Constitutive synthesis of insulin-like growth factor-II by primary osteoblast-enriched cultures from fetal rat calvariae.
While a number of osteotropic hormones regulate insulin-like growth factor-I (IGF-I) synthesis in osteoblast-enriched (Ob) and intact bone cultures, their direct effects on IGF-II production are still unresolved. For example, cAMP stimulators, such as PTH and prostaglandin E2, increase Ob IGF-I transcript and polypeptide levels within the first 24 h of treatment, but have no effect on IGF-II expression. To examine the possibility that other circulating factors could directly modify IGF-II synthesis by osteoblasts, primary rat Ob cultures were briefly treated with a number of polypeptide and steroid hormones known to regulate bone metabolism. Prepro-IGF-II steady state transcripts were assessed by Northern blot analysis, and immunoreactive polypeptide levels (iIGF-II) were examined by RIA. Predominant prepro-IGF-II transcripts of 3.7 kilobases were readily detected in quiescent Ob cultures, and constitutive iIGF-II levels were approximately 2-7 nM throughout the first 24 h of culture. GH, placental lactogen, insulin, cortisol, testosterone, T3, 17 beta-estradiol, and 1,25-dihydroxyvitamin D3 each had no effect on prepro-IGF-II transcripts within 6 h or on iIGF-II polypeptide expression within a 24-h period. These studies indicate that IGF-II synthesis is constitutive in unstimulated primary fetal rat Ob cultures, and that these levels are not directly modulated by short term treatment with a variety of osteotropic hormones.
McCarthy
T L
TL
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105.
Centrella
M
M
Canalis
E
E
D000818:Animals; D015152:Blotting, Northern; D002117:Calcitriol / Q000494:pharmacology; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D015342:DNA Probes; D004958:Estradiol / Q000494:pharmacology; D005333:Fetus / Q000378:metabolism*; D013006:Growth Hormone / Q000494:pharmacology; D006854:Hydrocortisone / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism*; D010928:Placental Lactogen / Q000494:pharmacology; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D012886:Skull / Q000166:cytology* / Q000196:embryology; D013739:Testosterone / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects
D015342:DNA Probes; D007328:Insulin; D011498:Protein Precursors; D013739:Testosterone; D004958:Estradiol; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone; D004247:DNA; D010928:Placental Lactogen; D002117:Calcitriol; D006854:Hydrocortisone