THE ACTION OF EPHEDRINE, THE ACTIVE PRINCIPLE OF THE CHINESE DRUG MA HUANG

1. Ma Huang—Ephedra Vulgaris var. helvetica—contains an alkaloid which is its active principle. This alkaloid is identical with ephedrine and isomeric with pseudoephedrine. 2. The physiological effects of ephedrine are very similar to those of epinephrine but are much more prolonged. All of its effects are comparable to those of sympathetic stimulation. 3. The outstanding effect of ephedrine is circulatory stimulation, which is due largely to stimulation of the cardiac accelerator mechanism, exerted simultaneously on ganglia and endings. Large doses depress heart muscle and cause a fall in blood pressure. Constriction also occurs in blood vessels supplied with vasoconstrictor nerves, and is more marked in the splanchnic area than in a limb. Maximal cardiac effects are elicited before vasoconstriction is marked, and subsequent doses cause further constriction until a maximum is reached, beyond which further doses depress the heart muscle and lower blood pressure. In man vasoconstriction is apparently more prominent, for pulse rate is always decreased as blood pressure rises. 4. The other effects are analogous to those of epinephrine: the intestine is inhibited and relaxed, the uterus is stimulated, the bronchi are dilated and mydriasis occurs after local or systemic exhibition of ephedrine; salivary secretion is sometimes increased by ephedrine after atropine, but there is no definite effect on secretion of sweat; diuresis occurs after the vasoconstrictor effect diminishes due apparently to more prolonged effects on heart than on vessels and possibly also to irritation of the kidney by the drug. 5. Ephedrine is not very toxic, the minimum fatal dose being 100 to 145 mgm. per kilo in rats, death following convulsions. Smaller doses are apparently harmless, though repeated intravenous injections of large doses produced kidney degeneration in a rabbit. 6. The drug is effectively absorbed from the intestines or following subcutaneous or intramuscular injection. Its solutions are stable indefinitely when exposed to light and air and are not decomposed by boiling. 7. Ephedrine has been tried clinically as a circulatory stimulant, with favorable results. A patient with Addison's disease has been markedly improved by it. Its efficiency as a bronchodilator has not been tested. Its mydriatic effects are of the cocaine order, but are more intense than those of cocaine. 8. Should ephedrine prove valuable clinically, its advantages over epinephrine lie in the greater persistence of ephedrine effects, the greater stability of its solutions, and the possibility of securing effects when the drug is given by mouth.