SOME CIRCULATORY PHENOMENA DISCLOSED BY ERGOTOXINE

Abstract

After a moderate dose of ergotoxine a dose of adrenin, which gives an almost pure rise of blood pressure in the whole animal produces a pure fall if the circulatory area is limited by clamping the aorta at the diaphragm. This difference in effect does not depend on the original blood-pressure level. From this fact and other evidence previously reported, the inference is drawn that the splanch-nics have primarily vasoconstrictor action and that probably sympathetic vasodilators are distributed mainly to skeletal muscle. The bearing of this selective distribution on the theory of transmission of the sympathetic nerve impulses to the effectors, recently developed by Cannon and Rosenblueth is discussed. In the spinal animal ergotoxine causes a rise of blood pressure, whereas in the myelencephalic preparation ergotoxine produces a considerable fall. This difference is explained by the excitation of a dilator center in the medulla by ergotoxine. Although most vasomotor reflexes are readily abolished by ergotoxine, some persist after doses of ergotoxine sufficient to transform the blood pressure response to adrenin into a pure fall. The cardiac reflexes persist, modified by the central and peripheral effects of ergotoxine on the vagi. Some of the motor effects elicited by ergotoxine in different preparations are described. The most noticeable characteristic seems to be a marked reflex hyperexcitability of all motor centers. Muscular activity lowers the blood pressure of ergotoxinized animals. Injection of curare, on the contrary, is followed by a rise.