Reduced ob mRNA in hypophysectomised rats is not restored by growth hormone (GH), but further suppressed by exogenously administered insulin-like growth factor (IGF) I

To examine whether GH and IGF-I participate in the regulation of obese (ob) mRNA expression we determined oh mRNA levels in epididydimal fat pads of hypophysectomised (hyper) rats, hyper rats treated with recombinant human (rh) GH or rhIGF-I and normal, weight-matched controls. We found that 1. ob mRNA was markedly suppressed after hypophysectomy (37 +/- 25% of controls), 2. GH infusion had no effect on ob mRNA, but stimulated IGF-I mRNA in fat pads, 3. IGF-I treatment further suppressed ob mRNA (3.5% +/- 0.6% of controls) and 4. serum insulin levels were decreased in all hyper groups (11.2 to 15.9% of controls). In conclusion, exogenous and GH-induced IGF-I differ in their effects on ob mRNA expression and GH is unable to restore ob mRNA towards normal at low insulin levels. (C) 1996 Academic Press, Inc.