title: Insulin-like growth factor-I and growth hormone have different effects on serum lipoproteins and secretion of lipoproteins from cultured rat hepatocytes.
abstract: GH has previously been shown to regulate serum lipoprotein levels and hepatic secretion of apolipoprotein-B (apo-B) and apo-E in the rat. The aim of this investigation was to study a possible role of insulin-like growth factor-I (IGF-I) in this regulation. Adult female rats were hypophysectomized and treated with recombinant human IGF-I (1.25 mg/kg.day) as a sc continuous infusion for 7 days. The effects of IGF-I were compared with those of bovine GH, given either as a continuous sc infusion or as two daily sc injections. All hypophysectomized rats were given replacement therapy with L-T4 and cortisol. Serum IGF-I concentrations increased to similar levels as a result of treatment with bovine GH and IGF-I. There was no effect of IGF-I on serum concentrations of glucose or insulin, whereas GH, independent of its mode of administration, increased serum insulin concentrations. Food intake was not affected by treatment with IGF-I. IGF-I had no effect on serum concentrations of cholesterol or apo-E, whereas GH given twice daily decreased serum cholesterol concentrations, and a continuous infusion of GH increased serum apo-E concentrations. Serum triglyceride and apo-B concentrations increased markedly as a result of IGF-I treatment, whereas GH had no effect on serum triglycerides, but decreased serum apo-B concentrations. Hepatocytes were isolated from hypophysectomized rats treated with L-T4 and cortisol alone or in combination with IGF-I and kept in short term cultures. In this system, IGF-I had no effect on the incorporation of [3H]glycerol in triglycerides or the mass of triglycerides in the cells and medium. There was no effect of IGF-I treatment on the secretion of apo-E or apo-B. Moreover, there was no effect of IGF-I treatment on the relationship between newly synthesized and secreted apo-B 48 and apo-B 100, as determined by [35S]methionine labeling of the proteins. In conclusion, the previously observed effects of GH on serum lipoproteins and hepatic apolipoprotein secretion does not seem to be mediated via IGF-I, but IGF-I has its own unique effects on serum triglyceride and apo-B levels. The increases in serum apo-B and serum triglyceride concentrations after IGF-I treatment were not dependent on increased hepatic secretion of apo-B or triglycerides.
authors.affiliation: Department of Physiology, Göteborg University, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Sjöberg
authors.forename: J
authors.initials: J
authors.lastname: Oscarsson
authors.forename: S O
authors.initials: SO
authors.lastname: Olofsson
authors.forename: S
authors.initials: S
authors.lastname: Edén
mesh_terms: D000818:Animals; D001055:Apolipoproteins B / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D001057:Apolipoproteins E / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D001786:Blood Glucose / Q000032:analysis; D001835:Body Weight / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000097:blood; D004435:Eating; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000494:pharmacology*; D008074:Lipoproteins / Q000097:blood* / Q000378:metabolism*; D008099:Liver / Q000166:cytology* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014280:Triglycerides / Q000097:blood
chemical_list: D001055:Apolipoproteins B; D001057:Apolipoproteins E; D001786:Blood Glucose; D007328:Insulin; D008074:Lipoproteins; D014280:Triglycerides; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D002784:Cholesterol