A R T E R I a L H Y P E R T E N S I O N I N Rats I. Methods

The blood pressure of anesthetized rats has been measured in the course of several experiments. Attempts were made to produce arterial hypertension x by a number of methods. These investigations were undertaken in order: (1) to learn what the normal blood pressure of rats is under anesthesia, (2) to develop methods to bring about arterial hypertension, (3) to study some of the pathological changes in animals when chronic arterial hypertension has persisted, and (4) to provide preparations for ascertaining the action of pressor and depressor substances. Methods Three hundred and fifty adult Norwegian white rats were used. Most were males. Blood pressures were measured with Hamilton's optical manometer, 5 per cent sodium citrate being used as an anticoagulant. All animals were anesthetized by intraperitoneal injection of pentobarbital sodium (4.5 rag. per 100 gin. body weight). The right femoral artery was exposed, and a strong solution of novocaine applied to it to prevent contraction. A curved 23 gauge needle connected to the manometer was inserted into the artery through a small incision. Heparin was injected intravenously when continuous tracings ~vere to be taken. Operations on the kidneys were performed under ether anesthesia, as the use of pentobarbital sodium resulted in many deaths owing to strangulation from obstruction of the upper respiratory passages. The disadvantages of this method for measuring blood pressure are" (1) animals are anesthetized and are, therefore, not under normal conditions, (2) only two or possibly three measurements can be made at different times on each animal, and (3) the rate of mortality from anesthesia alone is high (roughly 20 per cent). There are, however, several advantages: continuous records of the blood pressure can be made for as long as 2 hours, the blood pressure is probably at basal levels, and both systolic and diastolic pressures are measured with a considerable degree of accuracy. x The term arterial hypertension, in this study, is intended to mean a vascular disease of rats, of which one manifestation is elevation of blood pressure.