Abstract

1. The blood pressure raising property of ephedrine is not conveniently compared with epinephrine equimolecularly. Suitable doses of ephedrine, however, can make the pressure rise to almost the same level as ordinary doses of epinephrine given to laboratory animals, and maintain it for a much longer time. When mixed with epinephrine, ephedrine shows synergism not only in intensity but in duration.

2. Tyramine, compared with ephedrine, molecule for molecule, raises blood pressure higher but does not maintain a high level as long, when injected intravenously in anesthetized dogs. On repeated injections in stimulating doses, tyramine, when given at intervals of fifteen to twenty minutes does not rapidly lose its effectiveness in raising the blood pressure as ephedrine does. Like ephedrine, tyramine shows synergism with epinephrine both in intensity and duration. In men when given by mouth, tyramine fails to raise blood pressure while ephedrine does.

3. Tyramine, when injected intravenously in anesthetized dogs, increases the heart rate and amplitude of contractions, if the vagi are atropinized, during the rise of blood pressure. Under the same conditions, it increases the cardiac minute output as confirmed by cardiometric and teleroentgenographic studies. Large doses of tyramine also produce a sudden fall of blood pressure, but this fall, unlike ephedrine, is not due to the interference of the automatic and conductive system of the heart as shown by the electrocardiogram, but due to vasodilatation.

4. An explanation based on chemical structure for the difference of chemical stability and persistence of action between tyramine and epinephrine on the one hand and ephedrine on the other, has been offered.