Studies on the metabolism of mammary tissue in vitro. 2. Oxidation of acetate and glucose by slices of lactating sheep mammary gland

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Abstract
The rates of oxidation of the 2 C atoms of sodium acetate, glucose total carbon and the C(1) atom of glucose were measured in lactating-sheep mammary slices in the presence and absence of other substrates. The rates of oxidation of the 2 acetate C atoms are increased by about 50% on addition of glucose to the medium, the ratio of their rates of oxidation being unaffected. Pyruvate causes a reduction in the rate of acetate oxidation and an increase in the ratio of the rates of oxidation of the 2 carbon atoms (qco2H/Me). The formula of Strisower et al. (1952) applied to these results indicates that whereas pyruvate can give rise to tricarboxylic acid cycle intermediates, glucose cannot and suggests a metabolic block between glucose and pyruvate in this tissue. Studies on the oxidation of glucose in the presence and absence of pyruvate, neither confirm this conclusion nor indicate that the direct oxidative pathway is a major route of glucose catabolism. The effect of acetate on glucose oxidation was investigated and found to increase it threefold, glucose and acetate thus increasing the rate of oxidation of each other. The metabolic behavior of sheep mammary tissue is com-pared with that of rat mammary tissue previously reported.