Effect of protein restriction on plasma and tissue levels of insulin-like growth factor-1 (IGF-1) in adult rats

Abstract

The aim of the present study was to determine the influence of protein restriction on muscle, liver and plasma IGF-1 levels, and to analyze some protein and carbohydrate metabolism patterns. The experiment was carried out over period of 16 days. Male adult rats were divided into three groups: a control group (C) receiving a 12% casein diet, a group receiving a protein-free diet (A) and a protein-free diet group that was refed (AR). The following parameters were analyzed: body weight, food intake, serum IGF-1, glucose, insulin, urea and creatinine, muscle protein, and muscle and liver glycogen and IGF-1. Body weight, food intake, muscle protein, and serum and muscle IGF-1 were lower in group A than in group C, while plasma urea levels were increased. No significant difference in these parameters were observed after refeeding compared to group C. These results suggest that IGF-1 is significantly affected by the amino acid content in the diet and that the decrease in plasma and muscle IGF-1 levels is associated with relevant protein degradation, mainly in skeletal muscle. IGF-1 may therefore be considered an important indicator of nutritional status.