Difference absorption of l-tetrahydropalmatine and dl-tetrahydropalmatine in intestine of rats

To investigate the difference in absorptive of tetrahydropalmatine (THP) and l-tetrahydropalmatine (l-THP) in rat intestine as well as the mechanism of the absorption of THP, in situ single pass perfusion model was used and the concentration of THP in perfusate was determined by HPLC. The absorption rate constant (k_a) and effective permeability values (P_eff) of THP had no significant difference (P>0.05) at concentration of 8, 16 and 32 μg·mL^-1 in perfusion or in four different regions of intestine of rat (duodenum, jejunum, ileum, colon). The absorption of l-THP and THP in jejunum had significant difference (P<0.05). The k_a and P_eff of THP increased obviously when verapamil was co-perfused with THP, while those of l-THP were not influenced by verapamil. The absorption of THP in intestine showed the passive diffusion process, and without a special absorption region. The stereoselective absorption difference may result from stereoselective combination of P-glycoprotein with d-THP.