A comparison of prednisolone absorption and the effect of sodium salicylate and mannitol in normal and damaged rat bowel

A model of ulcerated bowel was produced in the rat rectum by treatment with Brij 35 suppositories. Prednisolone absorption from enemas in normal and damaged bowel was assessed using an in situ rectal loop. In animals 20 h after damage drug absorption was reduced but returned to normal levels after one week. Co-administration of equiosmolar sodium salicylate (1 and 2% w/v) and mannitol (2.5 and 4.1% w/v) solutions in normal bowel induced a significant water flux into the lumen and changed the plasma tritium profile compared to the control. In damaged bowel plasma tritium levels remained low following co-administration of mannitol (2.5% w/v) but were restored to normal control levels by co-administration of salicylate (1% w/v). The altered absorption in normal bowel can be attributed in part to osmotic stress but in damaged bowel the difference between the effect of equiosmotic solutions of salicylate and mannitol suggests that a different mechanism is operating.