A Simple Method for the Bioassay of Renin

Abstract

In connection with work on hypertension it was of importance to have a simple method for testing a large number of extracts for their renin content. Rabbits were used for the test as their blood pressure is conveniently measured in the artery of the ear by a membrane manometer. 1

After several preliminary trials a procedure was standardized, which, despite its simplicity gives reliable and reproducible results, as accurate as one would expect from a bioassay.

The test was carried out in a warm room. The unanesthetized animals were placed in a box with open front and top; after some training they would sit quietly. The left ear was placed between the capsule and light of the manometer without forcing it away from its natural position. Measurements of the blood pressure were taken at about 1/2-minute intervals; after a few minutes the readings were constant, fluctuating not more than one millimeter from the average level. After a constant level had been maintained for at least 3 minutes, the extract was injected intravenously in the right ear. The introduction of the needle had no effect on the blood pressure, as the right ear had previously been denervated. Injection of 5 cc of physiological saline solution also had no effect on the blood pressure.

The injection time chosen was 60 seconds, but practically the same results were obtained if the injection was made in 30 seconds. When the injection was started, measurements of the blood pressure were done in rapid succession, about 3 per minute. The maximum response to renin was usually obtained about 3 minutes after the start of the injection. For each extract 4 animals were used and amounts of renin were injected which would cause a rise in blood pressure of 20 to 40 mm mercury.