Changes in the circulating IGF system during short-term fasting and refeeding in rats.
There is little information on free insulin-like growth factor I (IGF-I) and its regulatory proteins during fasting and refeeding. Therefore, we examined rats during fasting (0, 1, 2, and 3 days) and refeeding (3, 6, and 12 h and 1, 2, 3, and 7 days) (n = 6-9). Serum was analyzed for insulin, C-peptide, growth hormone (GH), free and total IGF-I, IGF-binding protein (IGFBP)-1 and -3, and the acid-labile subunit (ALS). Additionally, liver mRNA for IGF-I, IGFBP-1, and ALS was determined. Fasting reduced serum levels of GH, free and total IGF-I, IGFBP-3, and ALS, whereas IGFBP-1 was increased (P < 0.0001). Refeeding normalized IGFBP-1 at 3 h and GH at 12 h. Free IGF-I changed in parallel with total IGF-I, ALS, and IGFBP-3, being normalized at 48 h of refeeding. IGFBP-1 (peptide and mRNA) correlated inversely with insulin and C-peptide (P < 0.001). The correlation between peptide and mRNA was relatively strong for IGFBP-1 (r(2) = 0.36; P < 0.0001), moderate for IGF-I (r(2) = 0.18; P < 0.0005), and insignificant for ALS. In conclusion, insulin appears to regulate IGFBP-1 in fasted and refed rats. However, the normal inverse relationship between free IGF-I and IGFBP-1 was absent, and free IGF-I changed in parallel with total IGF-I and thus ALS and IGFBP-3. Finally, the regulation of the hepatic synthesis of IGF-I, IGFBP-1, and ALS seems to differ substantially.
Frystyk
J
J
Kolling Institute of Medical Research, Royal North Shore Hospital, University of Sydney, Sydney, New South Wales 2065, Australia. jan@frystyk.dk
Delhanty
P J
PJ
Skjaerbaek
C
C
Baxter
R C
RC
D000821:Animal Feed; D000818:Animals; D002096:C-Peptide / Q000097:blood; D002352:Carrier Proteins / Q000097:blood / Q000235:genetics; D005215:Fasting / Q000502:physiology*; D006023:Glycoproteins / Q000097:blood / Q000235:genetics; D019382:Human Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood / Q000235:genetics; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013002:Somatomedins / Q000378:metabolism*; D013997:Time Factors
D002096:C-Peptide; D002352:Carrier Proteins; D006023:Glycoproteins; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018972:Insulin-Like Growth Factor Binding Protein 3; D012333:RNA, Messenger; D013002:Somatomedins; C075944:insulin-like growth factor binding protein, acid labile subunit; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I