Effects of glucocorticoids on circulating levels and hepatic expression of insulin-like growth factor (IGF)-binding proteins and IGF-I in the adrenalectomized streptozotocin-diabetic rat.
Circulating levels and hepatic expression of insulin-like growth factor-binding protein-1 (IGFBP-1) are increased in insulin-deficient streptozotocin (STZ)-diabetic rats. Glucocorticoids stimulate and insulin suppresses hepatocellular expression of IGFBP-1 in vitro. We asked whether increased IGFBP-1 expression in STZ-diabetic animals is due to an effect of insulin deficiency per se or whether insulin deficiency represents a permissive state where glucocorticoids may play an important role in the regulation of IGFBP-1 and other circulating peptides involved in the modulation of IGF bioactivity. Intact female Sprague-Dawley-derived rats and rats undergoing bilateral adrenalectomy (ADNX) were injected with STZ (140 mg/kg) or buffer. Corticosterone acetate (50 mg/kg) or vehicle was administered to diabetic and nondiabetic animals immediately after ADNX and 24 h later. All rats were killed 48 h after surgery and/or STZ administration. Serum [125I]IGF-I-binding activity was increased 4-fold (P < 0.01), and Western ligand and immunoblotting demonstrated that levels of IGFBP-1 were high in intact STZ-diabetic animals. ADNX prevented these effects of STZ-diabetes, and corticosterone treatment restored serum IGF-binding activity and IGFBP-1 to intact diabetic levels. Similarly, Northern analysis demonstrated that the abundance of hepatic IGFBP-1 mRNA was increased 6-fold in intact STZ-diabetic animals (P < 0.01), but not in adrenalectomized diabetic animals. Corticosterone treatment restored hepatic IGFBP-1 mRNA to intact diabetic levels, and serum concentrations of corticosterone correlated with the abundance of IGFBP-1 mRNA (r = 0.475; P < 0.01), indicating that glucocorticoids play an important role in the regulation of expression of IGFBP-1 in insulin-deficient animals. In contrast, neither ADNX nor corticosterone altered the abundance of hepatic IGFBP-1 mRNA levels in nondiabetic animals. This pattern of regulation appeared to be specific; serum levels of immunoreactive IGFBP-2 and -4 tended to rise in adrenalectomized animals, and levels of IGFBP-3 were not affected by either ADNX or corticosterone treatment. Of note, serum levels of IGF-I by RIA were reduced in STZ-diabetic animals compared to control values (168 +/- 16 vs. 587 +/- 55 ng/ml, respectively; P < 0.01), were partially restored toward control values with ADNX (320 +/- 22 ng/ml), and were reduced again by corticosterone treatment (195 +/- 26 ng/ml), indicating that glucocorticoids also contribute to the regulation of IGF-I levels in insulin-deficient animals. The abundance of IGF-I mRNA was reduced in STZ-diabetic animals, and ADNX also partially prevented this effect of diabetes.(ABSTRACT TRUNCATED AT 400 WORDS)
Unterman
T G
TG
Department of Medicine, University of Illinois College of Medicine, Chicago.
Jentel
J J
JJ
Oehler
D T
DT
Lacson
R G
RG
Hofert
J F
JF
D000315:Adrenalectomy; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003345:Corticosterone / Q000097:blood; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000378:metabolism*; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D015151:Immunoblotting; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007659:Ketones / Q000097:blood; D008024:Ligands; D008099:Liver / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D002352:Carrier Proteins; D005938:Glucocorticoids; D018969:Insulin-Like Growth Factor Binding Proteins; D007659:Ketones; D008024:Ligands; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D003345:Corticosterone