AJP - Endocrinology and Metabolism, Vol 267, Issue 2 E226-E233, Copyright © 1994 by American Physiological Society
Growth hormone and parathyroid hormone stimulate IGFBP-3 in rat osteoblasts
C. Schmid, I. Schlapfer, M. Peter, M. Boni-Schnetzler, J. Schwander, J. Zapf and E. R. Froesch
Department of Internal Medicine, University Hospital, Zurich, Switzerland.
Osteoblast-like cells prepared from calvaria of newborn rats produce
insulin-like growth factor (IGF) I and several insulin-like growth factor
binding proteins (IGFBPs) in vitro. Among the IGFBPs found in conditioned
cell culture medium, IGFBP-3 is the most abundant. Intact IGFBP-3, as
assessed by 125I-labeled IGF-II ligand blot analysis, is more abundant in
culture media of cells exposed to growth hormone (GH) or to parathyroid
hormone (PTH), both at 5 x 10(-9) mol/l, for 24 h. At the same time,
concentrations of IGF-I are increased in media of cells exposed to PTH but
not to GH, compared with hormone-free control cultures. IGFBP-3 mRNA is
increased in osteoblasts exposed to PTH or to GH but not in response to 5 x
10(-9) mol/l IGF-I. PTH exerts a rapid (within 2 h) stimulatory effect on
IGF-I and IGFBP-3 production, both at the message and peptide levels,
whereas GH increases only IGFBP-3, both at the message and peptide levels
(after 24 h). We conclude that IGF-I does not mediate increased IGFBP-3
production by rat osteoblasts in response to GH and PTH.
