The effects of altered nutritional status upon insulin-like growth factors and their binding proteins in neonatal rats.
To investigate the role of nutrition in the regulation of IGFs during the perinatal period, 10-d-old rats were infused intravenously with various concentrations of nutrients for 24 h. Breast-fed litter mates served as controls. The effect of caloric intake on concentrations of IGF-I and IGF-II as well as IGF-binding proteins in serum, liver, and brain of neonatal rats was studied. A total of 45 rats from 10 litters was infused with solutions ranging from a caloric intake of 0 (saline) to 75% (glucose, amino acids, and lipids) of the estimated intake of control rats. In serum, both IGF-I and -II concentrations fell markedly in response to fasting. Serum IGF-II levels were linearly related to caloric intake in the pooled data from all groups. Concentrations of IGF-II, but not IGF-I, in liver and brain were depressed by caloric restriction. In contrast to the fall in IGF concentrations, activity of IGF-associated binding proteins rose in serum and in liver cytosol 2- to 4-fold in response to decreased nutrient intake. In serum, but not liver, the rise in binding protein activity was inversely related to to caloric intake. In liver, cytosol, but not serum, the rise in binding protein activity was inversely related to total serum amino acid concentration. Thus, IGF concentrations in preweanling rats change in response to alterations of nutrient intake. The fasting induced decrements in IGF levels, as well as the elevations in IGF-associated binding protein activity, may serve as a protective mechanism to depress growth in times of caloric restriction.
Philipps
A
A
Department of Pediatrics, University of Connecticut Health Center, Farmington 06032.
Drakenberg
K
K
Persson
B
B
Sjögren
B
B
Eklöf
A C
AC
Hall
K
K
Sara
V
V
D000818:Animals; D000831:Animals, Newborn / Q000097:blood*; D002352:Carrier Proteins / Q000097:blood*; D002149:Energy Intake; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000097:blood*; D007335:Insulin-Like Growth Factor II / Q000097:blood*; D008297:Male; D009752:Nutritional Status; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000097:blood*
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II