Relative utilization of glucose and acetate carbon for lipogenesis by mammary-gland slices, studied with tritium, 13C and 14C

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Abstract
When incubated in a medium containing [C14] glucose plus [carboxy-C13-Me-H3] acetate, mammary-gland slices from lactating rats incorporate into the fatty acids about 8 times more glucose C and about 6 times less acetate C than slices from lactating ewes. Mammary tissue from the rat utilizes C from acetate or glucose for fatty acid synthesis at approx. equal rates, while udder slices from the ewe utilize for this purpose in a given time about 30 times more acetate C than glucose C In the presence of acetate plus glucose, rat-mammary slices utilize less glucose C for fatty acid synthesis than in the presence of glucose alone. Acetate has no effect on the trivial utilization for fatty acid synthesis of glucose C by slices of sheep udder. Insulin, added in vitro, increases incorporation of glucose and acetate C into the fatty acids of rat-mammary slices to about the same extent; glycerol increases utilization of acetate C significantly more than that of glucose C. Both rat and sheep mammary tissue utilize both C atoms of acetate for lipogenesis to an equal extent. There is no evidence that the 2 C chain is split in the course of lipogenesis. About 2/3 of the H atoms of acetate are lost or exchanged during chain elongation.