Effect Of Low Protein Diet Supplemented With Individual Essential Amino Acid On Skeletal Muscle Protein Synthesis In Growing Rats

Amino acids can affect protein synthesis through signaling.Studies in lactating animals have shown that a single essential amino acid has different effects on the mammalian rapamycin target protein complex 1(mTORC1)signaling pathway,and therefore has different effects on milk protein synthesis.The differences in the single essential amino acid affecting the mTORC1 signaling pathway have not been studied in growing animal systems.In view of the economic difficulties of carrying out this research in growing ruminants,this project uses model animal growth rats as experimental animals to observe single essential amino acids effect on the mTORC1 signaling pathway and growth performance of muscle tissue.1.Growth rate-protein intake response curve: To obtain the rat growth rate-protein intake response curve,in the range of 2% to 26%,7 different crude protein(CP)levels were designed in 4% steps.Diets were used to determine the growth rate and protein intake of rats.To reduce the effect of energy intake differences,non-protein intake of energy was used as a fixed effect,and the curve was obtained by data fitting.The dietary protein level of the positive control group was determined to be 18% by the US AIN-93 G standard,and the dietary protein level when the weight gain of the positive control group was significantly different from the positive control group(P<0.05)of 6%.The experimental high-protein control diet and the low-protein supplemented single essential amino acid diet.2.Low protein diet added single essential amino acid test: 18%(HP)and 6%(LP)CP diet were used as positive and negative controls,respectively.The experimental treatment was LP+ single essential amino acid,a total of 12 test groups.The amount of single essential amino acid added is based on casein.The content of this essential amino acid in the diet of HP and LP is different.The amount of each essential amino acid is between 1.52 and 11.0 g / kgdry matter.The CP level of the diet after adding is 6.15.% ~ 7.10%.Compared with the negative control LP,the addition of histidine(His),isoleucine(Ile),lysine(Lys),threonine(Thr)and tryptophan(Trp)in the LP diet significantly increased the rats weight gain(P <0.01),but still significantly lower than the positive control.Compared with the negative control group,the feed intake of the LP diet supplemented by Lys and His rats was significantly increased(P<0.05).The visceral weight of the test group was significantly reduced compared with the positive control group(P<0.05),but there was no significant difference compared with the negative control.Compared with the negative control group,the body weight of the Lys group increased significantly,and the weight of the Thr group and limbs increased significantly.Except for the arginine(Arg)and phenylalanine(Phe)groups,the plasma amino acid concentration of the other experimental groups changed with the type of amino acids added.The plasma amino acid concentration of the Arg and Phe groups was not affected by the test treatment.The most affected non-essential amino acids(NEAA)in the experimental group were alanine,glutamine,glycine,serine,and cysteine(P<0.05),which indicates that the addition of a single essential amino acid can cause amino acid imbalance and may cause amino acid imbalance.Increase liver amino acid metabolism.Compared with the negative control group,the phosphorylation level of mTOR and its downstream signaling protein P70S6K1 was significantly increased in the low protein added Lys and Thr group(P<0.05),and there was also a significant difference compared with the positive control group(P<0.05).Compared with the positive control group,the level of phosphorylation of 4EBP1 protein was significantly reduced in the low-protein-added His,Lys,and Thr groups(P<0.05),but there was no significant difference between the experimental groups.Compared with the negative control group,low protein-added His showed no significant difference in phosphorylation between mTOR and P70S6 K.The results show that the addition of Lys and Thr can promote the phosphorylation of skeletal muscle mTOR signaling pathway,which may stimulate skeletal muscle protein synthesis and promote growth and development through mTOR.In conclusion:1.Reducing the crude protein content in feed can reduce the level of protein anabolic metabolism in rats,and improve the nitrogen utilization efficiency in feed.2.Compared with diets with a protein level of 6%,the addition of His,Lys,Ile,Trp and Thrcan increase body weight and increase nitrogen utilization efficiency in growing rats.3.Lys and Thr may stimulate skeletal muscle protein synthesis through the mTOR pathway and play a positive role in regulating growth.