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

Abstract

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 microns 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.

Figure 1

Faecal pH in different sections of small intestine in untreated rats (control), indomethacin treated rats fed with standard diet (ST/ST), indomethacin treated rats fed with a diet poor of fat, later rich in fat (FP/FR), and rats treated with potassium hydrogen citrate without indomethacin (HCl). Mean values are shown.

Figure 2

Correlation between faecal pH and indomethacin induced leucocyte adherence in rats fed with standard diet without (control) or with indomethacin (ST/ST) and treated with various diet combinations or alkalising drugs 10 days after indomethacin administration. Mean values are shown. y = −2.5x + 24.1 for the regression line, r=−0.55, p<0.05.

Figure 3

Correlation between faecal pH on venular wall shear rate in rats fed with standard diet without (control) or with indomethacin (ST/ST) and treated with various diet combinations or alkalising drugs 10 days after indomethacin administration. Mean values are shown. y = 87.8x − 278 for the regression line, r=0.48, p<0.05.

Figure 4

Correlation between faecal pH and macroscopic ulcer score in rats fed with standard diet without (control) or with indomethacin (ST/ST) and treated with various diet combinations or alkalising drugs 10 days after indomethacin administration. Mean values are shown. y = −0.3x + 29.4 for the regression line, r=−0.67, p<0.05.