Abstract Objective To observe the preventive effect and mechanism of piperine on gallbladder stone formation in New Zealand rabbits. Methods: 1. Animal model: 30 New Zealand rabbits were randomly divided into: control group (10 rabbits), fed normal diet; stone group (10 rabbits), fed lithogenic diet containing 1 2 g/d cholesterol for 4 weeks; piperine group (10 rabbits), fed piperine diet containing 1 2 g/d cholesterol and 0 0 4 5 g/d for 4 weeks. 2. Aminopeptidase N (APN) expression: The changes of hepatic APN mRNA level were detected by RT PCR method. 3. APN activity: The activity was detected by chemical method. Results: 6 (6/10) gallbladder stones and 9 (9/10) cholesterol crystals were found in the stone group, while no stones and crystals were found in the piperine group and the control group; APNmRNAIOD ratio in the stone group (0 6 5± 0 18 in the control group, 1 0 8± 0 35 in the stone group, 0 87± 0 4 4 in the piperine group), APN activity (6 1± 2 5 3U/L in the control group, 2 3 6 4 ± 10 36U/L in the stone group), and APN activity in the control group. The APN activity (6 1± 2 5 3 U/L in the control group, 2 3 6 4 in the stone group, 10 36 U/L in the piperine group, 8 31± 6 47 U/L in the piperine group) was significantly higher than that of the control and piperine groups. Conclusion The above results suggest that piperine can prevent the formation of cholesterol stones mainly by reducing the expression of hepatic APN and the activity of biliary APN enzyme and inhibiting the lithogenic effect of APN… More