Elevation of the blood pressure is rare in children, occurs occasionally in young adults and appears frequently in elderly persons. Any satisfactory hypothesis of the mechanism of hypertension must necessarily explain the striking variations in the frequency of this disorder at different ages. In the course of an investigation of the possible relation of the renal pressor substance (the renin of Tigerstedt and Bergman1) to certain types of experimental hypertension, we have compared the sensitivity of rats of different ages to this agent. Studies have also been made of the amount of pressor substance in the kidneys of such rats.
Fresh kidneys of hogs were obtained from the slaughter house. The renal cortex was separated from the medulla, passed through a meat grinder and then ground to a fine paste with carborundum. Ninety-five per cent alcohol was then added, in a ratio of 9 cc. to 1 Gm.