ABSTRACT
Studies using isolated rat fundus strip preparation demonstrated that l-stephanine ( l-STP ) , l-roemerine ( 1-REM ), l-stepholidine (l-SPD), 1-tetrahydropalmatine ( l-THP ) and dl-tetrahydrode-berine ( THB ) possessed 5-HT blockade properties. 1-STP ( 16, 25 ?M ) produced competitve antagonism against 5-HT receptor on rat fundus, while higher concentration ( 50 ?M ) suggested a non-competi tive inhibition, with pA2' and2' values equal to 5.8 and 4.2 respectively. 1-REM was found to be a non-competitive antagonIst ( pD' 2 = 4.5). 1-SPD, 1-THP and THB cuased a parallel shift to the right of 5-HT concentration response curve without any significant changes in their maximum response, indicating that they were competitive antagonists of 5-HT receptor. The antagonistic potencies of 1-SPD, l-THP and THB were expressed as pA2 values: 6.2,5.2 and 5.0.