Vitamin A and its metabolite, retinoic acid (RA) play important roles in regulating skeletal muscle development. This study was conducted to investigate the effects of early intramuscular vitamin A injection on the muscle growth of lambs. A total of 16 newborn lambs were given weekly intramuscular injections of corn oil (control group, n = 8) or 7,500 IU vitamin A palmitate (vitamin A group, n = 8) from birth to 3 wk of age (4 shots in total). At 3 wk of age and weaning, biceps femoris muscle samples were taken to analyze the effects of vitamin A on the myogenic capacity of skeletal muscle cells. All lambs were slaughtered at 8 months of age. The results suggest that vitamin A treatment accelerated the growth rate of lambs and increased the loin eye area (P < 0.05). Consistently, vitamin A increased the diameter of myofibers in longissimus thoracis muscle (P < 0.01) and increased the final body weight of lambs (P < 0.05). Vitamin A injection did not change the protein kinase B/mammalian target of rapamycin and myostatin signaling (P > 0.05). Moreover, vitamin A upregulated the expression of PAX7 (P < 0.05) and the myogenic marker genes including MYOD and MYOG (P < 0.01). The skeletal muscle-derived mononuclear cells from vitamin A-treated lambs showed higher expression of myogenic genes (P < 0.05) and formed more myotubes (P < 0.01) when myogenic differentiation was induced in vitro. In addition, in vitro analysis showed that RA promoted myogenic differentiation of the skeletal muscle-derived mononuclear cells in the first 3 d (P < 0.05) but not at the later stage (P > 0.05) as evidenced by myogenic gene expression and fusion index. Taken together, neonatal intramuscular vitamin A injection promotes lamb muscle growth by promoting the myogenic potential of satellite cells.

维生素 A 及其代谢物视黄酸 (RA) 在调节骨骼肌发育中发挥着重要作用。本研究旨在探讨早期肌肉注射维生素A对羔羊肌肉生长的影响。 16只新生羔羊从出生到3周龄每周肌注玉米油（对照组，n  = 8）或7,500 IU维生素A棕榈酸酯（维生素A组，n = 8）（共注射4次） 。3周龄和断奶时，采集股二头肌样本，分析维生素A对骨骼肌细胞生肌能力的影响。所有羔羊均在 8 个月大时宰杀。结果表明，维生素A处理加速了羔羊的生长速度，增加了腰眼面积（P  <0.05）。一致的是，维生素A增加了胸最长肌的肌纤维直径（P  <0.01）并增加了羔羊的最终体重（P  <0.05）。维生素 A 注射未改变雷帕霉素和肌肉生长抑制素信号传导的蛋白激酶 B/哺乳动物靶点（P  > 0.05）。此外，维生素A上调PAX7（P <0.05）和包括MYOD和MYOG 在内的生肌标记基因（P  <0.01）的表达。维生素A处理的羔羊骨骼肌来源的单核细胞 在体外诱导肌源性分化时，肌源性基因表达较高（ P  <0.05），并形成更多的肌管（P <0.01）。此外，体外分析显示，肌源性基因 表达和融合指数表明， RA在前3 d促进骨骼肌源性单核细胞的肌源性分化（ P  < 0.05），但在后期则不促进骨骼肌源性单核细胞的肌源性分化（P > 0.05）。 。综上所述，新生儿肌肉注射维生素 A 可以通过促进卫星细胞的生肌潜力来促进羔羊肌肉的生长。