Four in dole alkaloids characterized as 3-isoajmalicine (I-1), 19-epi-3-isoajmalicine (I-2), uncaring B (O-1) and mitraphylline (O-2) were isolated from a Thai native plant, Uncaria salaccensis. The alkaloids were tested on anaesthetized rats in order to determine their effects on blood pressure. Further tests were also performed on isolated rat’s and guinea-pig’s atria to study the alkaloids’ effects on cardiac performance and on neurotransmitter systems of the heart. Hypertensive effect was observed on anaesthetized rats, whereas on isolated hearts, negative chronoscopic, negative isotropic and negative dromotropic responses had been demonstrated. These effects were resistant tp atrp[ome/ {reomcibatopm pf the tossie [re[aratopms wotj the four in dole alkaloids antagonized positive chronoscopic responses of the tissue to 5-hydroxytryptamine. By contrast, responses to adrenaline and isoproterenol remained unaffected. It is concluded that I-1, I-2 and O-2 have antiserotonergic properties. ACKNOWLEDLCEMENT I would like to express my sincere gratitude to my advisor, Dr.Pavich Tongroach, and my co-advospr. Dr.Prasan Dhamma-Upakorn, for their kind advice, guidance, keen interest, and constant encouragement throughout this study. I am also indebted to all staff of the Department of Physiology, Faculty of Pharmacy, Chulalongkorn University, for providing advice and facilities used in experimental works. Apart from the financial support from my parents this study programmer has been made possible partly by chulalongkorn University Graduate School for granting my partial financial support (of fourteen thousand and fifty baht) to conduct this research. To them my gratitude goes. Filly, I would like to extend my appreciation to my parents for their extremely useful support given to me and their encouragement.
