Leucocyte endothelial cell adhesion in indomethacin induced intestinal inflammation is correlated with faecal pH

Background—Recent studies indicate that faecal pH is acidified in patients with inflammatory bowel disease compared with healthy controls. In healthy volunteers, stool pH, faecal flora, and bile acid concentration could be affected by means of elemental diets.Aims—To assess the role of variations of faecal pH on leucocyte endothelial cell adhesion in indomethacin induced long lasting ileitis in rats.Methods—Indomethacin (7.5 mg/kg subcutaneously) was injected twice, 24 hours apart. Rats were either fed with the identical diet before and 10 days after the induction of inflammation until the experiment, or the diet was changed at the time of induction. Ten postcapillary mesenteric venules (30 μm diameter) per animal were observed using intravital microscopy. Macroscopic visible intestinal ulceration was scored and faecal pH of different sections of the small bowel was determined.Results—Small intestinal faecal pH was 8.5 in controls and 8.0 in indomethacin treated animals. Indomethacin significantly changed microcirculatory parameters: there was a 2.3-fold increase in leucocyte adherence, a 3.2-fold increase in leucocyte emigration, and a 20% reduction in shear rate. Application of various diets or diet combinations resulted in variations in faecal pH ranging from 7.8 to 8.8 which were inversely correlated with macroscopic ulcerations (r=−0.67). Leucocyte adherence was attenuated with increased pH and augmented with decreased pH (r=−0.55). Venular wall shear rate was positively correlated with faecal pH (r=0.48) while leucocyte emigration showed no correlation. Leucocyte rolling velocity was not significantly altered. Normalisation of faecal pH by different alkalising drugs induced a significant decrease in leucocyte adherence in standard fed, indomethacin treated rats.Conclusions—Faecal pH is lowered in the indomethacin model of long lasting ileitis in rats, which is similar to human inflammatory bowel disease. Alkalisation of faecal pH due to different diets or alkalising drugs reduces indomethacin induced leucocyte endothelial cell adhesion and macroscopic intestinal damage. These results may provide a rationale for the therapeutic effect of enteral diets in Crohn’s disease.

Studies on the gastric mucosal microcirculation. 2.Helicobacter pylori water soluble extracts induce platelet aggregation in the gastric mucosal microcirculation in vivo

Background—The exact mechanisms by whichHelicobacter pylori infection results in gastric mucosal injury are unclear.Aims—To assess in vivo whether H pylori extracts could initiate an inflammatory response in the rat gastric mucosal microcirculation.Methods—Extracts of H pylori, Escherichia coli, or distilled water were administered topically to the gastric mucosa of anaesthetised animals. Fluorescence in vivo microscopy assessed macromolecular leakage of labelled albumin from mucosal vessels, leucocyte adherence/rolling, and platelet activity for 90 minutes.Results—H pylori induced increases (p<0.001) in adherent platelet thrombi and circulating platelet emboli after five and 15 minutes respectively. Adherent platelet thrombi (mean of four per field of view) remained significantly increased throughout the experiment, but circulating emboli (maximum of five at 30 minutes) decreased with time. Leucocyte adherence did not occur although early transient rolling was observed. An 11% increase (p<0.02) in albumin leakage occurred after five minutes only. The induction of platelet aggregation was only observed following H pyloriadministration.Conclusion—This in vivo study demonstrated the ability of Hpylori extracts to promote platelet aggregation within gastric mucosal microvessels. Recruitment of leucocytes was not observed. The results suggest that the early events associated with H pylori infection are platelet aggregation with perhaps subsequent leucocyte recruitment by activated platelets.

Effects of a thiol antioxidant on leucocyte adherence to aortic endothelium during atherogenesis: Quantitative SEM assessment

Dysfunction of arterial endothelial cells (EC) leading to adherence of circulating leucocytes (WBC) is a pivotal step in atherogenesis, preceding fatty streak formation. The attachment process is mediated at least in part by inducible endothelial-leucocyte adhesion molecules (ELAMs) on the EC surface which interact with WBC counterreceptors. Expression of VCAM-1, a monocyte selective adhesion molecule, by IL-1 and TNF stimulated vascular EC in vitro was shown to be inhibited by a thiol antioxidant (pyrrolidine dithiocarbamate, PDTC). In this study we analyzed the effect of PDTC administered to cholesterol-fed rabbits, on WBC attachment to lesion-prone sites of the aorta using SEM morphometry.New Zealand White (NZW) rabbits (2-3 kg) were fed 1% cholesterol for 3 d. The day before feeding, venous cannulas were introduced, and PDTC (20 mg/kg) or vehicle (0.1 M PBS) was given twice daily throughout. The animals were euthanatized at 4 d and the aortas pressure perfusion fixed with buffered 2.5% glutaraldehyde after rinse with Ringer‘s solution containing heparin (10 u/ml).