Studies on intestinal absorption mechanism and influential factors of Cinnamic acid in rats

The mechanism and effect of the PH, drug solution concentration, intestinal segments, P-gp on Cinnamic acid absorption in rat´s intestine were investigated by using in situ single-pass perfusion technique in rats. Results showed that the absorbed dose of Cinnamic acid was increased linearly and no saturation of high concentration was observed when drug concentration was in rang of 0.02-0.10 mgmiddotml^-1, suggesting the passive diffusion mechanism. The absorbed dose, absorption rate constant (Ka), and apparent absorption coefficient (Papp) sequence (from high to low) of Cinnamic acid in the perfusate of different PH was 5.8, 6.8, 7.8, 8.8, and the PH between 5.8 and 8.8 was significantly different (P<0.05). The absorption parameters of ileum, jejunum, duodenum in paired comparison had no significant difference (P>0.05), and were obviously higher than that of colon (P<.05), which demonstrated that the absorption of Cinnamic acid was influenced by PH and didn´t contain a special absorption window in small intestine. Besides, P-glycoprotein (P-gp) inductor rifampicin evidently inhibited the absorption of Cinnamic acid in intestine, and P-gp inhibitor verapamil was just the opposite. These results suggested that it was a P-gp substrate, and we could improve its bioavailability by combining with P-gp inhibitor.