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1 Department of Medicine and 2 School of Biological Sciences, University of Auckland, Auckland, New Zealand; and 3 Peptide Research Laboratories, Tulane University Medical Center, New Orleans, Louisiana 70112
Adrenomedullin is a 52-amino acid vasodilator
peptide produced in many tissues, including bone. It has 20% sequence
identity with amylin, a regulator of osteoblast growth, and circulates in picomolar concentrations. The present study assesses whether adrenomedullin also acts on osteoblasts. At concentrations of 10
12 M and greater,
adrenomedullin produced a dose-dependent increase in cell number and
[3H]thymidine
incorporation in cultures of fetal rat osteoblasts. This effect was
also seen with adrenomedullin-(15
52), -(22
52), and -(27
52), but
adrenomedullin-(40
52) was inactive. These effects were lost in the
presence of amylin blockers, suggesting they were mediated by the
amylin receptor. Adrenomedullin also increased [3H]thymidine
incorporation into cultured neonatal mouse calvaria but, unlike amylin,
did not reduce bone resorption in this model. Adrenomedullin stimulated
phenylalanine incorporation into both isolated osteoblasts and
calvaria. When injected daily for 5 days over the calvariae of adult
mice, it increased indexes of bone formation two- to threefold
(P < 0.0001) and increased
mineralized bone area by 14% (P = 0.004). It is concluded that adrenomedullin regulates osteoblast
function and that it increases bone mass in vivo. The potential of this
family of peptides in the therapy of osteoporosis should be further
evaluated.
amylin; calvaria; bone resorption; peptide fragments
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