Role of platelet-activating factor in leukocyte-independent plasma extravasation and mast cell activation during endotoxemia

Pharmacokinetics and tissue distribution of ginkgolide A, ginkgolide B, and ginkgolide K after intravenous infusion of ginkgo diterpene lactones in a rat model

Ginkgo diterpene lactones are compounds that are extracted from the Ginkgo biloba leaf and possess pharmacologic activities with neuroprotective effects. To address the poor bioavailability of ginkgo diterpene lactones, ginkgo diterpene lactone meglumine injection (GDLI) was formulated and is commercially available. In this study, a simple, sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for assessing the total amount and the amount of the prototype forms of ginkgolides A (GA), B (GB) and K (GK) in rat plasma and tissues. This method was used to calculate the concentrations of the hydrolysed carboxylic forms and assess the pharmacokinetics of the ginkgolides after intravenous (i.v.) GDLI administration in rats. Generally, all three ginkgolide forms showed dose-dependent plasma concentrations, and no obvious differences in pharmacokinetic parameters, i.e., area under the curve (AUC) of plasma concentration versus time and half-life, were observed after GDLI administration on 7 consecutive days. These ginkgolides primarily existed in the carboxylic form in the plasma, and the systemic concentrations of the carboxylic forms of GA and GB were 11- to 17- and 3- to 4-fold higher than those of their prototype forms, respectively. In contrast, dramatically increased levels of the GA and GB prototype lactones were detected in the liver and heart. GA, GB, and GK were extensively distributed in various organs/tissues; the highest levels were found in the kidneys, liver, and intestine, and the lowest levels were found in the brain. These data suggest that ginkgolides have difficulty crossing the blood-brain barrier and that their targets for protecting against cerebral ischaemia are located outside the central system.

Mechanism of action of antiplatelet drugs on decompression sickness in rats: a protective effect of anti-GPIIbIIIa therapy

Literature highlights the involvement of disseminated thrombosis in the pathophysiology of decompression sickness (DCS). We examined the effect of several antithrombotic treatments targeting various pathways on DCS outcome: acetyl salicylate, prasugrel, abciximab, and enoxaparin. Rats were randomly assigned to six groups. Groups 1 and 2 were a control nondiving group (C; n = 10) and a control diving group (CD; n = 30). Animals in Groups 3 to 6 were treated before hyperbaric exposure (HBE) with either prasugrel (n = 10), acetyl salicylate (n = 10), enoxaparin (n = 10), or abciximab (n = 10). Blood samples were taken for platelet factor 4 (PF4), thiobarbituric acid reactive substances (TBARS), and von Willebrand factor analysis. Onset of DCS symptoms and death were recorded during a 60-min observation period after HBE. Although we observed fewer outcomes of DCS in all treated groups compared with the CD, statistical significance was reached in abciximab only (20% vs. 73%, respectively, P = 0.007). We also observed significantly higher levels of plasmatic PF4 in abciximab (8.14 ± 1.40 ng/ml; P = 0.004) and enoxaparin groups (8.01 ± 0.80 ng/ml; P = 0.021) compared with the C group (6.45 ± 1.90 ng/ml) but not CD group (8.14 ± 1.40 ng/ml). Plasmatic levels of TBARS were significantly higher in the CD group than the C group (49.04 ± 11.20 μM vs. 34.44 ± 5.70 μM, P = 0.002). This effect was prevented by all treatments. Our results suggest that abciximab pretreatment, a powerful glycoprotein IIb/IIIa receptor antagonist, has a strong protective effect on decompression risk by significantly improving DCS outcome. Besides its powerful inhibitory action on platelet aggregation, we suggest that abciximab could also act through its effects on vascular function, oxidative stress, and/or inflammation.

Platelet activating factor contributes to vascular leak in acute dengue infection

Background

Although plasma leakage is the hallmark of severe dengue infections, the factors that cause increased vascular permeability have not been identified. As platelet activating factor (PAF) is associated with an increase in vascular permeability in other diseases, we set out to investigate its role in acute dengue infection.

Materials and Methods

PAF levels were initially assessed in 25 patients with acute dengue infection to determine if they were increased in acute dengue. For investigation of the kinetics of PAF, serial PAF values were assessed in 36 patients. The effect of dengue serum on tight junction protein ZO-1 was determined by using human endothelial cell lines (HUVECs). The effect of dengue serum on and trans-endothelial resistance (TEER) was also measured on HUVECs.

Results

PAF levels were significantly higher in patients with acute dengue (n = 25; p = 0.001) when compared to healthy individuals (n = 12). In further investigation of the kinetics of PAF in serial blood samples of patients (n = 36), PAF levels rose just before the onset of the critical phase. PAF levels were significantly higher in patients with evidence of vascular leak throughout the course of the illness when compared to those with milder disease. Serum from patients with dengue significantly down-regulated expression of tight junction protein, ZO-1 (p = 0.004), HUVECs. This was significantly inhibited (p = 0.004) by use of a PAF receptor (PAFR) blocker. Serum from dengue patients also significantly reduced TEER and this reduction was also significantly (p = 0.02) inhibited by prior incubation with the PAFR blocker.

Conclusion

Our results suggest the PAF is likely to be playing a significant role in inducing vascular leak in acute dengue infection which offers a potential target for therapeutic intervention.

Although plasma leakage is the hallmark of severe dengue infections, the factors that cause increased vascular permeability have not been identified. As platelet activating factor (PAF) is associated with an increase in vascular permeability in other diseases, we set out to investigate its role in acute dengue infection. In this study, we found that PAF was significantly increased in patients with DHF, and the PAF levels rose just before the onset of the critical phase of dengue, during which vascular leak is thought to occur. PAF in serum of dengue patients was associated with reduced expression of tight junction proteins (ZO-1) and reduction in trans-endothelial resistance (TEER) of human endothelial cells. Use of PAFR blockers significantly reduced the down regulation of ZO-1 by serum of dengue patients and also the reduction of TEER, suggesting that PAF plays a significant role in inducing vascular leak in acute dengue infections.

n-3 PUFA induce microvascular protective changes during ischemia/reperfusion

Ischemia/reperfusion (I/R) injury can occur in consequence of myocardial infarction, stroke and multiple organ failure, the most prevalent cause of death in critically ill patients. I/R injury encompass impairment of endothelial dependent relaxation, increase in macromolecular permeability and leukocyte-endothelium interactions. Polyunsaturated fatty acids (n-3 PUFA), such as eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) found in fish oil have several anti-inflammatory properties and their potential benefits against I/R injury were investigated using the hamster cheek pouch preparation before and after ischemia. Before the experiments, hamsters were treated orally with saline, olive oil, fish oil and triacylglycerol (TAG) and ethyl ester (EE) forms of EPA and DHA at different daily doses for 14 days. Fish oil restored the arteriolar diameter to pre ischemic values during reperfusion. At onset and during reperfusion, Fish oil and DHA TAG significantly reduced the number of rolling leukocytes compared to saline and olive oil treatments. Fish oil, EPA TAG and DHA TAG significantly prevented the rise on leukocyte adhesion compared to saline. Fish oil (44.83 ± 3.02 leaks/cm(2)), EPA TAG (31.67 ± 2.65 leaks/cm(2)), DHA TAG (41.14 ± 3.63 leaks/cm(2)), and EPA EE (30.63 ± 2.25 leaks/cm(2)), but not DHA EE (73.17 ± 2.82 leaks/cm(2)) prevented the increase in macromolecular permeability compared to saline and olive oil (134.80 ± 1.49 and 121.00 ± 4.93 leaks/cm(2), respectively). On the basis of our findings, we may conclude that consumption of n-3 polyunsaturated fatty acids, especially in the triacylglycerol form, could be a promising therapy to prevent microvascular damage induced by ischemia/reperfusion and its consequent clinical sequelae.

High-dose vitamin C treatment reduces capillary leakage after burn plasma transfer in rats

Oxidative stress after burn injuries leads to systemic capillary leakage and leukocyte activation. This study evaluates whether antioxidative treatment with high-dose vitamin C leads to burn edema reduction and prevention of leukocyte activation after burn plasma transfer. Donor rats underwent a burn (n = 7; 100 degrees C water, 12 seconds, 30% body surface area) or sham burn (37 degrees C water; n = 2) procedure and were killed after 4 hours for plasma harvest. This plasma was administered to study rats (continuous infusion). Rats were randomized to four groups (n = 8 each; burn plasma alone [BP]; burn plasma/vitamin C-bolus 66 mg/kg and maintenance dose 33 mg/kg/hr [VC66]; burn plasma/vitamin C-bolus 33 mg/kg and maintenance dose 17.5 mg/kg/hr [VC33]; and sham burn plasma [SB]). Intravital fluorescence microscopy in the mesentery was performed at 0, 60, and 120 minutes for microhemodynamic parameters, leukocyte adherence, and fluorescein isothiocyanate-albumin extravasation. No differences were observed in microhemodynamics at any time. Burn plasma induced capillary leakage, which was significantly higher compared with sham burn controls (P < .001). VC66 treatment reduced microvascular barrier dysfunction to sham burn levels, whereas VC33 had no significant effect. Leukocyte sticking increased after burn plasma infusion, which was not found for sham burn. Vitamin C treatment did not influence leukocyte activation (P > .05). Burn plasma transfer leads to systemic capillary leakage. High-dose vitamin C treatment (bolus 66 mg/kg and maintenance dose 33 mg/kg/hr) reduces endothelial damage to sham burn levels, whereas half the dose is inefficient. Leukocyte activation is not influenced by antioxidative treatment. Therefore, capillary leakage seems to be independent from leukocyte-endothelial interactions after burn plasma transfer. High-dose vitamin C should be considered for parenteral treatment in every burn patient.

Effects of activated protein C on post cardiac arrest microcirculation: an in vivo microscopy study

BACKGROUND

The clinical symptoms and pathophysiologic mechanisms during and after ischaemia-reperfusion following cardiac arrest (CA) and successful cardiopulmonary resuscitation (CPR) closely resemble those observed in patients with severe sepsis. Impairment of microcirculation and endothelial leakage seem to play key roles in the underlying pathophysiology. Recombinant human activated protein C (rhAPC) is the first drug being licensed for the treatment of severe sepsis in patients. Therefore, for the first time, we investigated effects of rhAPC on microhaemodynamic changes and endothelial leakage applying in vivo microscopy of postcapillary mesenteric venules after CA and CPR in rats.

METHODS

After 6 min of CA, male Wistar rats were randomised into two groups (n=10) to receive rhAPC or placebo (0.9% NaCl). Sham-operated animals (n=10) served as non-ischaemic controls. At 360, 420, and 480 min after CA in vivo microscopy was performed to assess wall shear rate (WSR) and plasma extravasation (PE).

RESULTS

Both treatment groups showed typical signs of impaired microcirculation and a severe endothelial leakage after CA at all time points studied when compared to the sham group. However, no significant differences between the treatment groups were observed with regard to WSR and PE.

CONCLUSION

Our results show that CA with consecutive successful CPR leads to a microcirculatory impairment closely resembling experimentally induced sepsis. Intriguingly, despite these similarities, rhAPC had no significant effects on WSR and PE. Our results strongly suggest that further mechanisms such as mast cell activation might play an important role and have therefore to be studied to elucidate the pathophysiology of "postresuscitation disease".

In vivo fluorescence microscopic imaging for dynamic quantitative assessment of intestinal mucosa permeability in mice

Herein, we introduce a novel intravital microscopic method to quantitatively assess mucosal permeability in mouse intestine. To this end, the time course of changes in the accumulation of fluorescent markers (sodium fluorescein [MW 376] and fluorescent dextran [FD4000, MW 4000; Merck, Darmstadt, Germany]) was examined in the perivascular interstitium of the mesentery of sham-operated animals and animals undergoing 30 min intestinal ischemia and 90 min postischemic reperfusion. An increased permeation of intraluminally installed sodium fluorescein was found only in the late reperfusion period, while permeability was enhanced during the entire postischemic examination period when renal excretion of the fluorescent marker was excluded by kidney ligation. Similarly, the late reperfusion phase was associated with enhanced tissue fluorescence to FD 4000 when the kidneys were ligated. Fluorescence values in the plasma, as measured by standard fluorimetry, showed a significant correlation with tissue fluorescence determined by intravital microscopy. Further, villus tip denudation at 90 min reperfusion correlated with increased permeability of sodium fluorescein in the early (10-20 min) and FD 4000 in the late reperfusion phase (90 min). Thus, intravital microscopic measurement of mesenteric perivascular fluorescence provides a simple and easily applicable on-line method to quantitatively assess epithelial permeability, allowing to detect altered mucosal barrier function and to evaluate salvage therapies which target mucosal integrity.

Role of Antithrombin and Factor XIII In Leukocyte-Independent Plasma Extravasation During Endotoxemia: An Intravital-Microscopic Study in the Rat

BACKGROUND

Platelet-endothelial interactions have been shown to be main mediators of leukocyte-independent endothelial damage. Besides altering platelet-endothelial interactions, both antithrombin and factor XIII reduce microvascular permeability in leukocyte-dependent experimental models. Thus, it was our aim to investigate the effects of antithrombin and factor XIII on microvascular permeability during leukocyte-independent endotoxemia.

MATERIAL AND METHODS

In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline, 60, and 120 min after the start of the experiment. Fucoidin and a continuous infusion of lipopolysaccharides were used to generate leukocyte-independent endotoxemia. The experiment was divided into two parts 1) an antithrombin study and 2) a factor XIII study.

RESULTS

No differences between groups in leukocyte rolling and venular wall shear rate could be observed in both parts of the experiment. Pretreatment with antithrombin reduced microvascular permeability significantly compared with control subjects (120 min: Fuco [untreated]: 0.14 +/- 0.03; Fuco/ETX [control]: 0.37 +/- 0.06; Fuco + ATIII/ETX: 0.15 +/- 0.02; P < 0.05). Factor XIII reduced microvascular permeability significantly after 60 min (Fuco [untreated]: 0.10 +/- 0.03; Fuco/ETX [control]: 0.36 +/- 0.07; Fuco + FXIII/ETX: 0.13 +/- 0.04; P < 0.05). This effect diminished after 120 min (Fuco [untreated]: 0.12 +/- 0.03; Fuco/ETX [control]: 0.5 +/- 0.08; Fuco + FXIII/ETX: 0.29 +/- 0.05; P < 0.05).

CONCLUSIONS

Antithrombin and factor XIII reduce leukocyte-independent microvascular permeability. Yet, factor XIII also shows a nonprotective effect on a long-term basis. These data emphasize the central role of platelets in leukocyte-independent endotoxemia.

Activation of the liver X receptor protects against hepatic injury in endotoxemia by suppressing Kupffer cell activation

Recent reports have demonstrated that liver X receptors (LXRs) of the nuclear receptor family have anti-inflammatory effects on macrophages. Here we examine whether activation of LXR by the synthetic agonist GW3965 can ameliorate the liver injury/dysfunction caused by endotoxins in the rat. Male Wistar rats received GW3965 (0.3 mg/kg) or vehicle (50% dimethyl sulfoxide) 30 min before coadministration of lipopolysaccharide (LPS, 5 mg/kg i.v.) and peptidoglycan (1 mg/kg i.v.). Treatment with GW3965 attenuated the increase in the plasma levels of alanine aminotransferase and bilirubin (markers of liver injury/dysfunction) as well as the focal hepatocyte necrosis (histology) caused by coadministration of LPS and peptidoglycan. This protective effect of GW3965 treatment was associated with reduced infiltration of mast cells in the liver (histopathology) and reduced gene expression of the chemokines eotaxins 1 and 2, whereas MIP-2 mRNA levels were not affected. Plasma levels of tumor necrosis factor alpha and prostaglandin E2 were significantly attenuated by GW3965, whereas plasma interleukins 6 and 10 were not altered. High expression of LXRalpha mRNA was observed in Kupffer cell cultures, suggesting that Kupffer cells are targets of GW3965. Subsequent in vitro studies in Kupffer cells demonstrated that exposure to GW3965 attenuated the LPS-induced release of tumor necrosis factor alpha and prostaglandin E2 in a dose-dependent manner. In conclusion, this study demonstrates that activation of LXR by GW3965 protects against liver injury and dysfunction in a rat model of endotoxemia, in part by exerting an anti-inflammatory effect on Kupffer cells.

Cyclic nucleotide second messengers (cAMP and cGMP) play a central role in signal transduction and regulation of mesenteric postcapillary fluid leak

BACKGROUND

Endothelial cell receptors involved in post-injury/sepsis fluid extravasation are coupled to G-proteins that stimulate production of cGMP and cAMP. We hypothesize that cGMP and cAMP are endothelial second messengers that control microvascular permeability. The purposes of this series of experiments are to determine microvascular permeability under the following conditions: 1) reduced cGMP levels, 2) elevated cGMP levels, 3) reduced cAMP levels, and 4) elevated cAMP levels.

METHODS

Rat mesenteric venules were cannulated and hydraulic permeability (Lp) was measured at 3 to 5 minute intervals during 1) cGMP synthesis inhibition, 2) inhibition of cGMP degradation, 3) cAMP synthesis inhibition, and 4) inhibition of cAMP degradation (n = 6 in each study group). Lp units are x10 cm(-7)/sec/cmH2O and represented as mean +/- SEM.

RESULTS

Compared with baseline Lp (1.10 +/- 0.06), reduced cGMP levels by inhibiting its synthesis decreased Lp by over 50% (0.50 +/- 0.02, p < 0.001), while elevated cGMP levels by preventing its degradation increased Lp by more than 2-fold (0.91 +/- 0.10 to 2.26 +/- 0.15, p < 0.001). The reduction of cAMP levels by synthesis inhibition elevated Lp over 400% from 0.92 +/- 0.04 to 4.11 +/- 0.54 (p < 0.001), and elevation of cAMP level by blocking its degradation reduced Lp almost 50% from 1.11 +/- 0.04 to 0.59 +/- 0.06 (p < 0.001).

CONCLUSIONS

The second messengers, cGMP and cAMP, contribute to the control mechanisms that govern fluid leak across the endothelial barrier: cGMP increases microvascular permeability, while cAMP decreases microvascular permeability. Endothelial cell cyclic nucleotide second messengers are pharmacologically accessible and may be targeted during post-injury/sepsis-associated microvascular fluid leak.

Modulation of microvascular hydraulic permeability by platelet-activating factor

BACKGROUND

Platelet-activating factor (PAF) is a modulator of the inflammatory response to shock. Edema formation and intravascular fluid loss have been associated with PAF. The increase in microvessel permeability caused by PAF may be related to direct endothelial cell activation and leukocyte activation. We hypothesized that PAF increases hydraulic permeability by means of the direct activation of endothelial cells.

METHODS

Hydraulic permeability (Lp) was measured in rat mesenteric venules using the modified Landis micro-occlusion technique. After baseline Lp measurements, paired measures of Lp were obtained during PAF perfusion at doses of 0.1 nmol/L (n = 6), 1.0 nmol/L (n = 6), 10 nmol/L (n = 6), and 50 nmol/L (n = 6). The temporal effects of pulse administration of PAF and repeated exposures to PAF were also assessed.

RESULTS

Compared with baseline values (Lp = 1.16 +/- 0.11), the Lp of the microvessels significantly increased at PAF doses of 0.1 nmol/L (Lp = 1.46 +/- 0.1) (p < 0.002), 1 nmol/L (Lp = 2.0 +/- 0.11) (p < 0.004), 10 nmol/L (Lp = 4.09 +/- 0.09) (p < 0.005), and 50 nmol/L (Lp = 5.13 +/- 0.07) (p < 0.0001). All units for Lp are given as +/- SE x 10 -7 cm s-1. cm H2O-1.

CONCLUSION

PAF increased microvessel permeability in a dose-dependent manner. The permeability-increasing effect of PAF was transient even with continuous endothelial exposure to PAF. This study emphasizes the ability of PAF to directly modulate microvascular permeability and increase venular permeability.

Role of nitric oxide in leukocyte-independent endothelial damage during experimental endotoxemia

Endothelial damage during early endotoxemia has been shown to be leukocyte independent. Platelet-activating factor and serotonin receptor antagonism has been shown to reduce leukocyte-independent macromolecular leakage significantly. Nevertheless, the exact mechanisms involved in leukocyte-independent endothelial dysfunction are unknown. Therefore, it was the aim of the study to investigate the effects of nitric oxide (NO) on leukocyte-independent endothelial damage during endotoxemia. In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline and at 60 and 120 min after start of the experiment. The animals received fucoidin to prevent leukocyte-endothelial interaction. The experiments were divided into three parts. In part 1, we investigated the effects of the NO-inhibitor L-NAME on leukocyte-independent endothelial damage during endotoxemic and nonendotoxemic conditions. The efficiency of the NO-donor (SIN-1) used, part 2, was investigated by the inhibitory properties of SIN-1 on NO-inhibition-induced macromolecular efflux. Finally, part 3, we analyzed the effects of the NO-donor SIN-1 on endothelial damage during endotoxemia. Both the combined challenge of the animals with L-NAME and endotoxin and the challenge with L-NAME alone resulted in a strong increase in macromolecular efflux, showing significant differences to control groups at an earlier time point than endotoxin challenge alone. Interestingly, combined L-NAME and endotoxin challenge, L-NAME challenge alone, and endotoxin challenge alone showed a similar macromolecular efflux at the end of the experiment. SIN-1 prevented both the increase in macromolecular efflux seen after L-NAME challenge (part 2) and was highly effective in preventing significantly the increase in macromolecular leakage that is seen during leukocyte-independent endotoxemia (part 3). In conclusion, our data indicate that during early states of endotoxemia endogenous NO preserves endothelial integrity in a leukocyte-independent setting. Exogenous NO prevents endothelial damage during early leukocyte-independent endotoxemia. Summarizing these data, endothelial integrity during leukocyte-independent endotoxemia is a NO-mediated event.

Mesenteric microvascular inflammatory responses to systemic hypoxia are mediated by PAF and LTB4

Systemic hypoxia produces a rapid microvascular inflammatory response characterized by increased reactive oxygen species (ROS) levels, leukocyte-endothelial adherence and emigration, and increased vascular permeability. The lipid inflammatory mediator leukotriene B(4) (LTB(4)) is involved in the early hypoxia-induced responses (ROS generation and leukocyte adherence). Whether other lipid inflammatory mediators participate in this phenomenon is not known. The objective of these experiments was to study the role of platelet-activating factor (PAF) in the microvascular inflammatory response to hypoxia and its potential interactions with LTB(4) in this response. Intravital microscopy was used to examine mesenteric venules of anesthetized rats. We found that WEB-2086, a PAF receptor antagonist, completely prevented the increase in ROS levels and leukocyte adherence during a brief reduction in inspired Po(2) to anesthetized rats; administration of either WEB-2086 or the LTB(4) antagonist LTB(4)-DMA attenuated leukocyte emigration and the increase in vascular permeability to the same extent during prolonged systemic hypoxia in conscious rats. Furthermore, no additive effect was observed in either response when both antagonists were administered simultaneously. This study demonstrates a role for PAF in the rapid microvascular inflammatory response to hypoxia, as well as contributions of PAF and LTB(4) to the slowly developing responses observed during sustained hypoxia. The incomplete blockade of the hypoxia-induced increases in vascular permeability and leukocyte emigration by combined administration of both antagonists indicates that factors in addition to LTB(4) and PAF participate in these phenomena.

Influence of serotonin-receptor antagonism on mast cell activation during endotoxemia

INTRODUCTION: Mast cells have been implicated in the aetiology of many diseases and are particularly important in evoking leukocyte-endothelial interactions during endotoxemia. Mast cell activity can be modified by histamine. There are only little data available whether serotonin (5-HT), another amine, is involved in alterations of mast cell activity, too. The aim of the study was to investigate the effects of the 5-HT-receptor antagonists methysergide (5-HT(1/2/7)-receptor antagonist), and ketanserin (5-HT(2A)-receptor antagonist) on mesenteric mast cell activation during endotoxemia. MATERIALS AND METHODS: In male Wistar rats, mast cell activity was determined in the mesentery using intravital microscopy. Rats were randomised in four groups of 12 animals each. Animals underwent laparotomy and the mesentery was exposed beneath an in-vivo videomicroscope. After baseline measurment endotoxemia was induced by continuous intravenous infusion of 2 mg/kg/h endotoxin (ETX group). Animals in the ETX/5-HT(1/2)-ANT group received methysergide (1 mg/kg body weight), animals in the ETX/5-HT(2A)-ANT group received ketanserin (1 mg/kg body weight) additionally prior to laparotomy and to the procedure described above. Animals in saline group served as controls and received equivalent volumes of NaCl 0.9%. Activated mast cells were stained by superfusion of the mesentery with ruthenium red. RESULTS: The relative mast cell activity to baseline value increased significantly in all groups. Values of the ETX-group versus the ETX/5-HT(1/2)-ANT group, the ETX/5-HT(2A)-ANT group, and the saline group were significantly higher at 120 min. CONCLUSIONS: Serotonin receptor antagonism using the 5-HT(1/2/7)-receptor antagonist methysergide or the 5-HT(2A)-receptor antagonist ketanserin reduces endotoxin-induced mast cell activation in-vivo, most probably via the 5-HT(2A)-receptor subtype.

Methysergide attenuates leukocyte-independent plasma extravasation during endotoxemia

PURPOSE

During endotoxemia, the early endothelial damage has been shown to be leukocyte independent. Therefore, it was the aim of our study to investigate the role of serotonin in mediating leukocyte-independent microvascular permeability during endotoxemia. Microvascular permeability was determined after inhibition of the L-selectin mediated leukocyte adherence by fucoidin and after inhibition of serotonin effects by the serotonin (5HT)-receptor antagonist methysergide.

MATERIALS AND METHODS

In male Wistar rats, leukocyte rolling, leukocyte adherence, and macromolecular leakage were determined in mesenteric postcapillary venules using intravital microscopy. After pretreatment with the serotonin-receptor antagonist methysergide, animals in the FUCO/ETX/5HT-ANT group received a continuous infusion of endotoxin. Animals in the FUCO/ETX group underwent the same procedure but received saline 0.9% instead of methysergide. In both groups, leukocyte adherence was prevented by administration of fucoidin. Animals in the saline group received volume-equivalent saline 0.9%.

RESULTS

In the endotoxin-challenged groups, fucoidin prevented leukocyte rolling and reduced leukocyte adherence to values comparable to saline group. In the FUCO/ETX group, macromolecular leakage increased significantly, starting at 60 minutes. Values in the saline group increased slightly, being significant at 120 minutes, whereas vascular permeability remained unchanged in the FUCO/ETX/5HT-ANT group. Differences in macromolecular leakage between the FUCO/ETX-group versus the FUCO/ETX/5HT-ANT group and the saline group were significant at 120 minutes. Differences in macromolecular leakage between the FUCO/ETX/5HT-ANT group and the saline group were not significant.

CONCLUSIONS

The leukocyte-independent endothelial damage during early endotoxemia can be inhibited efficiently by the 5-HT-receptor antagonist methysergide, indicating that serotonin plays an important role in that pathophysiology.