Pharmacological studies on coleonol, a hypotensive diterpene from Coleus forskohlii.

Coleus spp. have been used in Aurvedic medicine for heart diseases, spasmodic pain, painful micturition and convulsions. The pharmacological properties of coleonol, a diterpene, isolated from Coleus forskohlii were investigated. Its predominant effect is to lower the blood pressure of anaesthetised cat and rat as well as of the spontaneously hypertensive rat due to relaxation of the vascular smooth muscle. In small doses it has a positive inotropic effect on isolated rabbit heart as well as on cat heart in vivo. Coleonol also exhibits nonspecific spasmolytic activity on smooth muscle of the gastrointestinal tract in various species but not on bronchial musculature of guinea pig. Large doses of coleonol have a depressant action on the central nervous system. These results provide the rationale for the use of this plant in Aurvedic medicine.