The effect of glucose and acetate on milk secretion by the perfused goat udder

Abstract

The influence of acetate and glucose on the respiration and milk production and composition has been studied in isolated goat udders perfused with simplified medium and receiving adequate calories, amino acids and minerals. In glands receiving glucose plus acetate the oxygen uptake and respiratory quotients were similar to those of udders of conscious goats in declining lactation, and milk, of reasonably normal composition, was secreted for 12 hr. at about 50% of the level before the experiment. Glands given glucose only had a lower oxygen uptake, and R.Q. < 1, and the milk yield was slightly reduced to about 40% of the previous level. Milk fat concentration fell to < 20% of the level observed in milk secreted before the experiment. With acetate only, the oxygen uptake was equal to that with glucose but the respiratory quotients was higher than that observed with glucose plus acetate. However, milk secretion fell to very low levels and was restored by adding glucose. Milk secretion was not stimulated in glands receiving mainly acetate by adding small quantities of glucose or fumarate. Our results confirm that acetate and glucose are used to form milk fat and lactose respectively, but show in addition that glucose is essential for the secretion of fluid. It is suggested that the secretions of fluid, lactose, protein and fat are to some extent independent processes. The relationship of these findings to the pathways of glucose metabolism is discussed.