Nutritionally-induced changes in hepatic insulin-like growth factor I (IGF-I) gene expression in rats.

We have used [32P]-labeled human and mouse IGF-I cDNA probes to identify three hepatic IGF-I transcripts (8.0, 1.8 and 1.1 kilobase) in rats and to quantify nutritionally-induced changes. During fasting, the major (8.0 kilobase) transcript decreased progressively after 6 h, and at 30 h was only 39% as abundant as in the nonfasted control. Refeeding animals fasted 24 h caused a marked rise in the 8.0-kb mRNA by 6 h, and an 18-fold increase at 30 h. The two minor transcripts also appeared to behave in a similar manner. Serum IGF-I concentrations paralleled levels of the major hepatic transcript during periods of both fasting and refeeding, verifying the central role of nutrition in growth regulation.