Mechanism of the Hypotensive Effect of Scopoletin Isolated from the Fruit of Tetrapleura tetraptera

Abstract

The plausible mechanisms of the hypotensive effect of scopoletin, a coumarin isolated from the fruits of Tetrapleura tetraptera TAUB (Mimosaceae), have been investigated in vivo and in vitro. The results obtained show that scopoletin inhibits the indirect electrical stimulation-evoked contractions of the cat nictitating membrane (in vivo); and also the contractions of isolated perfused central ear artery of rabbit, induced by electrical stimulation or intraluminal noradrenaline administration. This coumarin, like papaverine, reduces the amplitude and frequency of the spontaneous, myogenic, rhythmic contractions, and exogenous noradrenaline-evoked contractions of the rat isolated portal vein. Scopoletin also inhibits the spontaneous, myogenic, pendular, rhythmic contractions of the rabbit isolated duodenum and attenuates the indirect electrical stimulation-provoked or exogenous noradrenaline-induced relaxations of the muscle preparation. It also depresses the electrical stimulation-evoked contractions of the chick isolated oesophagus. Scopoletin, on its own accord, relaxes all the smooth muscles examined and inhibits the spasmogenic activities of a wide variety of agonists on guinea-pig isolated ileum to approximately the same extent. It is therefore speculated that scopoletin probably produces hypotension in laboratory animals through (a) its smooths muscle relaxant activity - by which means it presumably dilates blood vessels; and (b) by acting as a non-specific spasmolytic agent (like papaverine).