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Studies of the Carbohydrate Metabolism of Mammary Gland Tissue in Vitro. III. Glycogen as an Intermediary in the Formation of Lactose¹

University of Minnesota, St. Paul, Minnesota

ABSTRACT

Although the mammary gland has been shown to take up the carbohydrate portion of glycoproteins (17), to use lactic acid under certain conditions (6, 15) and to form lactose from glucose, maltose and glycogen in in vitro experiments (10, 11), blood glucose is considered to be the chief precursor of milk sugar (2, 7, 8, 9, 13, 19). The reduced milk secretion and lactose concentration following insulin administration (3, 5, 14) has been attributed to the resulting hypoglycemia suggesting that glucose is directly converted into the milk sugar in the mammary gland.

Reports by Petersen et al. (15) that lactating glands contain relatively large amounts, and non-active glands small amounts of glycogen raises the question of the rôle played by this substance in lactose synthesis. Demonstrations by Knodt and Petersen (12) that glycogen can be converted into lactose, suggest the possibility of the various blood precursors being first converted into glycogen but does not prove the point as the glycogen might serve merely as a carbohydrate reservoir to be drawn upon in case of inadequate blood precursors.

¹ Taken from data presented in a thesis to graduate faculty of the University of Minnesota by C. B. Knodt in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Scientific Journal Series Paper No. 2255, Minnesota Agricultural Experiment Station.