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: C_max = 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 (C_max = 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.