Ether anesthesia has a marked influence in diminishing the pressor response to minute amounts of epinephrine injected directly into the circulation. Hemorrhage also acts to lessen or abolish the response, and to a degree directly proportional to the lowering of the blood pressure it causes. In the exsanguinated animal an amount of epinephrine three or four times that sufficient to produce a pressure rise of 10 to 15 mm. of mercury under normal conditions, may be entirely without effect. The response to large doses, on the other hand, is uninfluenced by ether or hemorrhage.
The facts stated have a practical bearing not only on the employment of epinephrine to tide over collapse but on its possible utilization in the future to raise a low blood pressure to the normal height and maintain it during a considerable period. For the amount of epinephrine which under normal conditions will suffice to bring up the blood pressure may have little or no effect on an etherized individual or on one who has lost blood. The same difficulty will doubtless be encountered under other conditions.
In animals rendered plethoric by transfusion the response to small doses of epinephrine lessens in proportion as the blood pressure is increased by the plethora.