Changes in the arginase and alkaline phosphatase contents of the mammary gland and liver of the rat during pregnancy, lactation and mammary involution

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Abstract
Changes in the mammary gland and liver arginase, and the mammary gland and kidney alkaline phosphatase, were studied in pregnancy, lactation, and mammary involution in the rat. Retained milk in mammary gland tissue was estimated by determining lactose in the gland homogenates and this used to correct the mammary gland enzyme detns. to a true moist tissue basis. The liver arginase content (/g. moist tissue) during pregnancy and after weaning was indistinguishable from that of unmated controls except at the 15th day of pregnancy when significantly lower values were observed. Over the whole lactation period, the liver arginase was significantly increased above those values. The mammary gland arginase increased slowly during pregnancy and early lactation but underwent a dramatic increase between the 5th and 10th days of lactation. It reached a maximum at the 20th day of lactation and after weaning fell precipitously to the level of early pregnancy. The alkaline phosphatase content in the mammary gland increased rapidly during pregnancy, reaching a maximum at parturition, and remaining at the same level throughout lactation; it decreased after weaning to a level intermediate between those of lactation and early pregnancy. The alkaline phosphatase content of kidney tissue remained constant throughout pregnancy, lactation, and mammary involution. The results were believed to indicate that the mammary gland arginase was concerned with the deamination of amino-acids by the mammary gland, and that the increased arginase content during late lactation in the rat was due to an increased requirement of deaminized residues for the synthesis of milk constituents. The results were consistent with the view that the alkaline phosphatase of the mammary gland might be concerned with the synthesis of nucleo-proteins during the growth phase and possibly with the synthesis of casein and the capture of blood sugar molecules during lactation. During lactation in the rat, kidney tissue contained on the avg. 2-9 times as much alkaline phosphatase as mammary gland tissue. During the mammary growth phase, i.e. in early pregnancy, the kidney/mammary gland ratio was approx. 34.