Regulation of insulin-like growth factor-I (IGF-I) and IGF-binding proteins by growth hormone in rat white adipose tissue.
Insulin-like growth factor-I (IGF-I) mRNA levels in rat white adipose tissue (WAT) are in the same range as those in liver, the major source of serum IGF-I, and are far above the levels in other tissues. IGF-I mRNA and IGF-I peptide levels in WAT decrease drastically after hypophysectomy and are restored to near normal by GH treatment in vivo. IGF-I gene expression in WAT from hypophysectomized rats is also stimulated by GH in vitro; half-maximal stimulation of IGF-I mRNA occurs between 0.25-0.5 nM GH, and maximal stimulation (3.5- to 5.5-fold) at 15 nM after 2 h. However, maximally stimulated IGF-I mRNA levels in vitro lie far below those measured in vivo in normal or GH-treated hypophysectomized rats. T3 does not enhance the GH effect in vitro. Rat WAT expresses the messages for IGF-binding protein (IGFBP)-2, -3, -4, -5, and -6. IGFBP-2, -3, -5, and -6 mRNAs are all regulated by GH. IGF-I mRNA and IGFBP-5 mRNA are localized in both adipocytes and stromal-vascular cells, whereas IGFBP-2 and -3 expression is restricted to stromal-vascular tissue. As physiological concentrations of IGF-I are able to induce adipocyte differentiation in vitro, we suggest that locally produced IGF-I and IGFBPs play a crucial role in the in vivo differentiation of adipose cells from stromal-vascular cells.
Peter
M A
MA
Department of Internal Medicine, University Hospital Zurich, Switzerland.
Winterhalter
K H
KH
Böni-Schnetzler
M
M
Froesch
E R
ER
Zapf
J
J
D017667:Adipocytes / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001808:Blood Vessels / Q000166:cytology / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002469:Cell Separation; D013006:Growth Hormone / Q000494:pharmacology / Q000502:physiology*; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011994:Recombinant Proteins; D013002:Somatomedins / Q000378:metabolism; D017154:Stromal Cells / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone