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. 1998 Sep;43(3):356–364. doi: 10.1136/gut.43.3.356

Correlation of desensitisation of platelet activating factor (PAF) receptors with intensity of inflammation and intestinal PAF content during experimental ileitis in guinea pig

O Jeanneton 1, M Delvaux 1, Y Langlois 1, P Le Bars 1, J Le Bars 1, M Delisle 1, J Frexinos 1, L Bueno 1
PMCID: PMC1727237  PMID: 9863481

Abstract

Aim—To determine the kinetics of platelet activating factor (PAF) and prostaglandin E2 (PGE2) receptor desensitisation during intestinal inflammation induced by trinitrobenzenesulphonic acid (TNB) instillation and to study the relation between receptor regulation, inflammatory lesions, and PAF content of the gut wall. 
Methods—Receptor desensitisation was assessed on isolated smooth muscle cells from the circular layer. PAF content of the intestinal wall was determined by thin layer chromatography and radioimmunoassay. 
Results—After an acute inflammatory phase on day 1, subacute changes appeared in TNB instilled ileum, with a maximal intensity on day 6. In control animals, PAF 10 nM and PGE2 10 nM provoked a maximal contraction in the range of 24% of cell shortening. On days 1 and 3 after intestinal instillation of TNB, PAF induced contraction was not altered whereas the effect of PGE2 was progressively desensitised (2 logM rightward shift of its concentration-response curve: Cmax = 1 µM; p<0.01). Between days 4 and 6, the concentration-response curve of PGE2 shifted by only 1 logM (p<0.05) whereas the curve of PAF induced contraction shifted by 2 logM (Cmax = 1 µM; p<0.01). The PAF content of the ileal wall was maximal between days 3 and 5 (300 ng/mg tissue). On days 10 and 15, PAF and PGE2 induced contractions were similar to those observed on day 1, and PAF content returned to basal. 
Conclusion—Inflammation induced by TNB instillation triggers PAF and PGE2 receptor desensitisation; this is dependent on the duration of inflammation and correlates with PAF content in the ileum. This receptor desensitisation may play a protective role by preventing overstimulation of intestinal smooth muscle cells. 



Keywords: platelet activating factor receptor; prostaglandin E2 receptor; receptor desensitisation; intestinal inflammation; trinitrobenzensulphonic acid; smooth muscle cells

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Figure 1 .

Figure 1

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Normal histological pattern of the ileum six days after instillation of saline into the lumen (haemalun/eosin stain; original magnification × 6.3). 


Figure 2 .

Figure 2

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Acute inflammation induced by trinitrobenzenesulphonic acid (TNB) instillation into the lumen of guinea pig ileum. On day 1 after the instillation, the lesions are mainly characterised by the presence of oedema in the submucosa and the infiltration of mononuclear cells and neutrophils and mucosal erosions (haemalun/eosin stain; original magnification × 16). 


Figure 3 .

Figure 3

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Second phase of the inflammation provoked by trinitrobenzenesulphonic acid (TNB) in guinea pig ileum. Villi are destroyed. The mucosa is largely eroded by deep ulcerations. Infiltration into the submucosa is maximal (day 3) (haemalun/eosin stain; original magnification × 6.3). 


Figure 4 .

Figure 4

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Subacute phase of inflammation with fibrosis in the submucosa. Ulcerations are less deep than in the earlier stages of inflammation (day 6) (haemalun/eosin stain; original magnification × 6.3). 


Figure 5 .

Figure 5

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Inflammatory index characterising morphological changes in intestinal wall after instillation of trinitrobenzenesulphonic acid (TNB). Five animals were killed at each time point and the inflammatory index was measured for each of the samples. Data are shown as mean (SEM). The inflammatory index is statistically significantly different from that on day 0, except on days 4, 10, and 15. 


Figure 6 .

Figure 6

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Kinetics of desensitisation of platelet activating factor (PAF; solid circles) and prostaglandin E2 (PGE2; open circles) receptors of smooth muscle cells of the circular layer, after intraluminal instillation of trinitrobenzenesulphonic acid (TNB) into guinea pig ileum (mean (SEM) of samples obtained at each time point from five different animals). The concentration of PAF and PGE2 inducing maximal contraction (Cmax) of the cells is expressed in logM and plotted against time elapsed between TNB instillation and the killing of the animals. Values of Cmax significantly different from control animals treated with saline: *p<0.05; **p<0.01. 


Figure 7 .

Figure 7

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Time relationship of platelet activating factor (PAF) receptor desensitisation in intestinal smooth muscle cells (solid circle) after trinitrobenzenesulphonic acid (TNB) instillation and PAF content in the ileum, after intraluminal instillation of saline (open squares) or TNB (solid squares) in guinea pig ileum. PAF content was evaluated by thin layer chromatography on the various days after TNB treatment (mean (SEM) for samples obtained at each time from five different animals). The concentration of PAF inducing a maximal cell contraction did not change over time in saline treated animals and is not shown. Statistically significant differences are quoted as follows: *p<0.05, **p<0.01, ***p<0.001 for comparison between TNB treated animals and values at D0; °p<0.05, °°°p<0.001 for comparison between saline and values at D0; †p<0.05, ††p<0.01, †††p<0.001 for comparison between TNB and saline treated animals at the same time interval from surgery. On day 1 after intraluminal instillation of TNB, we observed a moderate increase in PAF content of the gut wall (165 (22) ng/mg tissue) (NS) (table 3). Three days after TNB treatment, PAF content was maximal in injured ileum (348 (31) ng/mg tissue) (p<0.001), and was significantly higher than that measured on day 3 in ileum from saline treated animals (p<0.01). The PAF content remained at this high level for the next 2 days (days 4 and 5). From day 6, it decreased and returned to basal level by day 10 (200 (9) ng/mg tissue). On day 15, the amount of PAF in the ileum from TNB treated animals increased again (215 (30) ng/mg tissue) and was significantly higher than that measured in untreated animals (day 0) (109 (13) ng/mg tissue) (p<0.05). 


Selected References

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