Effect of dietary proteins on the plasma immunoreactive insulin-like growth factor-1/somatomedin C concentration in the rat

Abstract

Plasma immunoreactive insulin-like growth factor-l/somatomedin C (IR-IGF-I) was determined in rats fed for 1 week on a protein-free diet, or diets containing gluten, gluten supplemented with lysine and threonine, maize-gluten meal (with arginine), maize-gluten meal (with arginine) supplemented with tryptophan and lysine, or casein. IR-IGF-1 concentration was higher in the arterial plasma of rats fed on a diet containing casein at 120 g/kg diet (4-8 U/ml) than in rats fed on a protein-free or a low-casein (SO g/kg diet) diet (15-2 U/ml). The plasma of rats fed on gluten or maize-gluten meal as the protein source showed intermediate values. However, giving a diet containing an amino acid mixture as recommended by the National Research Council (1978) but deprived of lysine or tryptophan did not affect significantly the plasma IR-IGF-1 concentration. Total IGF-1 concentration (which was measured immunologically after extraction of the plasma with acid-ethanol) was also lower in the rats fed on the protein-free diet than in those fed on the casein (120 g/kg diet) diet. The ratio IR-IGF-I: total IGF-1 was higher in the rats fed on the casein diet (120 g casein/kg diet) than in those fed on the protein-free diet. The results suggest an important influence of IR-IGF-1 or IR-IGF-1:total IGF-1 ratio on protein anabolism and nutrition. IR-IGF-1 and total IGF-1 were found in the fractions of molecular weights 40 kDa and 150 kDa after gel filtration of rat plasma. A larger amount of IGF-1 was recovered in the fraction of 150 kDa in the rats fed on the casein diet. '"I-IGF-I added to the plasma of rats fed on the protein-free diet was found mainly in the fraction of 40 kDa after gel-filtration. On the other hand, '251-IGF-1 added to the plasma of rats fed on the gluten or casein diets was mainly recovered in the free IGF-I fraction. The results suggest that 1GF-binding protein@) of molecular weight about 40 kDa was not saturated with IGF-1 in the rats fed on the protein-free diet. The results indicate the important role of IGF-1 and its binding proteins in the regulation of protein metabolism in rats.

Whole-body protein metabolism and plasma profiles of amino acids and hormones in growing barrows fed diets adequate or deficient in lysine

“…Contrary to our original hypothesis, no effect of lysine supplementation was found on GH (present study) or IGF-1 plasma concentrations (Takahashi et al 1990; present study). In many species, feed restriction results in increases of GH concentration (Buonomo and Baile 1990).…”

Nutritional and hormonal factors control the gene expression of FoxOs, the mammalian homologues of DAF-16

“…The rats were given a 12% casein diet between 1000 and 1800 h for 3 days prior to being given the experimental diet. The three diets used in the experiments of this study were a 12% casein (12C) diet, a 12% gluten (12G) diet that is deficient in lysine and threonine, and a protein-free (PF) diet, which were prepared as described previously (Takahashi et al 1990). The experiments were designed to examine the effects of protein nutritional and hormonal factors on the expression of FoxO genes.…”

Amino acid regulation of gene transcription of rat insulin-like growth factor-binding protein-1

“…IGF-I is complexed with several types of IGF-binding proteins (IGFBP) in plasma and other body fluids (Jones & Clemmons 1995), and these have been shown to play an important role in the regulation of IGF bioactivities (Jones & Clemmons 1995). Plasma concentrations of each IGFBP as well as IGF-I are affected by dietary proteins in different ways (Takahashi et al 1990, Umezawa et al 1991, Thissen et al 1994. Among the IGFBPs, the plasma concentration of IGFBP-1 was increased most strongly under protein deprivation.…”

“…From the viewpoint of body protein metabolism, IGF-I is a key factor whose plasma concentration is regulated by the quality and quantity of dietary proteins (Takahashi et al 1990). IGF-I is complexed with several types of IGF-binding proteins (IGFBP) in plasma and other body fluids (Jones & Clemmons 1995), and these have been shown to play an important role in the regulation of IGF bioactivities (Jones & Clemmons 1995).…”