In vivo regulation of hepatic insulin-like growth factor-1 messenger ribonucleic acids with thyroid hormone.
Insulin-like growth factor-1 (IGF-1) is synthesized primarily by the liver in response to growth hormone (GH). Thyroid hormone plays a major role in mediating pituitary GH secretion. In order to clarify the effect of thyroid hormone on IGF-1 gene expression, we measured hepatic IGF-1 mRNA levels in rats with thyroid dysfunction. Female Wistar rats were rendered hypothyroid by surgical thyroidectomy or hyperthyroid by daily injections of thyroxine (12 micrograms/day) for 2 weeks. Northern gel analysis of hepatic poly (A) RNA revealed the multiple sizes of the RNA transcripts ranging from 1.6 to 9.0 kb. After 4 weeks, hepatic IGF-1 mRNA levels were suppressed in hypothyroid rats, to less than 20% of control euthyroid animals. These suppressed mRNA levels were restored to euthyroid levels by thyroid hormone replacement for 2 weeks. Hyperthyroid rats, however, did not contain altered levels of hepatic IGF-1 mRNA as compared to euthyroid rats. The gamma-actin mRNA hybridization signal was not altered in hypothyroid or hyperthyroid rats. These results suggest that thyroid hormone regulates the in vivo expression of hepatic IGF-1 mRNA, probably through the mechanism of GH regulation.
Harakawa
S
S
First Department of Internal Medicine, Nagasaki University School of Medicine, Japan.
Yamashita
S
S
Tobinaga
T
T
Matsuo
K
K
Hirayu
H
H
Izumi
M
M
Nagataki
S
S
Melmed
S
S
D000818:Animals; D015152:Blotting, Northern; D005260:Female; D015870:Gene Expression; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000097:blood / Q000494:pharmacology*; D013965:Thyroidectomy
D012333:RNA, Messenger; D013963:Thyroid Hormones; D007334:Insulin-Like Growth Factor I