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Finally, intestinal absorption of compounds A and H were also investigated by Caco-2 monolayer cell model. These results demonstrated, for the first time, that these stemona alkaloids were well absorbed in a gastrointestinal cell culture model. Furthermore, compound A was demonstrated to have a marked preference in the basolateral to apical transport direction, and such efflux (basolateral to apical) transport was inhibited by both verapamil and cyclosporine A, P-glycoprotein (P-gp) inhibitors, but not by probenecid and MK371, multidrug resistant-associated protein (MRP) inhibitors. The results suggested that compound A transported through active efflux mechanisms via P-gp but not MRP pathway.High performance liquid chromatography (HPLC) coupled with evaporative laser scattering detector (ELSD) was developed to qualitatively and quantitatively determine the chemical profiles of Radix Stemonae. The results demonstrated that the type and quantity of the main bioactive ingredients, stemona alkaloids, present in various herbal samples varied significantly. Compound A (neotuberostemonine) was identified as a predominant alkaloid in two commercial Radix Stemonae samples, whereas compound F (croomine), compound H (tuberostemonine) and compound G (oxoneotuberostemonine) were identified as the major alkaloids present in other three commercial samples, respectively. Chemical variations were observed in several fresh Radix Stemona samples collected in mainland China. These chemical variations might be due to species and/or environmental differences.In addition to the antitussive activities, it was found that a high dose of compound A caused markedly behavioral changes, including head and body shaking via both intraperitoneal and intracerebroventricular administration. Such adverse effect was abolished by a centrally acting dopamine D2 antagonist haloperidol, suggesting that a central dopaminergic effect might contribute to the behavioral activities produced by compound A. Moreover, compound A was found, for the first time, to dose-dependently and competitively inhibit monoamine oxidase (MAO)-B and compound A was identified to be a weak and non-competitively inhibitor on MAO-A. It was further demonstrated that compound A increased the intercellular concentration of dopamine in the cultured PC12 cells and prevented MPTP-induced cell death in PC12 cells via inhibition of MAO. Therefore, the behavioral changes induced by compound A was suggested to be involved with dopaminergic pathway via reduction of dopamine metabolism caused by inhibition of MAO.On the other hand, compound F was demonstrated to cause acute lethal toxicity via intraperitoneal but not via oral administration. The results suggested that compound F might have a low oral bioavaiIability. Further absorption study by Caco-2 model demonstrated that this alkaloid had a good intestinal absorption, thus its low oral bioavailability could be due to extensive first-pass effects in the gastrointestinal tract.Pharmacological properties of stemona alkaloids were studied in vivo using the citric acid-induced guinea pig cough model. The three stemona alkaloids present in different Radix Stemonae samples were all found to be antitussive. Compounds A and H were both orally active and had similar antitussive potencies via both oral and intraperitoneal (i.p.) administrations. Compound F was demonstrated to be antitussive via i.p. administration only. The mechanism of antitussive activity of the representative stemona alkaloid, compound A, was further investigated. However, none of the currently known antitussive pathways were identified to be involved in compound A. Thus, compound A and also other stemona alkaloids are likely to produce their antitussive activity via a novel pathway.Radix Stemonae is derived from the root tubes of three different species of Stemona genus (Stemonaceae). This herb has been prescribed in traditional Chinese medicine (TCM) as an antitussive agent for over thousands of years. To date, over fifty stemona alkaloids have been identified from various Stemona species. However, there is a lack of direct evidence to link stemona alkaloids to the effectiveness of the herb in the treatment of cough. The aim of the present study is to investigate Stemona species used as plant sources for Radix Stemonae, the chemical and pharmacological properties in relation to antitussive activity of the herb, and the intestinal absorption of the main bioactive constituents, stemona alkaloids, in the herb.The identity of fresh Radix Stemonae samples was investigated using a DNA based polymorphism assay. 5S-rRNA, ITS-1 and ITS-2 are highly conserved spacer regions; thus, the diversity of these spacer regions was used for the identification of Radix Stemonae samples. The amplified spacer regions of different Radix Stemona samples collected from different geographical locations in Mainland China were sequenced and compared. The result demonstrated that there were at least three different DNA patterns among seven samples examined and this DNA sequential assay could distingue species in Stemona genus from species in other genera. However, the findings suggested that the variation in chemical profiles of different Radix Stemonae samples was not directly related to their DNA sequences. DNA sequential method could be used to authenticate the correct plant sources for Radix Stemonae but it can not to provide information on chemical profiles of the herb.The overall results demonstrated that the quantities and types of stemona alkaloids varied significantly depending upon plant sources. Furthermore, these stemona alkaloids differed considerably in pharmacological activities, toxicological effects and absorption profiles. Therefore, these variations in different Radix Stemonae samples may lead to different therapeutic outcomes, including efficacies, adverse effects, and potential herb-drug and herb-herb interactions. Nevertheless, the present study provided a scientific basis for the therapeutic use of Radix Stemonae and illustrated a potential for the development of herbal Radix Stemonae or pure stemona alkaloids into a new class of antitussive TCM herbal products or TCM-based agents in the future.Leung Pak Ho Henry."January 2006."Adviser: Ge Lin.Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6328.Thesis (Ph.D.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (p. 179-197).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstracts in English and Chinese.School code: 1307