OBJECTlVE To investigate the inhibition of Radix lsatidis and its major constituents indigo and indirubin on three principal subtypes of organic anion transporters ( OATs) , Oat1, Oat2 and Oat3 in vivo in mice. METHODS Granules of Radix lsatidis ( GRl) 0.615 and 2.46 g·kg-1 , decoction of Radix lsatidis ( DRl) 1.6 and 6.4 g·kg-1 , indigo 0.008 and 0.64 mg·kg-1 and indirubin 0.0192 and 1.536 mg·kg-1 were ig given to the NlH mice (60 mice per group), twice a day, for 5 d while four control groups were set up, including vehicle of water, 0.5%sodium carboxymethyl cellulose ( CMC) , positive control probe-necid (0.05 g·kg-1) and additives of sucrose plus dextrin (1.5 g·kg-1 each) groups. After the last dosing of the test samples, para-aminohippuric acid ( PAH) clearance test was conducted. All the mice were iv given PAH 0.03 g·kg-1 and 1, 2.5, 5, 7.5, 10 and 20 min later before 10 mice per group were euthanized to collect whole blood and the kidneys were quickly removed. Each right kidney was homoge-nized to analyze the PAH accumulations and each left kidney to extract total mRNA for analysis of Oat1, Oat2 and Oat3 gene expressions using quantitative real-time PCR. The concentrations of PAH in sera and in kidney homogenates were determined by the method of Kiguchi. Major pharmacokinetic parame-ters of PAH in sera were calculated by pharmacokinetic software ( DAS2.0) . PAH uptake test for kidney slices was performed on another group of NlH mice according to the method of Nakakariya. RESULTS There was no significant difference between water control group and 0.5%CMC group in all the examined items. Compared with the vehicle control groups ( water and 0. 5%CMC group ) , elimination half time ( t1/2β) of PAH in GRl 2.46 g·kg-1 ,indigo 0.64 mg·kg-1 and indirubin 1.536 mg·kg-1 groups was signifi-cantly prolonged (P<0.05), the total clearance (Cl) and volume of distribution (Vd) were obviously reduced ( P<0.01) and the area under the curve ( AUC0-20 min ) of PAH in all the tested groups was signifi-cantly increased ( P<0.01) . AUC0-20 min obtained from renal PAH accumulations within the checked time was significantly higher ( P<0.05, P<0.01) than in the vehicle control group. But there was in no signifi-cant difference between all the study groups in kidney-to-plasma AUC ratios. PAH uptake results by kidney slices were significantly lower ( P<0. 05, P<0. 01 ) than in vehicle control group in every two dosages of all the four samples tested. Compared with vehicle control group, the mRNA expressions of Oat1, Oat2 and Oat3 were obviously ( P<0.05, P<0.01) and abnormally regulated in the groups of GRl 2.46 g·kg-1, DRl 6.4 g·kg-1, indigo 0.64 mg·kg-1 and indirubin 1.536 mg·kg-1. CONCLUSlON The renal Oat1, Oat2 and Oat3 of mice are significantly inhibited by GRl, DRl, indigo and indirubin. The inhibitory function of Radix lsatidis probably stems from indigo and indirubin contained in it.