Laboratory of Veterinary Biochemistry, Department of Veterinary Medicine, Rakuno Gakuen University, Hokkaido 069-8501, Japan.
Laboratory of Meat Science, Department of Food Science and Human Wellness, Rakuno Gakuen University, Hokkaido 069-8501, Japan.
Steroids. 2023 Dec;200:109328. doi: 10.1016/j.steroids.2023.109328. Epub 2023 Oct 18.
Fasting induces metabolic changes in muscles, which are differentiated by muscle fiber type. In this study, the mechanism of fasting-induced muscle atrophy in rats was examined to determine the differences between muscle fiber types in energy production. Fasting for 96 h did not alter the weight of the soleus (SOL), a fiber type I muscle, but did significantly reduce the weight of gastrocnemius (GM), a fiber type II muscle. GM, SOL and blood pregnenolone and testosterone levels decreased under fasting, which induced energy deprivation, whereas corticosterone (CORT) levels significantly increased. However, the expression of 3β-HSD and P45011β in GM was unaffected by fasting. The decrease in GM weight may be due to decreased levels of testosterone and reduced synthesis of mammalian target of rapamycin (mTOR). Significant increases in CORT both GM and SOL were associated with increases in the amount of branched-chain amino acids available for energy production. However, decreased levels of mTOR and IGF1 and increased levels of CORT and IL-6 in SOL suggest that GM proteolysis was followed by SOL proteolysis for additional energy production. In conclusion, IGF1 levels decreased significantly in SOL, whereas those of IL-6 significantly increased in SOL and blood but decreased in GM. Blood branched-chain amino acids (BCAA) levels were unaffected due to fasting, whereas an increase was noted in the levels of BCAA in GM and SOL. These results show that fasting for 96 h restricts energy supply, producing fast-twitch muscle atrophy followed by slow-twitch muscle atrophy.
禁食会引起肌肉代谢变化，这些变化因肌肉纤维类型而异。在这项研究中，检查了禁食引起大鼠肌肉萎缩的机制，以确定不同肌肉纤维类型在能量产生方面的差异。禁食 96 小时不会改变Ⅰ型纤维的比目鱼肌（SOL）的重量，但会显著降低Ⅱ型纤维的腓肠肌（GM）的重量。GM、SOL 和血液中的孕烯醇酮和睾丸酮水平在禁食时下降，导致能量匮乏，而皮质酮（CORT）水平显著升高。然而，GM 中的 3β-HSD 和 P45011β 的表达不受禁食影响。GM 重量的下降可能是由于睾丸酮水平降低和哺乳动物雷帕霉素靶蛋白（mTOR）合成减少所致。GM 和 SOL 中 CORT 的显著增加与可用于能量产生的支链氨基酸（BCAA）的增加有关。然而，SOL 中 mTOR 和 IGF1 水平降低以及 CORT 和 IL-6 水平升高表明，GM 蛋白水解后 SOL 也进行了蛋白水解以获取额外的能量。总之，SOL 中的 IGF1 水平显著降低，而 SOL 和血液中的 IL-6 水平显著升高，但 GM 中的 IGF1 水平降低。由于禁食，血液中支链氨基酸（BCAA）水平不受影响，但 GM 和 SOL 中 BCAA 水平升高。这些结果表明，禁食 96 小时会限制能量供应，导致快肌萎缩，随后是慢肌萎缩。
