The feasibility of extracting and quantifying neuropeptides in bone by
radioimmunoassay was investigated in a study including 60 diaphyseal
rat femora. Substance P, calcitonin gene-related peptide, neuropeptide
Y and vasoactive intestinal polypeptide, previously identified in bon
e by immunohistochemistry, were extracted from separate homogenates of
bone, periosteum and bone marrow in a solution of 4% EDTA and 2 M ace
tic acid. Measurable amounts of all four neuropeptides in bone, perios
teum and bone marrow were obtained by radioimmunoassay in a reproducib
le manner. The neuropeptide immunoreactivities were characterized by r
everse-phase high performance liquid chromatography. Among the four ne
uropeptides analyzed, neuropeptide Y consistently exhibited the highes
t concentrations in the different tissues. Overall, cortical bone show
ed the lowest neuropeptide concentrations. The concentration of vasoac
tive intestinal polypeptide was higher in periosteum than in bone marr
ow, whereas that of calcitonin gene-related peptide was uniform in the
se tissues. The distributional differences observed in bone tissue may
be explained by a variety of physiological roles attributed to neurop
eptides such as regulation of nociception, vasoactivity, immune functi
on and local bone metabolism. The described methodology offers a new m
eans of investigating a neuropeptidergic involvement in various disord
ers of the skeleton.