Moderate caloric restriction increases type 1 IGF receptors and protein synthesis in aging rats.
Insulin-like growth factor-1 (IGF-1) is an anabolic hormone that mediates the actions of growth hormone (GH) and is found at lower concentrations in aged animals. These decreases in GH and IGF-1 appear to have important physiological consequences for aging, since protein synthesis decreases with age, and administration of GH and/or IGF-1 has been shown to increase protein synthesis. The present study was designed to determine (a) the relationship between the age-related changes in rates of tissue protein synthesis and plasma IGF-1 concentrations, (b) type 1 IGF receptor density in tissues and (c) whether long-term moderate caloric restriction, which is known to increase life-span, affects these relationships. Male Brown Norway rats were fed ad libitum or caloric-restricted (60% ad libitum) from 14 weeks of age and sacrificed at different ages. In ad libitum fed animals there were age-related decreases in plasma IGF-1 concentrations (14%) and in the rates of protein synthesis of the heart (36%) and liver (38%). Type 1 IGF receptor density remained constant in all tissues with age. The caloric-restricted animals exhibited plasma IGF-1 concentrations 33 to 42% lower than the ad libitum fed animals. However, rates of protein synthesis increased by 70 and 30% in heart and diaphragm, and this increase was associated with 60 to 100% increases in type 1 IGF receptor densities when compared with ad libitum fed animals.(ABSTRACT TRUNCATED AT 250 WORDS)
D'Costa
A P
AP
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-1083.
Lenham
J E
JE
Ingram
R L
RL
Sonntag
W E
WE
D000375:Aging / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000097:blood* / Q000235:genetics; D002149:Energy Intake / Q000502:physiology*; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D008099:Liver / Q000378:metabolism; D008297:Male; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011914:Rats, Inbred BN; D013002:Somatomedins / Q000235:genetics / Q000378:metabolism*
D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I