Regulation by fasting of rat insulin-like growth factor I and its receptor. Effects on gene expression and binding.
We have examined, in liver and extrahepatic tissues, the effects of fasting on total insulin-like growth factor I (IGF-I) mRNA levels, on levels of different IGF-I mRNAs generated by alternative splicing of the primary IGF-I transcript, and on IGF-I receptor binding and mRNA levels. A 48-h fast decreased total IGF-I mRNA levels by approximately 80% in lung and liver, approximately 60% in kidney and muscle, and only approximately 30-40% in stomach, brain, and testes. In heart, IGF-I mRNA levels did not change. The levels of the different splicing variants, however, were essentially coordinately regulated within a given tissue. Specific 125I-IGF-I binding in lung, testes, stomach, kidney, and heart was increased by fasting by approximately 30-100%, whereas in brain 125I-IGF-I binding did not change in response to fasting. In tissues in which fasting increased IGF-I receptor number, receptor mRNA levels increased approximately 1.6- to 2.5-fold, whereas when IGF-I receptor number was unchanged in response to fasting, receptor mRNA levels did not change. These data demonstrate that the change in IGF-I and IGF-I receptor mRNA levels during fasting is quantitatively different in different tissues and suggest that regulation of IGF-I and IGF-I receptor gene expression by fasting is discoordinate.
Lowe
W L
WL
Diabetes Branch, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Adamo
M
M
Werner
H
H
Roberts
C T
CT
LeRoith
D
D
D000818:Animals; D005215:Fasting; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000096:biosynthesis* / Q000235:genetics; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000096:biosynthesis*
D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I