Effects of Decreasing Dietary Protein Level on Growth Performance, Nitrogen Balance and Skeletal Muscle Protein Turnover of Adult Rats

LIU Lu, CHU Licui, ZENG Xiangfang, QIAO Shiyan

doi:10.3969/j.issn.1006-267x.2019.05.029

2019 , Vol. 31 >Issue 5: 2222 - 2231

DOI: https://doi.org/10.3969/j.issn.1006-267x.2019.05.029

Molecular Nutrition

Effects of Decreasing Dietary Protein Level on Growth Performance, Nitrogen Balance and Skeletal Muscle Protein Turnover of Adult Rats

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State Key Laboratory of Animal Nutrition, College of Animal Science and Technology, China Agricultural University, Beijing 100193, China

Received date: 2018-11-05

Online published: 2019-05-15

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Abstract

This experiment was conducted to investigate the effects of decreasing dietary protein level on growth performance, nitrogen balance and skeletal muscle protein turnover of adult rats. Thirty-five adult SD male rats with an initial body weight of (238.6±2.3) g were selected and divided into 5 groups according to the principle of similar body weight. Each group consisted of 7 replicates, and each replicate had one rat. Rats in the 5 groups were fed 5 kinds of experimental diets which contained 20% (20%C) (this was AIN-93G standard diet), 15% (15%C), 10% (10%C), 5% (5%C) and 0 casein (0C), respectively, and supplemented with various essential amino acids according to the recommended amount of AIN-93G. The test period was 12 days, and the rats' excrement was collected on the 6th to 11th day to determine the nitrogen balance. On the 12th day morning, the rats were weighed on an empty stomach and intraperitoneally injected with L-phenylalanine (1.50 μmol/g BW containing 0.60 μmol/g BW of L-[ring-²H₅] phenylalanine). At 30 min after injection, the blood was collected from the orbital vein, and then the rats were sacrificed, the gastrocnemius and soleus muscles of the hind limbs were taken. The results showed as follows: 1) when the casein content was reduced from 20% to 15% and synthetic amino acids were added, the average daily gain of adult rats increased by 42.2% (P<0.05), but after further reducing the casein content and adding various synthetic amino acids, the growth of the rats was inhibited and the body weight decreased linearly (P<0.05). 2) The dry matter intake of rats decreased significantly when the casein content was less than 10% (P<0.05), and the nitrogen intake, total nitrogen output, nitrogen retention and nitrogen retention rate also decreased significantly (P<0.05). 3) In the gastrocnemius muscle, when the casein content of the diet decreased to 10%, 5% and 0, the muscle protein synthesis rate decreased by 18.25%, 33.65% and 40.68% (P<0.05), and the protein degradation rate increased by 17.54%, 29.82% and 35.09%, respectively (P<0.05); in the soleus muscle, the protein synthesis rate in the 15%C, 10%C, 5%C and 0C groups was significantly lower than that in the 20%C group (P<0.05), which decreased by 9.00%, 11.55%, 29.15% and 33.99%, respectively, while the protein degradation rate in the 5%C and 0C groups was significantly increased (P<0.05), which was 27.66% and 57.45% higher than that in the 20%C group. It is concluded that under the condition that all essential amino acids are supplemented step by step according to the standard requirements, when the casein content of diet for adult rats is less than 10%, the growth of rats is inhibited, body weight is decreased, nitrogen deposition and skeletal muscle protein synthesis is reduced, and skeletal muscle protein degradation is increased. Therefore, in the case of casein as the sole nitrogen source, it is appropriate to reduce the casein content of the low-protein diet for adult rats to 15%.

Key words： protein level; adult rat; growth performance; nitrogen balance; protein turnover

Cite this article

LIU Lu, CHU Licui, ZENG Xiangfang, QIAO Shiyan . Effects of Decreasing Dietary Protein Level on Growth Performance, Nitrogen Balance and Skeletal Muscle Protein Turnover of Adult Rats[J]. Chinese Journal of Animal Nutrition, 2019 , 31(5) : 2222 -2231 . DOI: 10.3969/j.issn.1006-267x.2019.05.029

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