Positive inotropic and blood pressure lowering activity of a diterpene derivative isolated from Coleus forskohli: Forskolin.

Forskolin is a diterpene derivative isolated from the Indian plant Coleus forskohli. Forskolin has positive inotropic action on the isolated guinea pig heart, on the isolated left atrium of the guinea pig heart and on the dog and cat heart in situ. It increases the heart rate. The positive inotropic effect on the increase of heart rate are not blocked by beta-blockers. On reserpinized dogs the actions on the heart could also be seen. With high doses the action potential of the guinea pig papillary muscle is shortened. The positive inotropic effect could be differentiated from the effects of theophylline, cardiac glycosides and veratrine. Forskolin lowers the blood pressure in dogs and cats and also in spontaneously hypertensive and renal hypertensive rats.