Evidence for a direct effect of growth hormone on osteoblasts

In order to determine whether growth hormone (GH) exerts a direct effect on osteoblasts, in vitro and in vivo immunocytological studies were carried out on newborn rat calvaria and a clonal osteoblast-like cell line (MC3T3-E1) isolated from newborn mouse calvaria. After exposure to human growth horm...

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Bibliographic Details
Published in:Cell and tissue research 1993-08, Vol.273 (2), p.279-286
Main Authors: Morel, G, Chavassieux, P, Barenton, B, Dubois, P M, Meunier, P J, Boivin, G
Format: Article
Language:English
Subjects:
Alkaline Phosphatase - metabolism
Animals
Calcitriol - pharmacology
Cell Line
Computer Science
Growth Hormone - metabolism
Growth Hormone - pharmacology
Immunohistochemistry
In Vitro Techniques
Insulin-Like Growth Factor I - metabolism
Life Sciences
Male
Osteoblasts - drug effects
Osteoblasts - metabolism
Rats
Rats, Wistar
Receptors, Somatotropin - genetics
RNA, Messenger - genetics
RNA, Messenger - metabolism
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Summary:In order to determine whether growth hormone (GH) exerts a direct effect on osteoblasts, in vitro and in vivo immunocytological studies were carried out on newborn rat calvaria and a clonal osteoblast-like cell line (MC3T3-E1) isolated from newborn mouse calvaria. After exposure to human growth hormone (hGH) or 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), a significant increase in alkaline phosphatase activity was observed in MC3T3-E1 cells. Simultaneous exposure of MC3T3-E1 cells to hGH and 10 nM 1,25(OH)2D3 showed a synergistic effect of the two hormones on this activity. The optimal dose of hGH was 0.1 nM. An immunocytological procedure was performed on ultrathin frozen sections from 7-day-old rat calvaria and MC3T3-E1 cells cultured with hGH. GH-like immunoreactivity was observed in both cases. In calvaria, endogenous GH-like immunoreactivity was localized at the same ultrastructural level (plasma membrane, cytoplasmic and nuclear matrices) as exogenous GH-like immunoreactivity in MC3T3-E1 cells. Following the initial step of binding to the plasma membrane, GH may be internalized in the cytoplasmic matrix and nucleus. In situ hybridization revealed the presence of mRNA coding for GH receptor in calvaria cells. The density of these receptors seemed to be lower in osteoblasts than in hepatocytes. In MC3T3-E1 cells, hGH induced a dose-dependent secretion of insulin-like growth factor 1. In conclusion, these results indicate that GH may act directly on osteoblasts.
ISSN:0302-766X
1432-0878
DOI:10.1007/BF00312829