| BackgroundIt has been thirty years since China started reform and opening up.The dietary pattern of Chinese has undergone dramatic changes.One of the most obvious change is that the resources of high quality protein have been converted from egg and soybean to animal protein like meat&poultry or milk.Whether the dietary conversion closely relates to the development of chronic diseases need further study.Objective1.To study the effect of consuming soy and milk powder as the main sources of protein for a long time by rats on the metabolism of carbohydrate and lipid and the injury to the pancreas.2.To study the effect of consuming different sources or content of protein in different physiological stage by rats on the metabolism of carbohydrate and lipid and the injury to the pancreas.MethodsThe SPF male Wistar rats,21 days after born,were chose as our animal model.It abided by the AIN-93 standardation to prepare the animal feed.In different groups,the casein in the AIN-93 was replaced by soybean powder and meringue powder mixed production or skimmed milk powder,respectively.There were 2 kinds of protein contents in animal feeds(18%vs 9%)and 4 groups in this study.The 4 groups were LS(soybean/egg white powder,9%),HS(soybean/egg white powder,18%),LM(skimmed milk powder,9%)and HM(skim milk powder,18%),respectively.The soybean oil is the only food source of lipid in this experiment.The total energy provided by animal feeds in different groups was adjusted to be the same by changing the corn starch contents and the ratio of the energy provided in 4 groups’ animal feeds by lipid were 14%.In the groups with higher protein content,the ratio of the energy provided in the animal feeds by protein was 20%.In the groups with lower protein content,the ratio of the energy provided in the animal feeds by protein was 10%.The delactation rats were fed in the artificial feeding environment during the first week to adapt new environment.Then,they were randomly divided into 4 groups according to their weight,named as the LS group,the LM group,the HS group and the HM group.In different groups,the fats were continuously given different experimental animal feed for eight weeks as the first study stage.At the 8 th weekend,randomly executed 6 rats in each group.After that,the remainder rats in each group were randomly divided into 3 subgroups according to their weight.In the LS group,the rats in the 3 subgroups were given the same animal feeds as the LS,LM and HM group,respectively,renamed as the LS-LS group,the LS-LM group and the LS-HM group.The LM,HS and HM group were also respectively divided into 3 subgroups.Finally,there were 12 subgroups,named as LS-LS group,the LS-LM group,the LS-HM group,the HS-HS group,the HS-LM group,the HS-HM group,the LM-LM group,the LM-LS group,the LM-HS group,the HM-HM group,the HM-LS group and HM-HM group.The rats in the 12 groups were continually fed in 12 weeks as the second study stage.At the 20 th weekend,all rats were executed.The design of this experiment belongs to the nested design,the first study stage is the primary treatment factors,and the second study stage is the secondary processing factors.When the rats were planned to be executed,they were all fasted for 12 hours.Then,their serum were collected,their pancreas were totally picked up.The level of glucose,triglyceride,total cholesterol,low density lipoprotein cholesterol,high-density lipoprotein cholesterol and insulin,leptin and insulin-like growth factor-1 and adiponectin in rat serum were determined.The rat pancreas were stained by H.E.(Hematein Eosin).The microscope was used to determine the pathology changes of rat pancreas.According to the damage degree of their islets of langerhans,different score was given to each rat.Relevant statistical methods of data analysis were chosen according to the design of the experiment and the experimental data types.Results1.the results of the first study stageThe maximum of net weight gain appeared in the HS group,and the minimum of net weight gain appeared in the LM group.Both of them were significantly different from the other 3 groups.The net value of length again in HS and HM group were significantly higher than the LS and HS group.The feed efficiency in the HM group is significantly higher than the other 3 groups.In the HS and HM group,the level of GLU(glucose)in rat serum was significantly higher than the other 2 groups.In the LM group,the level of GLU is the lowest,and it was statistically significant different from the HS and the HM groups.In the HS and the HM groups,the level of TG(triglyceride)in rat serum was significantly below the LS and the LM group.The level of TC,LDL-C(low density lipoprotein cholesterol),HDL-C(high-density lipoprotein)in rat serum were no difference between each group.The level of INS(insulin)in the HS group is the highest,significantly different from the LM and the HM group.The level of LEP(leptin)in the HS group is the highest,significantly different from the LM and the HM group.The level of LEP in the HM group is the lowest,significantly different from the other 3 groups.The level of Adipo(adiponectin)in the HS group is the highest,significantly different from the LM and the HM group.There were no significantly different of the level of IGF-1(insulin-like growth factor-1)and HOMA-IR(homeostasis model assessment of insulin resistance)between each group.The pancreas of all rats did not appear obviously pathological changes.2.the results of the second study stage(1)the outcome of consuming 4 kinds of animal feeds(the group of LS-LS、HS-HS、LM-LM、HM-HM,also named as the group of LS、HS、LM and HM)There was no significantly different of the net weight gain between each group.The net weight gain in the HM group is significantly higher than the other three groups.The feed efficiency in the LS and the HS group was significantly higher than the LM and HM group.The level of GLU in rat serum in the HM group was the highest,and it was significantly different from the HS and the LS group.The level of TG in rat serum in the HS group was the lowest,and it was significantly different from the other 3 groups.The level of TC in rat serum in the HM group was the highest,and it was significantly different from the other 3 groups.The level of GLU in rat serum in the HM group was the highest,and it was significantly different from the HS and the LS group.The level of LDL-C in rat serum in the LS and the HS group was significantly lower than the LM and the HM group.The level of HDL-C in rat serum in the HM group was significantly higher than the other 3 groups.The level of INS in rat serum in the HM group was significantly higher than the HS and the LS group.The level of LEP in rat serum in the LS group was the highest,and in the LM group was the lowest.The difference was significant.The level of Adipo in rat serum in the HS group was the highest,and it was significantly different from the other 3 groups.The value of HOMA-IR in the HM group was the highest,and in the HS group was the lowest.The difference was significant.The damage of islets of langerhans in the HM group was the most serious,and it was significantly different from the LS and the LM group.The degree of the damage of islets of langerhans is positively related to the level of GLU,INS in serum,and the level of GLU is also positively related to the level of INS.In each group,the level of GLU is significantly higher in the rats with islets of langerhans damaged than those had no damaged.There was no other difference between the 2 kinds of rats.To compare with the first study stage,in the LS group,the level of TG in serum significantly dropped and the level of HDL-C in serum significantly rose.In the HS group,the level of INS and HOMA-IR in serum significantly dropped.In the LM group,the level of GLU,HDL-C and HOMA-IR in serum significantly rose.In the HM group,the level of TG,TC,HDL-C and LEPTG in serum significantly rose.The level of IGF-1 in serum significantly rose in each group.(2)the outcome of consuming 12 kinds of animal feeds(nested design experiments)Consuming the LS animal feed in the first study stage,at the end of the second study stage,the level of TC,GLU,LDL-C and HDL-C in,the LS-LM and LS-HM group was significantly higher than the LS-LS group.The level of TC:LDL-C and HDL-C in the LS-LM group was significantly higher than the LS-LM and the LS-HM group.The level of TC:HDL-C in the LS-HM group was significantly lower than the LS-LS group.The level of Adipo and HOMA-IR in the LS-LS group was significantly higher than the LS-LM and the LS-HM group.There was no dif’ference of the score,which stood for the damage degree of the islets of langerhans,among the LS-LS,the LS-LM and the LS-HM group.Consuming the HS animal feed in the first study stage,at the end of the second study stage,the level of TG,TC and LDL-C in the HS-HM group was significantly lower than the HS-LM and the HS-HM group.The level of HDL-C in the HS-HS group was significantly lower than the HS-HM group.The level of TC:LDL-C AND Adipo in the HS-HS group was significantly higher than the HS-LM group.The score,which stood for the damage degree of the islets of langerhans,in the HS-LM group was significantly lower than the HS-HM group.Consuming the LM animal feed in the first study stage,at the end of the second study stage,the level of TG in the LM-LM was significantly higher than the LM-HS group.The level of LDL-C and HDL-C in the LM-LM group was significantly higher than the LM-LS and the LM-HS group.The level of TC:LDL-C in the LM-LM group was significantly lower than the LM-LS and the LM-HS group.There was no difference of the score,which stood for the damage degree of the islets of langerhans,among the LS-LS,the LS-LM and the LS-HM group.Consuming the HM animal feed in the first study stage,at the end of the second study stage,the level of GLU and Adipo in the HM-LS was significantly lower than the HM-HS group.The level of TC in the HM-HM group was significantly higher than the HM-LS and the HM-HS group.The level of LDL-C and HDL-C in the HM-HM group was significantly higher than the HM-LS and the HM-HS group.The level of TC:LDL-C in the HM-HM group was significantly higher than the HM-LS and the HM-HS group.There was no difference of the score,which stood for the damage degree of the islets of langerhans,among the LS-LS,the LS-LM and theLS-HM group.To compare the outcome of the 12 groups,the result showed that if the first study stage were fed with animal feed containing soybean,the second study stage with milk powder,the level of GLU in rat serum would rise.If the second study stage fed with soybean,except the HM-HS group,the level of GLU in rat serum maintained lower.If the second study stage fed with milk powder,the level of GLU in rat serum maintained higher.If the first study stage were fed with animal feed containing soybean,the second study stage with milk powder,the level of TG in rat serum would rise.If the first study stage were fed with milk powder,the second study stage with soybean,the level of TG in rat serum would drop.If the second study stage fed with high level of soybean animal feed,the level of TG in rat serum maintained lower.If the second study stage fed with high level of milk powder,the level of TG in rat serum maintained higher.If the second study stage fed with soybean animal feed,the ratio of TC/LDL-C maintained higher.If the second study stage fed with milk powder,the ratio of TC/LDL-C maintained lower.If the second study stage fed with soybean,the ratio of TC/HDL-C maintained higher.If the second study stage fed with milk powder,the ratio of LDL-C/HDL-C maintained higher.The level of INS in rat serum was significantly lower in those which consumed soybean during the first study stage than consumed milk powder.The level of Adipo in rat serum was significantly higher in those which consumed soybean during the second study stage than consumed milk powder.This indicated that the changes of insulin resistance index may be the same as the changes of the level of INS in rat serum.In these 12 groups,the value of HOMA-IR in the HM-HM is the highest,and in the HS-HS group is the lowest.There were no significant differences of the level of LEP and IGF-1 in rat serum among these groups.Conclusions1.The body weight of growing rats was positively related to the dietary protein content.the greatest net gain weight of rat was in HS group,while mild powder diets have significant more effective than soybean/egg white diets at increasing body lengths of rats.2.There was no significant difference in net gain weight of rats fed by four experimental diets from delactation to adult stage.3.Compared with milk powder diets,longterm intake of soybean/egg white dits could significantly reduce the serum concentrations of TG,LDL-C,and GLU,and lower the insulin resistance risk in rats.4.The soybean/egg white diets could reduce the level of serum TG and LDL-C,increase the level of serum Adipo,and improve insulin resistance in rats fed by milk powder diets.5.Whether dietary change or not,high high protein content diets induce pancreatic pathologic damages,even result in functional damages to pancreatic islet cells in rats.The most serious injuries was HM group. |
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