Damon M, Louveau I, Lefaucheur L, Lebret B, Vincent A, Leroy P, Sanchez M P, Herpin P, Gondret F
Unité Mixte de Recherches Systèmes d'Elevage Nutrition Animale et Humaine, Institut National de la Recherche Agronomique, 35590 Saint Gilles, France.
J Anim Sci. 2006 May;84(5):1083-92. doi: 10.2527/2006.8451083x.
Intramuscular fat content is generally associated with improved sensory quality and better acceptability of fresh pork. However, conclusive evidence is still lacking for the biological mechanisms underlying i.m. fat content variability in pigs. The current study aimed to determine whether variations in i.m. fat content of longissimus muscle are related to i.m. adipocyte cellularity, lipid metabolism, or contractile properties of the whole muscle. To this end, crossbred (Large White x Duroc) pigs exhibiting either a high (2.82 +/- 0.38%, HF) or a low (1.15 +/- 0.14%, LF) lipid content in LM biopsies at 70 kg of BW were further studied at 107 +/- 7 kg of BW. Animals grew at the same rate, but HF pigs at slaughter presented fatter carcasses than LF pigs (P = 0.04). The differences in i.m. fat content between the 2 groups were mostly explained by variation in i.m. adipocyte number (+127% in HF compared with LF groups, P = 0.005). Less difference (+13% in HF compared with LF groups, P = 0.057) was noted in adipocyte diameter, and no significant variation was detected in whole-muscle lipogenic enzyme activities (acetyl-CoA carboxylase, P = 0.9; malic enzyme, P = 0.35; glucose-6-phosphate dehydrogenase, P = 0.75), mRNA levels of sterol-regulatory element binding protein-1 (P = 0.6), or diacylglycerol acyltransferase 1 (P = 0.6). Adipocyte fatty acid binding protein (FABP)-4 protein content in whole LM was 2-fold greater in HF pigs than in LF pigs (P = 0.05), and positive correlation coefficients were found between the FABP-4 protein level and adipocyte number (R2 = 0.47, P = 0.02) and lipid content (R2 = 0.58, P = 0.004). Conversely, there was no difference between groups relative to FABP-3 mRNA (P = 0.46) or protein (P = 0.56) levels, oxidative enzymatic activities (citrate synthase, P = 0.9; beta-hydroxyacyl-CoA dehydrogenase, P = 0.7), mitochondrial (P = 0.5) and peroxisomal (P = 0.12) oxidation rates of oleate, mRNA levels of genes involved in fatty acid oxidation (carnitine-palmitoyl-transferase 1, P = 0.98; peroxisome proliferator-activated receptor delta, P = 0.73) or energy expenditure (uncoupling protein 2, P = 0.92; uncoupling protein 3, P = 0.84), or myosin heavy-chain mRNA proportions (P > 0.49). The current study suggests that FABP-4 protein content may be a valuable marker of lipid accretion in LM and that i.m. fat content and myofiber type composition can be manipulated independently.
肌内脂肪含量通常与鲜猪肉更好的感官品质和可接受性相关。然而，关于猪肌内脂肪含量变异的生物学机制仍缺乏确凿证据。本研究旨在确定背最长肌肌内脂肪含量的变化是否与肌内脂肪细胞的细胞构成、脂质代谢或整块肌肉的收缩特性有关。为此，选取体重70千克时背最长肌活检显示脂质含量高（2.82±0.38%，HF）或低（1.15±0.14%，LF）的杂交（大白猪×杜洛克猪）猪，在体重107±7千克时进一步研究。动物生长速度相同，但屠宰时HF猪的胴体比LF猪更肥（P = 0.04）。两组间肌内脂肪含量的差异主要由肌内脂肪细胞数量的变化解释（HF组比LF组增加127%，P = 0.005）。脂肪细胞直径差异较小（HF组比LF组增加13%，P = 0.057），整块肌肉的生脂酶活性（乙酰辅酶A羧化酶，P = 0.9；苹果酸酶，P = 0.35；葡萄糖-6-磷酸脱氢酶，P = 0.75）、固醇调节元件结合蛋白-1的mRNA水平（P = 0.6）或二酰基甘油酰基转移酶1的mRNA水平（P = 0.6）均未检测到显著变化。HF猪背最长肌中脂肪细胞脂肪酸结合蛋白（FABP）-4蛋白含量比LF猪高2倍（P = 0.05），且FABP-4蛋白水平与脂肪细胞数量（R2 = 0.47，P = 0.02）和脂质含量（R2 = 0.58，P = 0.004）呈正相关。相反，两组间FABP-3的mRNA（P = 0.46）或蛋白（P = 0.56）水平、氧化酶活性（柠檬酸合酶，P = 0.9；β-羟酰基辅酶A脱氢酶，P = 0.7）、油酸的线粒体（P = 0.5）和过氧化物酶体（P = 0.12）氧化速率、参与脂肪酸氧化的基因的mRNA水平（肉碱-棕榈酰转移酶1，P = 0.98；过氧化物酶体增殖物激活受体δ，P = 0.73）或能量消耗（解偶联蛋白2，P = 0.92；解偶联蛋白3，P = 0.84）或肌球蛋白重链mRNA比例（P>0.49）均无差异。本研究表明，FABP-4蛋白含量可能是背最长肌脂质蓄积的一个有价值的标志物，且肌内脂肪含量和肌纤维类型组成可独立调控。
