Effects Of Long-term High-protein Diet On Ghrelin And Isletβ Cell Function In Obesity Rats

【Objective】The aim of this study is to investigate the effects of long-term isocaloric high-protein diet and regular diet intake on plasma Ghrelin, serum levels of insulin,blood glucose and body weight in diet-induced obesity rats, combine the expression of Ghrelin in stomach and insulin in pancreas,so as to probe the effect of long-term isocaloric high-protein diet intake on isletβcell,endocrine function.Meanwhile,we observed the impacts of long-term high-protein diet on kidney in obesity rats,in order to explore the relation of diets with different components and individual body.【Methods】Diet-induced obesity rat models were established by feeding Wistar rats(21days old) high calorie and high fat diet 14weeks.The obese male rats were randomly divided to two groups:the high-protein diet group(HP,36.7%of energy from protein,n=12) and the regular diet group(NC,22.4%of energy from protein,n=11).The total calorie ingestion of each rat per day was similar and was maintained for 24weeks.Body weight and fasting blood glucose(FBG) were determined during the feeding period.After 24weeks,fasting plasma Ghrelin(by enzyme-immunoassay,EIA),fasting insulin(FINS)(by radio-immunoassay, RIA),urea nitrogen(BUN),creatinine(Cr) and 24hour urine albumin(ALB) were assayed.To evaluate the insulin secretive function ofβcells,serum levels of insulin were determined in an intravenous glucose tolerance test(IVGTT).Visceral fat mass was measured after executing the rats.Ghrelin at stomach and insulin at pancreas were studied by immunohistochemical method,and the renal morphology was observed under microscope.【Results】1.Body weight and visceral fat mass:Compared with NC group,there was no significant difference in body weight of HP group(P=0.27) after 8weeks.From 16th week to 24th week,body weight in HP rats were significantly lower than those in NC rats[(490.92±39.47)g vs(545.55±31.08)g, P<0.01].The visceral fat mass[(22.42±7.04)g vs(32.33±9.27)g,P<0.05] and the percentage of visceral fat mass[(4.533±1.18)%vs(5.933±1.45)%,P< 0.05]in HP rats were both significantly lower.2.FBG,FINS and IVGTT:There were no differences in FBG levels of the HP rats and the NC rats at 12th and 24th week(P>0.05).In IVGTT,there were no differences in blood glucose levels between the two groups(P>0.05).The serum insulin levels in 5min and 10min of IVGTT were significantly lower in HP than in NC[(91.56±21.72)μIU/mL vs(121.29±34.03)μIU/mL,P<0.05;(58.62±15.80)μIU/mL vs(81.12±24.36)μIU/mL,P<0.05].The 0～30min insulin area under curve(AUC) in HP rats was significantly smaller[(175.21±41.49)μIU/mL vs(232.38±64.56)μIU/mL,P<0.05].The 0～120min insulin AUC in HP rats had an decreased tend[(227.64±54.34)μIU/mL vs(287.91±76.58)μIU/mL,P =0.086].3.Fasting plasma Ghrelin:HP rats had an increased tend in fasting plasma Ghrelin level[(2.36±0.82)ng/mL vs(1.95±0.64)ng/mL,P=0.20].Plasma Ghrelin was negatively correlated to body weight(r=-0.373,P<0.05),visceral fat mass(r=-0.454,P<0.01) and fasting insulin(r=-0.390,P<0.05).4.BUN,Cr and 24hour urine ALB:The BUN level in HP rats were significantly higher than in NC rats[(7.02±0.86)mmol/L vs(5.61±0.46)mmol/L,P= 0.001].There were no differences in Cr and 24hour urine ALB levels of the two groups(P>0.05).5.The image analysis:There were no differences in positive area of isletβcell between HP and NC rats(P>0.05).Compared with NC rats,the Ghrelin was more expressed in stomach of HP rats[(25473±8701.21) vs(10526±6194.56),P= 0.014].After HE dye,there were no differences in the kidney morphology between two groups under microscope.【Conclusion】Compared with regular diet,long-term isocaloric high-protein ingestion may reduce body weight,increase fasting plasma Ghrelin level and gastric fundus expression of Ghrelin in diet-induced obesity rats.It may reduce the first phase secretion of insulin but not change the morphology of pancreatic isletβcell.Meanwhile,there is no evidence that showed the damage of high-protein diet to kidney in our study.