Arginase in the Mammary Gland

Abstract

The liver has been considered as the only gland in the mammalian body capable of synthesizing urea. Hunter and Daupinee 1 reported that the liver contained large quantities of arginase which has not been reported for other glands in the mammalian body. Krebs and Henseleit 2 advanced the generally accepted hypothesis that arginase is one of the essentials in the formation of urea.

Since urea has been reported to be produced by the mammary gland by Graham, Houchin and Turner, 3 it appeared probable that the method of formation was similar to that in the liver and that arginase may be present in the mammary gland.

Accordingly, both lactating and non-lactating mammary glands from cows were analyzed for arginase by the method described by Hunter and Daupinee. 4 In each case 100 g of udder tissue were extracted with 100 ml of 75% glycerol. For the trials 5 ml of the glycerol extract were added to the arginine solution and the urea formed after 24 hours of incubation was determined by the urease method of Van Slyke and Cullen. 5 Blanks were run identically with the exception that arginine was omitted. The urea nitrogen in the blanks varied from 0.0 mg in the case of the dry glands to as much as 0.43 mg in the case of lactating glands. The amounts of urea nitrogen from 5 ml of glycerol extract as compared to 5 ml of glycerol extract and arginine hydrochloride are given in Table I.

From these data it is obvious that the active mammary gland contains appreciable arginase while the inactive gland contains less or none at all as revealed by the methods used.

It will be noted in the table that the amount of arginase in the mammary gland extract is proportional to the amount of preformed urea in the mammary gland extract, as shown by the blank determinations. This urea was probably formed in the gland or gland extract by arginase and urea precursors in the gland. Additional controls demonstrated that the arginine used did not contain free urea.