Rat hepatocyte insulin-like growth factor I and binding protein: effect of growth hormone in vitro and in vivo.
This study examines the regulation of insulin-like growth factor I (IGF I) and binding protein (BP) release by adult rat hepatocytes in primary culture. Increasing the density of plating of cells had a marked positive effect on the IGF I production rate per mg cell protein, with the highest rate, approximately 4 pmol/mg cell protein X 24 h, seen at densities of 1 X 10(5) cells/cm2 or higher. Cycloheximide (15 micrograms/ml) inhibited both IGF I and BP production by more than 90%, while actinomycin D (0.1 microgram/ml) caused less marked, but still significant, inhibition. Over the insulin range 30 pM-300 nM there was a 45% increase in IGF I production, but no effect on BP production. Bovine GH stimulated production of both peptides, significant effects (up to 50% stimulation) being seen at concentrations from 20-500 ng/ml. Cells from hypophysectomized rats, with serum IGF I and GH levels reduced more than 90% from normal, had IGF I and BP production rates only 7% of normal, measured after 48 h in culture. In vivo replacement with rat GH, 150 micrograms/day for 5 days by osmotic minipump, significantly restored the production of both peptides by hepatocytes. Cells isolated from rats bearing the GH-secreting tumor, MtT/W15, had IGF I and BP production rates approximately twice as high as normal. A significant stimulatory effect of bovine GH (200 ng/ml) in vitro was seen on cells from normal and hypophysectomized, GH-replaced rats, but not from unreplaced hypophysectomized, or tumor-bearing rats. The results in hypophysectomized, animals are consistent with known changes in hepatic GH receptors, while the lack of GH responsiveness in tumor-bearing rats indicates a persistence of maximal stimulation in culture. The reflection of in vivo GH status by hepatocytes cultured for 48 h suggests that messenger RNA turnover for IGF I and BP must be slow. The close parallel in the regulation of the two peptides under most conditions might be indicative of coordinated synthesis.
Scott
C D
CD
Martin
J L
JL
Baxter
R C
RC
D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005260:Female; D013006:Growth Hormone / Q000378:metabolism / Q000494:pharmacology*; D007016:Hypophysectomy; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology; D010455:Peptides / Q000378:metabolism*; D051381:Rats; D011920:Rats, Inbred WF; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D007328:Insulin; D010455:Peptides; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D003609:Dactinomycin; D013006:Growth Hormone; D003513:Cycloheximide