ELECTROCARDIOGRAPHIC AND BLOOD PRESSURE CHANGES INDUCED BY POSTERIOR PITUITARY EXTRACT (POSTLOBIN-V), AND THE INFLUENCE OF EPHEDRINE THEREUPON

¹ Department of Pharmacology, McGill University, Montreal, Canada

1. Simultaneous blood pressure and electrocardiographic changes following injections of large doses of postlobin-V have been studied in chloretonized and unanesthetized dogs with and without the vagi cut.

2. It can be shown that associated with the fall in blood pressure thus observed, there are characteristic alterations in the T-wave of the electrocardiogram and some cardiac slowing. After vagus section the P-wave is additionally reversed. The appearance of these effects may be prevented by administration of ephedrine.

3. The rôle of reflex vagus control in connection with these phenomena is discussed.

4. It is concluded that the changes in T-wave produced by postlobin-V represent ventricular effects resulting from anoxemia secondary to coronary constriction which would also appear to be responsible for both the slowing and P-wave changes, possibly from some effect upon A-V node function due to the same factors (since both are abolished by ephedrine).

5. The data suggest further that postlobin-V exerts no primary effect upon the myocardium or conducting mechanism of the heart even in the high dosages employed, but that the above described effects (apart from vagal reflex effect) are all secondary to its coronary constricting action.