loaded into both apical and basolateral chambers. After incubation at 37uC for 1 h, 5 mM digoxin was added to either apical or basolateral side to evaluate the transport in absorptive and secretory direction ” respectively. After incubation for just another 2 h, samples were taken from the receiving chamber for analysis. Verapamil was used as a positive control. Digoxin was determined by LC-MS/MS. All experiments were conducted in triplicate. and autosampler tray temperatures were 40 and 4uC, respectively. The mobile phase was 
consisted of methanol, acetonitrile and 0.1% formic acid with gradient elution. Mass spectrometer was operated in positive ESI mode. MS parameters were as follows: spray voltage, 5.0 kV; sheath gas/auxiliary gas, nitrogen; sheath gas pressure, 356105 Pa; auxiliary gas pressure, 206105 Pa; ion transfer capillary temperature, 300uC. Quantification was performed using SIM mode with peak: m/z 645.4 for Rh2; m/z 483.3 for Ppd; m/z 787.5 for digitoxin. Data analysis The pharmacokinetic parameters of digoxin, 20-Rh2 and 20-Rh2 in rats were obtained by noncompartmental analysis using DAS. The area under the plasma concentration-time curve was calculated using the trapezoidal method. For the transport assay, the apparent permeability coefficient and efflux ratio were calculated as reported previously. Data are expressed as mean 6 S.E.. Comparisons for betweengroups were performed using Student’s t test. For multiple comparisons, one-way analysis of variance followed by Post-Hoc test was adopted. The difference was considered to be statistically significant if the probability value was less than 0.05. Effects of 20-Rh2 and 20-Rh2 on Adriamycin Sensitivity in P-gp highly-expressed MCF-7/Adr Cells MTT colorimetric assay was used to measure the cell growth inhibition after incubation with various concentrations of adriamycin in the absence or presence of 20-Rh2 or 20-Rh2 at 37uC for 72 h. The concentrations required to inhibit growth by 50% were calculated from survival curves using the Bliss method. Acknowledgments The authors wish to 313348-27-5 biological activity sincerely thank Dr. Chaonan Zheng, Hua Ai and Yuan Sun, Dr. Yi Gu and Dr. Yu Lu for their kind assistance and hard work in the performance of the experiments and the review of the paper. LC-MS analysis of 20-Rh2, 20-Rh2 and the deglycosylation metabolites 20 – Ppd and 20-Ppd The 20-Rh2, 20-Rh2 and the deglycosylation metabolites 20-Ppd and 20-Ppd were quantified simultaneously by reversed-phase LC-MS. An aliquot of 100 ml sample spiked with digitoxin as internal standard was extracted by 1 ml ethylacetate. The analysis was performed on Finnigan LC-MS system with a Lux Cellulose-1 Chiral Column. The phytopathogenic oomycete Pseudoperonospora cubensis, the causative agent of cucurbit downy mildew, infects a wide range of cucurbits, including cucumber, squash, and melon. As an obligate biotroph, Ps. cubensis is dependent on its host for both reproduction and dispersal, and as such, has evolved a highly specialized host range limited to members of the Cucurbitaceae. At present, downy mildew is the most important foliar disease of cucurbits, affecting cucurbit production throughout the world. Under favorable conditions, Ps. cubensis is capable of infecting and defoliating a field in less than two weeks, and as a result, is responsible for devastating “8560673 economic losses. For more than 50 years, control of downy mildew on cucumber in the U.S. was maintained through genetic resistance; however, since 2004,