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Departments of Research and Medicine, Saint Francis Hospital and Medical Center Hartford, Connecticut 06105
University of Connecticut School of Medicine Farmington, Connecticut 06030
Address all correspondence and requests for reprints to: Dr. Ernesto Canalis, Saint Francis Hospital and Medical Center, 114 Woodland Street, Hartford, Connecticutt 06105-1299.
Abstract
Although bone matrix is a rich source of insulinlike 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 µM) 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 17β-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- β, 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. (Endocrinology 129: 2457–2462,1991)
Footnotes
* This work was supported by Grant DK-42424 from the NIDDK and a grant from the National Osteoporosis Foundation.
Received March 6, 1991.
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