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

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Abstract
In 17 perfusions of bovine mammary glands, for 4-5 hrs., 10 were conducted with normal blood glucose levels, to 5 of which 160 units of insulin were added, and, in 7, large excesses of blood glucose were maintained and 120 to 160 units of insulin were added. Milk was withdrawn at 1 or 2-hr. intervals for lactose detn. and glycogen was detd. in the non-perfused half at the beginning and in the perfused glands at the end of the expts. With insulin admn. the lactose dropped progressively with each successive milking from 4.1% at the beginning to as low as 0.49% at the end of 5 hrs. of perfusion. In the non-insulinized glands the values were 3.77 and 2.84%, respectively, for the beginning and 5 hrs. of perfusion. Insulin caused an increase in tissue glycogen. Insulin appears to block glycogen degradation rather than stimulate its formation; lactose is probably formed from glycogen degradation.

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