Increased serum clearance and degradation of 125I-labeled IGF-I in protein-restricted rats.
Dietary protein restriction in young rats stunts growth and decreases serum insulin-like growth factor I (IGF-I) concentrations. To investigate the possibility of a diet-induced accelerated clearance of IGF-I, the clearance of 125I-labeled IGF-I was determined by measuring the radioactivity in serum obtained at different intervals after bolus injection in 5-wk-old rats that had received either a normal 15% protein diet (P15; n = 6) or a 5% protein isocaloric diet (P5; n = 7) for 1 wk. The clearance and volume of distribution of 125I-IGF-I were increased in P5 rats by 58 and 75%, respectively, whereas the terminal elimination half-life was not changed. The calculated IGF-I production rate was decreased by 40% in P5 rats. The intermediate distribution phase (alpha) was twofold faster in P5 than in P15 animals, and 125I-IGF-I was preferentially bound to IGF binding proteins in the 40-kDa complex in P5 rats. These observations might explain the increased clearance and degradation of IGF-I in the P5 rats. Dietary protein restriction appears to lower serum IGF-I concentrations by both decreasing its production rate and increasing its clearance.
Thissen
J P
JP
Department of Pediatrics, School of Medicine, University of North Carolina, Chapel Hill 27599.
Davenport
M L
ML
Pucilowska
J B
JB
Miles
M V
MV
Underwood
L E
LE
D000818:Animals; D004044:Dietary Proteins; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D007457:Iodine Radioisotopes; D011488:Protein Deficiency / Q000097:blood* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution
D004044:Dietary Proteins; D007457:Iodine Radioisotopes; D007334:Insulin-Like Growth Factor I