Abstract
It has been pointed out by one of us 1 that pitressin (Vaso-pressin) caused a marked drop in blood pressure and decreased pulse rate in the unanesthetized dog. The decreased pulse rate we then believed to be of vagal origin. The present work is a continuation of these earlier experiments.
The effect of the drug upon the heart was noted by recording the electrical potential changes in the action current by the string galvanometer in leads I and III, although usually only the latter lead was employed. Unanesthetized dogs were used. The pitressin was injected intravenously in small doses 0.1 to 0.5 cc. and in some cases followed by the injection of atropine sulphate in doses of 0.2 mgm. or more per kilo. In other experiments the atropine was injected intravenously before the pitressin and other experiments were performed on animals in which the vagi had been severed under ether anesthesia a sufficient time earlier for the animals to have recovered.
In a series of unanesthetized dogs the effect of pitressin upon the blood pressure and pulse rate was studied by means either of a mercury monometer or of a membrane monometer. The pulse rate was counted before, during and following the fall in blood pressure. Other conditions were similar to the above described experiments.
The effect of pitressin upon coronary flow was studied in excised perfused rabbit's hearts.
Results. The electrocardiographic studies in the normal unanesthetized dog shows the heart slowed, 10 to 15 seconds after the injection of pitressin. This slowing was quickly followed by an acceleration which was subsequently followed by marked slowing of the heart, which persisted for several minutes. During the period of excessive slowing high branching of the T-wave occurred with a marked increase in the height of the wave.
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