| Reducing dietary protein level is one of the important ways to improve the utilization efficiency of nitrogen nutrients and reduce nitrogen emissions.The purpose of this experiment was to investigate the effects of different protein diets level on the substance metabolism,intestinal mucosal flora and intestinal immune function in SD rats.Ninety healthy SD male rats weighing 180 g to 200 g were selected and randomly divided into three groups with six replicates in each group and five rats in each replicate.Three groups were fed the following diets:10.0%CP diet group,14.0%CP diet group,20.0%CP diet group(control group).The experimental period was 42 days,during which body weight and food intake of rats were recorded.After the end of the experimental period,serum and whole blood of rats were collected for the determination of biochemical indexes,lymphocyte subsets and blood routine.After the execution,the tissues were collected,and the liver,colon mucosa and colon chime were collected for the determination of substance metabolism,intestinal mucosal immune indicators,intestinal microbial flora and metabolize.The results showed that:(1)compared with 20.0%CP group,the average daily weight gain of10.0%CP group and 14.0%CP group decreased significantly(P<0.01).The serum glucose concentration of the two low-protein treatment groups was significantly higher than that of the20.0%CP group(P<0.05),and the serum urea level significantly decreased with the decrease of dietary protein level(P<0.05).The serum triglyceride concentration of the 14.0%CP group was significantly higher than that of the 10.0%CP group and the 20.0%CP group(P<0.05).When the dietary protein level was reduced to 10.0%,the serum total cholesterol concentration and HDL concentration significantly increased(P<0.05).Compared with the 20.0%CP group,the serum glucagon-like peptide-1 and fasting insulin concentrations of the rats in the 10.0%CP group and the 14.0%CP group were significantly reduced(P<0.01),and the lepton levels in the 10.0%CP group were significantly lower(P<0.01),and the glycogen concentration in the 14.0%CP group was significantly higher(P<0.05).Based on the analysis of the colonic mucosa metabolomics by LC-MS,the results showed that compared with 20.0%CP group,the relative concentrations of metabolites such as L-Lysine,L-Valise,O-Acetyl-L-serine and glycerol in the 14.0%CP group decreased significantly(P<0.05),and the relative concentrations of metabolites such as adenylic acid,Citrate acid,and L-serine hydrochloride were significantly increased(P<0.05).Metabolite enrichment analysis showed that the metabolic pathways mainly affected the regulation pathway of adipocyte lipolysis,cysteine,methionine metabolism pathway,ABC transporter protein and carbon metabolism pathway.When the dietary protein level decreased to 10.0%,it mainly affects lipid metabolism-related pathways,amino acid biosynthesis and metabolic pathways,and theIIIrelative concentrations of metabolites such as DL-2-Aminoadipic acid,L-threonine,betaine aldehyde and glycerol increased significantly(P<0.05).Compared with 20.0%CP group,the protein expression levels of liver AMPK and SREBP-1 in both 10%CP group and 14.0%CP group were significantly reduced(P<0.05),and the protein expression levels of liver AMPK in 10%CP group were lower than those in 14.0%CP group(P<0.05).(2)The results of Alpha diversity analysis showed that the colonic microbial diversity of rats in the 14.0%CP group was significantly higher than that in the 20.0%CP group(P<0.05).At the level of phylum,the predominant microflora of colonic microflora in each treatment group were Fiemicutes,Bacteriodetes,Proteobacteria and Verrucomicrobia microflora,while at the level of genus,the dominant flora were Lachnospiraceae,Lactobacillus and Romboutsia.Further differential flora screening results showed Streptococcus was the dominant flora in the 20.0%CP group.When the dietary protein level decreased from 20.0%to 14.0%,Lachnospiraceae is the dominant genus of colonic microorganisms.When the dietary protein level decreased to 10.0%,Clostridiale and Turicibacter were the dominant bacteria,and their relative abundance has increased.(3)Compared with the 20.0%CP group,the percentage of CD3~+CD8~+in blood lymphocyte subsets of rats in the 10.0%CP group was significantly increased(P<0.05).When the dietary protein level was reduced to 10.0%and 14.0%,the blood leukocyte and lymphocyte counts were significantly higher than those in the 20.0%CP group(P<0.05),and the percentage of eosinophils was significantly reduced(P<0.05).The percentage of neutrophils in the 14.0%CP group was significantly higher than that in the 20.0%CP group(P<0.05),while the percentage of lymphocytes was significantly lower than that in the 10%CP group and 20%CP group(P<0.05).The height and crypt depth of villus in the colon of rats in the 10.0%CP group were significantly higher than those in the 14%CP group and 20%CP group(P<0.05),but the ratio of villus height to crypt depth was not significantly different among the groups(P>0.05).Compared with the 20.0%CP group,the serum D-lactic acid content of the rats in the 10.0%CP group and the 14.0%CP group was significantly reduced(P<0.05),and the content of diamine oxidase was significantly increased(P<0.05).When the dietary protein level was reduced to 10%,the number of colonic epithelial lymphocytes increased significantly(P<0.05).Compared with the 20.0%CP group,the expression of NOD2 and NF-κB proteins was significantly increased in the colon mucosa of the 10.0%CP group.(P<0.05),the protein expression of NF-κB in the colonic mucosa of the 10.0%CP group was significantly higher than that of the 14.0%CP group(P<0.05).In summary,when the dietary protein level decreased from 20.0%to 10.0%and 14.0%,It caused a series of changes in rats,including decreased growth performance;The lipid metabolism of the body was abnormal,abnormal lipid metabolism and amino acid metabolism in the colonic mucosa,energy metabolism enhancement,hepatic AMPK signaling pathway was activated,and adipocyte decomposition was enhanced.The microbial population related to amino acid fermentation in the colon contents was reduced,the microbial population related to carbohydrate decomposition was increased.The number of serum immune cells in rats increased,the permeability of colonic mucosa decreased,content of epithelial lymphocytes and immunoglobulin increased,and the and the NF-κB immune response was activated.Among them,the change was most obvious in 10.0%CP group. |
