Effects of insulin and of glycerol in vitro on the incorporation of [carboxy-14C]acetate into the fatty acids of lactating mammary gland slices with special reference to species differences

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Abstract
Rat mammary gland slices incorporated no acetate C into the fatty acids in acetate alone, but incorporated considerable amts. in the presence of glucose. Sheep udder slices effected considerable fatty acid synthesis from acetate alone, but the utilization of acetate C for this purpose was greatly increased in presence of glucose. Insulin did not alter the inactivity of rat mammary gland slices towards acetate as sole substrate, but in presence of glucose it considerably increased the C14 found in the fatty acids. The incorporation of C14 into the fatty acids of sheep udder slices was unaffected by insulin both in acetate alone and in acetate plus glucose. Glycerol caused a slight incorporation of acetate C into the fatty acids of rat mammary gland slices in acetate alone, and in acetate plus glucose its stimulating effect on C14 incorporation was as great as that of insulin. It stimulated the utilization of acetate for fatty acid synthesis by sheep udder slices in acetate alone but in acetate plus glucose its effect was slightly inhibitory. Glyceride glycerol isolated as tri-p-nitrobenzoate from the neutral fat of the slices was not radioactive in any expt. Mammary gland slices uner the exptl. conditions did not incorporate acetate C into glycerol. Deductions from respiratory and acid-change measurements as to the ability of mammary gland slices to utilize acetate for fatty acid synthesis in vitro and the effect of glucose, of insulin and of glycerol upon this process in ruminant and nonruminant mammary tissue,respectively, were confirmed.