Abstract:

Objective   To investigate the effects of long-term isocaloric high-protein diet intake on insulin secretion and plasma Ghrelin in diet-induced obese rats. 〖  Methods   Diet-induced obese rat models were established by feeding with a high fat food. 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 24 weeks. Body weight and fasting blood glucose were determined during the feeding period. After 24 weeks, visceral fat mass, fasting plasma Ghrelin (by enzyme-immunoassay, EIA) and fastinginsulin (by radio-immunoassay, RIA) were assayed. To evaluate the insulin secretive function of β cells, serum levels of insulin were determined in an intravenous glucose tolerance test (IVGTT).    Results  Body weight ［(490.92±39.47)g vs (545.55±31.08)g, P＜0.01］ and visceral fat mass ［(22.42±7.04)g vs (32.33±9.27)g, P＜0.05］ in HP rats were 〖KG*3]significantly lower 〖KG*3]than those in NC rats. 〖KG*3]The serum insulin levels in 5 and 10 min 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］. HP rats had an increased trend in plasma Ghrelin level ［(2.36±0.82)ng/mL vs (1.95±0.64)ng/mL, P=0.20］. Plasma Ghrelin was negatively correlated with 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).   Conclusion  Long-term isocalorichigh-protein ingestion may reduce the first phase secretion of insulin and increase fasting plasma Ghrelin level in diet-induced obese rats. The decrease ofinsulin secretion may be secondary to Ghrelin increment and weight loss.

Key words: Models, animal; Dietinduced obesity; Protein; Insulin; Ghrelin; Rats, Wistar