Forsberg N E, Baldwin R L, Smith N E
J Dairy Sci. 1985 Oct;68(10):2550-6. doi: 10.3168/jds.S0022-0302(85)81136-X.
Mammary gland tissue slices from three lactating Holstein cows were incubated in Krebs-Ringer bicarbonate-based media with varying concentrations of lactate and other substrates. Conversions of 1- and 2-carbon-14 of lactate to carbon dioxide, fatty acids, citrate, glyceride glycerol, and lactose were determined. Effects of acetate, glucose, beta-hydroxybutyrate, stearate, and pyruvate on lactate metabolism were evaluated. Oxidation of lactate increased asymptotically with lactate concentration. Low acetate concentration stimulated oxidation of carbon 2 of lactate slightly while higher acetate availability inhibited lactate oxidation. Conversion of lactate to fatty acids increased linearly with lactate concentration. This conversion of lactate was inhibited strongly by acetate. Significant conversion of carbon 2 of lactate to glyceride-glycerol but not lactose was detected. Bovine mammary glands have the capacity of utilize sizeable quantities of lactate for oxidation and lipogenesis. Both phenomena are highly dependent on availability of acetate. Pyruvate dehydrogenase and citrate lyase could represent important regulatory sites in vivo for determination of tissue preference for acetate over lactate. Results indicate factors other than an inactive malate transhydrogenation cycle likely limit glucose conversion to fatty acids.
取自三头泌乳期荷斯坦奶牛的乳腺组织切片，在含有不同浓度乳酸及其他底物的基于碳酸氢盐的克氏液中进行孵育。测定了乳酸的1-碳和2-碳-14转化为二氧化碳、脂肪酸、柠檬酸、甘油酯甘油和乳糖的情况。评估了乙酸盐、葡萄糖、β-羟基丁酸盐、硬脂酸盐和丙酮酸盐对乳酸代谢的影响。乳酸的氧化随乳酸浓度呈渐近增加。低浓度乙酸盐略微刺激乳酸2-碳的氧化，而较高的乙酸盐可利用性则抑制乳酸氧化。乳酸向脂肪酸的转化随乳酸浓度呈线性增加。乳酸的这种转化受到乙酸盐的强烈抑制。检测到乳酸的2-碳有显著转化为甘油酯甘油，但未转化为乳糖。牛乳腺有能力利用大量乳酸进行氧化和脂肪生成。这两种现象都高度依赖于乙酸盐的可利用性。丙酮酸脱氢酶和柠檬酸裂解酶可能是体内决定组织对乙酸盐而非乳酸偏好的重要调控位点。结果表明，除了无活性的苹果酸转氢循环外，其他因素可能限制葡萄糖向脂肪酸的转化。
