The Existence of Two Forms of Hypertensin

Abstract

The pressor substance hypertensin, which is the product of the action of the renal enzyme renin upon its plasma substrate, has been shown to be present in the arterial blood of many patients with hypertensive cardiovascular disease (1) as well as in the arterial blood of animals with experimental renal hypertension (2--4). Hypertensin may, therefore, be concerned in causing the elevation of blood pressure in both of these conditions. In the course of attempts to purify this material it was found that certain preparations, when examined by means of the countercurrent distribution method, revealed not one but two pressor substances. Further study of this completely unexpected finding showed that the initial pressor substance, hypertensin I, formed as a result of the action of renin on its substrate, is quickly converted to a second substance with approximately equal pressor activity, hypertensin II, apparently by an enzyme in plasma, which is activated by chloride ion. I t is the purpose of this paper to describe the preparation of hypertensin I from suitable preparations of renin and substrate, to demonstrate its conversion to hypertensin I I by the action of the plasma enzyme, and to determine which ions are effective in activating this enzyme. MetkodsPreparation of Renin.--The renin was prepared from fresh hog kidneys according to the method described by Katz and Goldblatt (5) and modified by Dexter (6). Tiffs preparation contained a considerable amount of hypertensinase activity which was eliminated (reference 7, page 101) in the following fashion. Renin, prepared from 100 pounds of hog kidneys by ammonium sulfate precipitation, was dissolved in 1.5 liters of water. The solution was chilled to 0-5°C. and sufficient solid sodium chloride was added to insure complete saturation. 0.1 N HCI, saturated with NaC1, wa~nthen dripped into the solution slowly and with constant stirring until the pH dropped to 2.0. The solution was centrifuged at high speed at 0-5°C. The supernatant containing the hypertensinase was decanted and discarded. The precipitate was dissolved in 1 liter of cold 0.1 ~ Na,I-IPO4. The light brown solution was adjusted to pH 7.5, put into small diameter cellophane bags, and dialyzed exhaustively against cold distilled water. The resulting product, with a volume of about 1.25 liters, was found to be uniformly free of hypertensinase. Usually 1 volume of this enzyme preparation was adequate to catalyze the formation of hypertensin in 25 volumes of the substrate preparation described below in a period of 30 to 45 minutes when this mixture was incubated at 37°C. and pH 7.5.Preparation of Substrate.--Horse blood was collected in ~0 volume of 4 per cent sodium

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