This report presents the in vitro study of pharmacological effects of three members in the diterpenoid lactone group (andrographolide, neoandrographolide and 14-deoxy-11, 12-didehydroandreorapholide) which were extracted from a native Thai plant named Andrographis paniculata (Burm.f.) Wall. ex Nees. In the dose of 1.5 x 10-5 and 1.5 x 10-6 M. they had antispasmodic effect on isolated rat and mice stomach smooth muscle preparation. Their effects on rat stomach strips showed non-competitive antagonism to spasmogenic activity of acetylcholine and in rat stomach strips depolarized by potassium chloride in high concentration, they showed competitive antagonism to spasmogenic activity of calcium chloride. In depolarizing condition, their competitive antagonistic effects were the same as those obtained from 5 x 10-8 M. verapamil. The inhibitory potencies were dose-dependent. In whole isolated mice stomach, the extracts reduced phasic and tonic contraction, especially in tonic phase, induced by acetylcholine and calcium chloride. The results of the present study indicated that the extracts were non-specific antagonist. Although several mechanisms are possible, the results suggest that they may act as calcium-entry blocker. The antispasmodic effect supports the clinical use of this native plant in diarrheal disorder of the gastrointestinal tract.
