Regulation of insulin-like growth factor-II production in bone cultures.
Although bone matrix is a rich source of insulin-like growth factor-II (IGF-II), little is known about the regulation of its synthesis by bone cells. This is due in part to the lack of simple and reliable assays to measure IGF-II. We have developed a method to dissociate IGF-II from its binding proteins by acidification and ultrafiltration, and quantitated IGF-II by RIA in 24- to 72-h cultures of 21-day-old fetal rat calvariae. The coefficient of variation of the assay was 13.8% or less; the recovery of IGF-II was 30-50%, and IGF-I cross-reacted 1% or less in the assay compared to IGF-II standards. The IGF-II concentrations in calvarial culture medium were in the 1- to 3-nM range, and these levels were suppressed by cycloheximide (3.6 microM) by almost 80%. Continuous treatment with placental lactogen, PTH, GH, insulin, or T3 did not modify IGF-II concentrations in 24- to 72-h cultures. Treatment with 17 beta-estradiol, testosterone, and 1,25-dihydroxyvitamin D3 also had no effect on IGF-II levels, whereas cortisol (10-100 nM) decreased IGF-II concentrations by 20-50%. Transforming growth factor-beta, prostaglandin E2, and platelet-derived growth factor BB did not alter IGF-II levels, and basic fibroblast growth factor (0.06-6 nM) for 72 h decreased calvarial IGF-II by 30-50%. In conclusion, 21-day-old fetal rat calvariae secrete IGF-II, and its concentration in culture medium is decreased by cortisol and basic fibroblast growth factor.
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105.
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Canalis
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Centrella
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McCarthy
D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D046508:Culture Techniques; D006728:Hormones / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis*; D009994:Osmolar Concentration; D011863:Radioimmunoassay; D012886:Skull
D006728:Hormones; D007335:Insulin-Like Growth Factor II