title: Age-dependent adaptation of the liver thyroid status and recovery of serum levels and hepatic insulin-like growth factor-I expression in neonatal and adult diabetic rats.
abstract: The effect of treatment with thyroxine (T(4)) on the hepatic deiodinase (5'D-I) activity and triiodothyronine (T(3)) content and on insulin-like growth factor-I (IGF-I) secretion and mRNA hepatic expression were studied in neonatal and adult diabetic (D) rats and compared with 4 thyroidectomized (Tx) groups: neonatal and adult Tx rats treated or not with T(4). Serum T(3) and T(4) decreased by 92% in both Tx populations and by 80% to 70% in D adults according to the severity of diabetes: -70 mg/kg body weight (BW) (D(70)) or 50 mg/kg BW (D(50)) of streptozotocin (STZ) injected, whereas only a 30% to 33% decrease was found in D neonates. A similar decrease of liver 5'D-I activity and T(3) concentrations was found in neonatal and adult Tx rats, whereas a significant reduction in those parameters was observed only in adult diabetics, either D(70) or D(50), but not in D neonates. Serum levels and liver mRNA expression of IGF-I determined by ribonuclease protection assay, plasma and pituitary growth hormone (GH), plasma insulin, and glycemia were also measured in both D populations. A decrease in circulating IGF-I, previously reported for Tx adult rats, was also found in both D populations. T(4) treatment recovered IGF-I and liver T(3) in both Tx groups and D neonates, but not in D adults. These results show an age-dependent adaptation of the liver thyroid economy in diabetes, as hepatic 5'D-I does not respond to diabetes in neonates and IGF-I is insensitive to T(4) treatment in adult diabetics and suggest a positive correlation between hepatic T(3) content and IGF-I expression in conditions of diabetes and Tx.
mesh_terms: D000222:Adaptation, Physiological; D000375:Aging; D000818:Animals; D000831:Animals, Newborn / Q000097:blood / Q000378:metabolism; D001786:Blood Glucose / Q000032:analysis; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D005260:Female; D013006:Growth Hormone / Q000032:analysis; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000235:genetics; D007453:Iodide Peroxidase / Q000378:metabolism; D008099:Liver / Q000737:chemistry* / Q000201:enzymology / Q000503:physiopathology*; D008297:Male; D010902:Pituitary Gland / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000503:physiopathology*; D013965:Thyroidectomy; D013974:Thyroxine / Q000008:administration & dosage / Q000097:blood; D014284:Triiodothyronine / Q000032:analysis / Q000097:blood
chemical_list: D001786:Blood Glucose; D007328:Insulin; D012333:RNA, Messenger; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D007453:Iodide Peroxidase; D013974:Thyroxine