers of mast cells in the peritoneal lavage, while at 7 days post injection of ArtinM, the number of peritoneal mast cells was close to control values. Since immature mast cells are recruited from the bone marrow, the effect of the lectin on bone marrow mast cells was examined. Injection of ArtinM resulted in an increased number of mast cells in the bone marrow. To determine if degranulation of mast cells in the peritoneal cavity was required for the increase in bone marrow mast cells, the peritoneal cavity was depleted of mast cells with ultrapure water. Exposure to ArtinM increased the number of mast cells in the bone marrow of rats depleted of peritoneal mast cells.

Conclusions

The ArtinM induced recruitment of mast cells from the bone marrow to the peritoneal cavity may partially explain the therapeutic actions of ArtinM.     

Synthesis of a nitric oxide-like factor from L-arginine by rat serosal mast cells: stimulation of guanylate cyclase and inhibition of platelet aggregation

Rat serosal mast cells were tested for their ability to generate a nitric oxide-like factor by two bioassay systems: inhibition of platelet aggregation and stimulation of mast cell guanylate cyclase. Incubation of rat serosal mast cells with human washed platelets resulted in an inhibition of thrombin-induced platelet aggregation proportional to the number of cells. The inhibition was potentiated by superoxide dismutase (SOD) and reversed by oxyhaemoglobin (oxyHb). The inhibitory activity of mast cells was also prevented by NG-monomethyl-L-arginine (MeArg), an effect reversed by co-incubation with L-Arg but not D-Arg. When mast cells alone were stirred at 1,000 rpm, a time-dependent increase in the levels of their cGMP but not cAMP was observed. This increase was reduced by pretreatment with MeArg. The inhibitory effect of MeArg was reversed by L-Arg but not D-Arg. These results demonstrate that rat mast cells release a factor with the same pharmacological profile as NO, and that this NO-like factor is derived from L-arginine.     

Characterization of the anti-inflammatory effect of FK-506 on human mast cells.

We have examined the effects of FK-506 and of the struturally related macrolide rapamycin, which bind with high affinity to a specific binding protein (FKBP), to evaluate the involvement of this protein in the release of preformed (histamine) and de novo synthesized inflammatory mediators (sulfidopeptide leukotriene C4 and prostaglandin D2) from mast cells isolated from human lung parenchyma. FK-506 (0.1 to 300 nM) concentration dependently inhibited histamine release from lung parenchymal mast cells activated by anti-IgE. FK-506 was more potent in lung mast cells than in basophils (IC50 = 1.13 +/- 0.46 nM vs 5.28 +/- 0.88 nM; p less than 0.001), whereas the maximal inhibitory effect was higher in basophils than in lung mast cells (88.4 +/- 2.5% vs 76.4 +/- 3.8%; p less than 0.01). FK-506 had little or no inhibitory effect on histamine release from lung mast cells challenged with compound A23187, whereas it completely suppressed A23187-induced histamine release from basophils. FK-506 also inhibited the de novo synthesis of 5-lipoxygenase (sulfidopeptide leukotriene C4) and cyclo-oxygenase (prostaglandin D2) metabolites of arachidonic acid from mast cells challenged with anti-IgE. Unlike in basophils, Il-3 (3 to 30 ng/ml) did not modify anti-IgE- or A23187-induced histamine release from lung mast cells nor did it reverse the inhibitory effect of FK-506. Rapamycin (3 to 300 nM) had little or no effect on the release of histamine from lung mast cells, but it was a competitive antagonist of the inhibitory effect of FK-506 on anti-IgE-induced histamine release from human mast cells with a dissociation constant of about 12 nM. These data indicate that FK-506 is a potent anti-inflammatory agent that acts on human lung mast cells presumably by binding to a receptor site (i.e., FKBP).     

Long term increase of mucosal mast cells in the rat induced by administration of Compound 48/80

Summary Administration of Compound 48/80 to rats for 5 days resulted in an increase of the specific type of mucosal mast cell, while connective tissue mast cells elsewhere were almost completely degranulated. The number of mucosal mast cells increased slowly for another 5 days and then returned to the control level, in an exponential manner. The half life of the newly formed mast cells was calculated to be about 40 days. This value may be taken as an estimate of the half life of mucosal mast cells. These cells, therefore, constitute a fraction of mast cells with rapid turnover. Available evidence indicates that the classical connective tissue mast cell has a very long life span, without significant turnover in terms of cell death and cell renewal. We suggest that the increase of mucosal mast cells is an indirect effect of Compound 48/80, related to its effect on other mast cells and mediated by material(s) released from these cells during the secretory process.Supported by grants from the Swedish Medical Research Council, Project no 2235     

Release of 14-kDa group-II phospholipase A2 from activated mast cells and its possible involvement in the regulation of the degranulation process.

Group II phospholipase A2 was detected in appreciable amounts in rat peritoneal mast cells. The effect of several inhibitors specific to 14-kDa group-II phospholipase A2, including two proteinaceous inhibitors and a product of microorganisms with a low molecular mass, on mast-cell activation was examined. When rat peritoneal mast cells were sensitized with IgE and then challenged with antigen, the specific phospholipase-A2 inhibitors suppressed histamine release in a concentration-dependent manner. By contrast, these inhibitors showed no effect on prostaglandin generation under the same conditions. Histamine release from rat peritoneal mast cells subjected to non-immunochemical stimuli, such as concanavalin A, the Ca2+ ionophore A23187, compound 48/80 and substance P was also suppressed. When rat peritoneal mast cells were treated with 14-kDa-group-II-phospholipase-A2-specific inhibitors, washed and stimulated, histamine release was not affected appreciably. Similar suppressive effects of the inhibitors on histamine release were observed with mouse cultured bone-marrow-derived mast cells. When bone-marrow-derived mast cells were activated, they secreted both a soluble and an ecto-enzyme form of 14-kDa group-II phospholipase A2, although appearance of the enzyme associated with the external surface of cells was observed transiently. An appreciable amount of membrane phospholipids was degraded during activation of mast cells, which was decreased by treatment with 14-kDa-group-II-phospholipase-A2 inhibitor. These observations suggest that degranulation and eicosanoid generation in mast cells are regulated independently by discrete phospholipases A2 and that the 14-kDa group-II phospholipase A2 released from mast cells during activation may play an essential role in the progression of the degranulation process.     

IL-4 amplifies the pro-inflammatory effect of adenosine in human mast cells by changing expression levels of adenosine receptors

Adenosine inhalation produces immediate bronchoconstriction in asthmatics but not in normal subjects. The bronchospastic effect of adenosine is largely mediated through adenosine-induced mast cell activation, the mechanism of which is poorly understood due to limitations in culturing human primary mast cells. Here, we show that human umbilical cord blood -derived mast cells incubated with the Th2 cytokine IL-4 develop increased sensitivity to adenosine. Potentiation of anti-IgE- induced and calcium ionophore/PMA-induced degranulation was augmented in mast cells cultured with IL-4, and this effect was reduced or abolished by pre-treatment with A(2B)siRNA and selective A(2B) receptor antagonists, respectively. IL-4 incubation resulted in the increased expression of A(2B) and reduced expression of A(2A) adenosine receptors on human mast cells. These results suggest that Th2 cytokines in the asthmatic lung may alter adenosine receptor expression on airway mast cells to promote increased responsiveness to adenosine.     

Inhibitory effect of diethylstilbestrol on histamine release by rat mast cells and its relation to the cellular ATP content

The effect of diethylstilbestrol, a synthetic estrogen, on mast cell secretion was investigated. The results showed that 50 microM diethylstilbestrol inhibited histamine release from rat peritoneal mast cells in the presence and absence of glucose, but did not affect 45Ca uptake stimulated by concanavalin A. Diethylstilbestrol also inhibited histamine release induced by compound 48/80, exogenous ATP, or ionophore A23187. Since estradiol benzoate, hexestrol and daidzein were not inhibitory, the inhibitory action of diethylstilbestrol must be independent of its estrogenic activity. The ATP content of mast cells decreased to less than 0.1 nmol/10(6) cells on treatment with 50 microM diethylstilbestrol at 37 degrees C for 15 min. This effect of diethylstilbestrol in decreasing the ATP content of mast cells correlated well with its inhibitory effect on histamine release. Diethylstilbestrol at 50 microM depleted the cells of ATP at 37 degrees C, but not at 0 degrees C, whereas [3H]diethylstilbestrol ( [monoethyl-3H]diethylstilbestrol) binding to rat mast cells was the same at 0 and 37 degrees C. It is concluded that diethylstilbestrol reduced the ATP content of rat mast cells by inhibiting metabolism of the cells, and consequently inhibited degranulation.     

A relation between TGF-β and mast cell tryptase in experimental emphysema models

Chronic obstructive pulmonary disease (COPD) is a multicomponent disease characterized by emphysema and/or chronic bronchitis. The aim of this study was to investigate the effect of cigarette smoke exposure on mast cells and mast cell function in vitro and in vivo in order to get further insight in the role of mast cells in the pathogenesis of emphysema. Cigarette smoke conditioned medium (CSM) induced the expression of mast cell tryptase (MMCP-6) in primary cultured mast cells. This tryptase expression was caused by the CSM-stimulated production of TGF-β in culture and neutralization of TGF-β suppressed the CSM-induced expression of tryptase in mast cells. An increase in mast cell tryptase expression was also found in an experimental model for emphysema. Exposure of mice to cigarette smoke increased the number of mast cells in the airways and the expression of mast cell tryptase. In accordance with the in vitro findings, TGF-β in bronchoalveolar lavage fluid of smoke-exposed animals was significantly increased. Our study indicates that mast cells may be a source of TGF-β production after cigarette smoke exposure and that in turn TGF-β may change the tryptase expression in mast cells.     

SCF and TLR4 ligand cooperate to augment the tumor-promoting potential of mast cells

Mast cells may have either antitumor or tumor-promoting potential. Nevertheless, mast cells in tumor microenvironment have been found to promote tumor growth. So far the mechanisms underlying the modulation of mast cell function in tumor microenvironment remains to be fully elucidated. Here, we report that tumor-promoting potential of mast cells could be augmented by molecules released from damaged tumor cells through cooperative stimulation of stem cell factor (SCF) and ligand for Toll-like receptor 4 (TLR4). Co-simulation with SCF and TLR4 ligand inhibited mast cell degranulation, but efficiently induced the production and secretion of VEGF, PDGF, and IL-10. Although TLR4 ligand alone may induce IL-12 expression in mast cells, co-stimulation with SCF and TLR4 ligand induced the expression of IL-10, but not IL-12, in mast cells. The phosphorylation of GSK3β was crucial for the effect of SCF and TLR4 ligand. In addition to inducing phosphorylation of GSK3β at Ser9 through PI3K pathway, SCF and TLR4 ligand cooperated to induce phosphorylation of GSK3β at Tyr216 by simultaneous activation of ERK and p38MAPK pathways. Both phospho-Ser9 and phospho-Tyr216 of GSK3β were required for IL-10 expression induced by SCF/TLR4 ligand, whereas suppressive effect of SCF/TLR4 ligand on mast cell degranulation was related to phospho-Tyr216. Importantly, the effect of SCF and TLR4 ligand on mast cells could be abrogated by inhibiting phosphorylation of GSK3β at Tyr216. These findings disclose the mechanisms underlying the modulation of mast cell function in tumor microenvironment, and suggest that inhibiting GSK3β in mast cells will be beneficial to the treatment of cancer.     

LOCAL MITOGENIC EFFECT OF TISSUE MAST CELL SECRETION

The effect of drug-induced mast cell secretion on proliferation was studied in fibroblast-like and mesothelial-like cells in organ-cultured rat mesentery. Mast cell degranulation achieved by Compound 48/80 was followed by a marked mitogenic reaction in the surrounding tissue cells. The drug itself lacked mitogenic effect on cultured guinea-pig mesentery, the mast cells of which are unresponsive to the drug, and on a human normal fibroblast-like cell line. In contrast, histamine at about 10^?10 M, a major mast cell component, induced marked mitogenesis in guinea-pig mesentery without causing degranulation of mast cells. It is concluded that secreting rat-tissue mast cells release a mitogenic factor or factors acting locally on nearby tissue cells.     

Effects of L-leucine methyl ester (Leu-OMe) on mouse peritoneal mast cells: characterization of histamine release versus cytotoxicity.

L-Leucine methyl ester (Leu-OMe), a lysosomotropic compound, has been found to eliminate several lysosome-rich cellular subtypes and all natural killer cell function from peripheral blood mononuclear cells. In this report, the effect of Leu-OMe on mouse peritoneal mast cells is described. The L-Leu-OMe induced the release of histamine from mouse peritoneal mast cells in a dose-dependent manner (0.25 to 3 mM), while its D-stereoisomer had no effect. L-Leu-OMe displayed also a potent histamine release effect on purified mast cells, indicating a direct effect on mast cells. The monitoring of radioactive chromium release versus histamine release showed that both processes may be unrelated for Leu-OMe concentrations inferior to 1.5 mM. At higher doses, L-Leu-OMe, but not its D-stereoisomer, exerted a potent cytotoxic effect on mast cells. The secretory effect of Leu-OMe was temperature- and energy-dependent. Experiments performed in the absence of extracellular calcium and magnesium demonstrated that these divalent cations were not necessary for the Leu-OMe-induced histamine release, and their deprivation even involved a higher histamine release. The secretory characteristics of the Leu-OMe-induced histamine release appeared to be different from those of the IgE-induced ones. These results support the conclusion that exposure of mouse peritoneal mast cells to high doses of L-Leu-OMe results in killing of these cells, that are new targets of this lysosomotropic agent.     

Selective adhesion of mast cells to tracheal epithelial cells in vitro

In allergic and nonallergic lung diseases, if intraluminal mast cells adhere to airway epithelium, inflammatory mediators released from activated mast cells may reach high local concentrations and thus greatly affect airway function. To determine whether mast cells adhere to airway epithelial cells, radiolabeled or unlabeled dog mastocytoma cells were incubated with cultured dog tracheal epithelial cells, with extracellular matrix substrates, and with cryostat-cut sections of dog trachea. Mast cells adhered well to cultured epithelial cells (35 +/- 13% adhesion, mean +/- 1 SD, n = 23) but adhered poorly to types I and IV collagen or to fibronectin (less than 7.5% mean adhesion in all cases). Similarly, in tracheal tissue sections, mast cells adhered preferentially to epithelial cells in surface epithelium or in submucosal glands but not to basal membrane or connective tissue. Adhesion to cultured epithelial cells was a characteristics of a subpopulation of mast cells, could persist for more than 48 h, did not require energy or the presence of divalent cations, and was not mediated by a known family of leukocyte-associated adhesion glycoproteins. Adhesion was completely abolished by pretreatment of mast cells with pronase E or proteinase K but not with trypsin (up to 10 micrograms/ml at 37 degrees C for 20 min each). In contrast, pretreatment of cultured epithelial cells with any of these proteinases had no effect on adhesion. It is concluded that dog mastocytoma mast cells adhere to dog tracheal epithelial cells and do so selectively. It is suggested that mast cell adhesion to airway epithelium may play a role in the effectiveness of mast cell-epithelial cell interactions, and thus, in certain lung diseases, airway function may be affected by intraluminal mast cells more than is currently appreciated.     

IL-4 modulates the histamine content of mast cells in a mast cell/fibroblast co-culture through a Stat6 signaling pathway in fibroblasts

IL-4 plays a crucial role in the pathogenesis of allergic diseases, such as the induction of IgE synthesis and the development of mast cells. To further understand the effect of IL-4 on mast cells in skin, we utilized a mast cell/fibroblast co-culture system as an in vitro model of dermal mast cells. IL-4 induced mast cell growth in the culture with fibroblasts. Immunoblot analysis revealed that IL-4 activated Stat6 in both mast cells and fibroblasts. The over-expression of dominant-negative Stat6 in fibroblasts in the presence of IL-4 decreased the histamine content per mast cell, but not the number of mast cells. In contrast, the over-expression of constitutively-active Stat6 in fibroblasts increased the histamine content per mast cell, indicating that the activation of Stat6 in fibroblasts supports the maturation of mast cells co-cultured with fibroblasts.     

尼罗罗非鱼消化道肥大细胞的组化性质

实验采用改良甲苯胺蓝(MTB)、阿利新蓝-沙黄(AB/SO)、甲基绿-派洛宁(MG-P)、天青Ⅱ-伊红-瑞氏混合液和硫堇5种组化染色法,对尼罗罗非鱼(Nile tilapia)消化道组织中的肥大细胞(Mast cell,MC)组化性质进行研究。尼罗罗非鱼的食管、胃及小肠壁内均显示有肥大细胞,在食管和胃的切片标本上肥大细胞主要分布在黏膜固有层和胃腺体之间。在肠道中的肥大细胞主要分布在黏膜固有层和肠上皮下方,少量肥大细胞存在于黏膜下层结缔组织中。细胞呈圆形、椭圆形,也有长梭形的。而且肥大细胞有沿血管分布的特点。5种组化染色结果表明:AB/SO、MTB和MG-P显示的MC效果较好,尤其AB/SO染色效果最好,肥大细胞轮廓清楚,胞质颗粒较清晰;尼罗罗非鱼肥大细胞胞浆颗粒都呈红色,即肥大细胞胞浆主要含肝素,不含组胺。天青Ⅱ-伊红-瑞氏混合液染色效果也很好,但被染的肥大细胞较少;80%乙醇硫堇染色,在尼罗罗非鱼消化道各段组织中均未能鉴定出肥大细胞。尼罗罗非鱼消化道肥大细胞大多分布于浅层的黏膜或血管、腺体周围的结缔组织等易表露于环境抗原的位点。罗非鱼消化道黏膜层结缔组织中的肥大细胞与大多数脊椎动物的肥大细胞一样,具有沿血管分布的特性,说明硬骨鱼的肥大细胞如哺乳动物肥大细胞一样与血管有着密切的关系。       

Effect of a single neonatal endorphin treatment on the hormone content of adult rat white blood cells and mast cells

Using flow cytometry and confocal microscopy, the presence of endorphin, serotonin and chorionic gonadotropin (hCG) was demonstrated in rat white blood cells and peritoneal mast cells. After a single neonatal treatment with beta-endorphin (hormonal imprinting), the mast cells of female rats reaching adulthood contained significantly less endorphin and serotonin, as well as slightly less hCG, than control cells. There was no change in the hormone content of the mast cells of males. The lymphocytes, monocytes and granulocytes of both sexes also contained the three hormones, but endorphin imprinting had no effect on these cells.     

Mast cell-mediated allergic response is suppressed by Sophorae flos: inhibition of SRC-family kinase

Complementary and alternative medicines are considered as a promising direction for the development of anti-allergic therapies in oriental countries. We screened approximately 100 oriental herbal medicines for anti-allergic activity. Sophorae flos exhibited the most potent effect on degranulation in antigen-stimulated mast cells. We further investigated the effect of Sophorae flos on the IgE-mediated allergic response in vivo and its mechanism of action in mast cells. Sophorae flos exhibited a significant inhibitory effect on degranulation in antigen-stimulated mast cells with IC(50) values of approximately 31.6 microg/mL (RBL-2H3 mast cells) and approximately 47.8 microg/mL (bone marrow-derived mast cells). Sophorae flos also suppressed the expression and secretion of TNF-alpha and IL-4 in the cells and IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. Sophorae flos inhibited the activating phosphorylation of Syk and LAT in mast cells. Further downstream, activating phosphorylation of Akt and the prototypic MAP kinases, namely, p38, ERK1/2, and JNK, were also inhibited. These results suggest that Sophorae flos inhibits the Src family kinase-dependent signaling cascades in mast cells and may thus exert anti-allergic activity.     

Enhanced intracellular calcium induced by urocortin is involved in degranulation of rat lung mast cells.

Corticotropin-releasing factor (CRF), which activates the hypothalamic-pituitary- adrenal axis under stress, also has proinflammatory peripheral effects possibly through mast cells. The purpose of this study was to investigate the effect of urocortin (UCN), a 40-amino-acid CRF family peptide, on degranulation and intracellular calcium of rat lung mast cells. The activation and degranulation of mast cells were observed by Toluidine blue staining and transmission electron microscope. The intracellular calcium was investigated using confocal laser scanning microscopy and flow cytometry. The results indicated that all the three different concentrations of UCN (0.1, 1 and 10 microM) significantly induced the activation and degranulation of rat lung mast cells in vitro. This effect was markedly blocked by selective CRF receptor 1 (CRF-R1) antagonist antalarmin, but not by specific CRF receptor 2 (CRF-R2) antagonist antisauvagine-30 (anti-Svg-30). The results also showed that UCN caused a rapid peak increase in [Ca(2+)](i) at point of 300s after UCN treatment, followed by a decrease to a sustained plateau phase. The peak increase in [Ca(2+)](i) induced by UCN was significantly inhibited by antalarmin, but not by anti-Svg-30. This effect of UCN on [Ca(2+)](i) in rat lung mast cells was also found by flow cytometry. Regression analysis revealed a positive correlation between mast cells degranulation extent and the maximum value of [Ca(2+)](i) (P < 0.01). Taken together, our present study suggested that UCN induced the increase of [Ca(2+)](i) and degranulation of rat lung mast cells through CRF-R1. These findings may have implications for the pathophysiology of allergic and inflammatory lung disorders such as asthma, which is closely associated with mast cell activation and degranulation.     

Vasoactive intestinal peptide inhibits degranulation and changes granular content of mast cells: a potential therapeutic strategy in controlling septic shock

Vasoactive intestinal peptide (VIP) has potent protective activity against sepsis and increases the survival rate of septic rats and mice. The present study was planned to evaluate the effect of VIP on mast cell activity, histamine and methylhistamine levels and oxidative stress in the liver and kidneys of septic rats. The effect of VIP was compared to that of nitric oxide synthesis inhibition, previously tested extensively in septic shock models, with doubtful benefit. The present study showed that endotoxic shock did not lead to oxidative stress in either liver or kidney of the rats. On the other hand, mast cells, based on their location, displayed functional heterogeneity to the septic insults. VIP possibly modulated the specific reactions of the tissues to mediators released from mast cells during septic shock. The most prominent effect of VIP as compared to nitric oxide synthesis inhibition was related to mast cells. In conclusion, the prevention of mast cell reactivity by VIP could be a potential therapeutic strategy in controlling septic shock.