In situ intestinal absorption kinetics of valsartan in rats

The aim of this study was to investigate the absorption mechanism of valsartan in various intestinal segments. Single-pass intestinal perfusion (SPIP) model was used to study the intestinal absorption kinetics of valsartan and the effects of drug transporters,including P-glycoprotein (P-gp) and organic anion transporting polypeptide (OATP),on in situintestinal absorption at different segments in rats.Valsartan was assayed by RP-HPLC. Valsartan was absorbed in the whole intestine,and its absorption rate of valsartan was influenced by the pH of the perfusion solution and intestinal segments. The absorption rate was descended as the order of duodenum,jejunum，colon and ileum. Valsartan absorption can be described best by nonlinear dynamic absorption parameters (K_a=0.328 h^-1;Vm=72.652 μmol/(L·h);Km=10.968 μmol/L;Vms=69.115 μmol/(L·h);Kms=0 μmol/L).The absorption rate constants (K_a) in jejunum，colon and ileum were estimated to be (0.595±0.091),(0.586±0.153) and (0.551±0.030) h^-1,respectively.Group containing P-gp inhibitor had marked increased of P_app,while for OATP inhibitor, P_app was significantly decreased (P<0.05).In conclusion,the intestinal absorption mechanism of valsartan was demonstrated to be the combination of active transport and passive diffusion,according with the nonlinear kinetics.