THE EFFECTS OF INTRACISTERNAL INJECTION OF POTASSIUM PHOSPHATE ON THE RATE AND RHYTHM OF THE HEART AND ON THE BLOOD PRESSURE AND ON THE RESPIRATION OF THE DOG

Abstract

Small doses (0.03 ml./kg. body wt.) and large doses (0.12 ml./kg.) of [image] K phosphate were injected into the cisterna magna of dogs. The effects of the soln. in animals after vagotomy, section of the spinal cord at C6 and transection of the brain stem in the inter-collicular region or anterior pontile region were compared with the reactions observed in intact animals. Small doses produced an initial decrease in blood pressure followed by a gradual return to the pre-injn. level. After vagotomy the amt. of fall was diminished and the amt. of rise in blood pressure was augmented. A prompt, marked rise occurred after large doses. An initial decrease in heart rate which persisted was obtained after initial small doses were injected in intact animals. A transient bradycardia followed by a significant increase in heart rate was induced by initial small doses in vagotomized dogs. Large doses usually produced a decrease in heart rate followed by a marked increase which did not persist in intact animals. Bradycardia usually did not occur after large doses in vagotomized dogs. Marked sinus arrhythmias frequently associated with the respiratory cycles were produced after injections in intact animals. Ectopic beats, frank tachycardias and a variety of complexes of abnormal form appeared after injns. in vagotomized animals. The first effect of K phosphate on respiration was an interruption of inspiration which was soon followed by marked stimulation of inspiration. Apneustic respiration usually followed injns. in vagotomized dogs. Marked apneusis was observed after injn. in an animal with the brain stem transected in the anterior pontile region. Observations indicate that on the medullary centers K phosphate produces a direct stimulatory action which activates sympathetic, vagus and respiratory mechanisms.