The action of ephedrine,an alkaloid from Ma Huang.

Abstract

Ma Huang, identified as Ephedra vulgaris var. helvetica, has been known to Chinese medicine since about 3100 B. C., when it was one of the herbs tested and approved by Emperor Shen Nung. According to the Pen Tsao Kang Mu (the Chinese Dispensatory, 1596) it improves circulation, causes sweating, stops cough, reduces fever, etc.

Nagai 1 obtained from the plant an alkaloid which he named ephedrine, and which he 2 found to possess a mydriatic effect. Amatsu and Kubota 3 described a rise in blood pressure and relaxation of the intestines after ephedrine. Merck 4 isolated from the European variety of E. vulgaris an alkaloid named pseudoephedrine isomeric with ephedrine.

In our preliminary investigation an intravenous injection of a simple extract of the crude drug to an anesthetized dog caused a sustained rise in blood pressure, accompanied by prolonged acceleration of heart and constriction of kidney vessels. An alkaloid was soon isolated from the drug and found to have the same effects. This alkaloid has been identified as ephedrine.

The injection of 0.25 to 10 mg. of the alkaloid into a vein of a dog or cat always causes a prolonged rise in blood pressure, cardiac acceleration, and constriction of peripheral vessels. In addition, intestines are relaxed and peristalsis inhibited, uterine tone is increased—these effects are the same in surviving tissues as in those in situ—pupils are widely dilated, and bronchial muscle is relaxed.

After the destruction of the brain and cord the drug acts as before, so that its effects are peripheral. A direct muscle action is eliminated by the tonic action on uterus and blood vessels and inhibitory action on gut and bronchi—effects that point to parasympathetic depression or sympathetic stimulation. That the parasympathetic is not paralyzed is shown by electrical stimulation of the vagus, for the weakest current that slowed the heart continues to be effective during the acceleration produced by ephedrine.