The in vivo localization of the glucocorticoid receptor(GR) was studied in
cartilage and bone cells of femurs of young adult rats. Deparaffinized sect
ions were treated with a polyclonal antibody raised against the amino-termi
nus of human GR; the immunoreaction was detected with the streptavidin-biot
in amplification method. Histomorphometric, computer-assisted analysis of G
R-positive cells was performed by counting the percentage of GR-immunostain
ed cells in the proliferative and maturative/hyperaophic zone of the epiphy
seal growth plate cartilage, and of the percentage of positive osteoblasts
(OBs), osteoclasts (OCLS) and osteocytes (OCs) in the metaphyseal secondary
ossification zone. Numbers of OBs and OCLs per mm of metaphyseal endosteal
perimeter, and numbers of OCs per mm(2) of trabecular area were also count
ed. Immunopositive cells were found both in cartilage and bone, with variab
le degree of nuclear and/or cytoplasmic immunostaining; immunonegative cell
s were present among the positive ones. Histomorphometry showed that about
54% of chondrocytes in the proliferative zone, and 55% of chondrocytes in t
he maturative/hypertrophic zone of the growth plate were labeled; in metaph
yseal bone, 68% of OBs, 65% of OCs, and 98% of OCLs were GR-positive. The d
ensity of positive cells was 12.06 OBs/mm, 3.32 OCLs/mm, and 520.40 OCs/mm(
2). These results, for the first time obtained in vivo, show that GR is pre
sent in cartilage and bone cells, and that the degree of GR-immunostaining
is variable in the same type of cell. This may be dependent on the cell cyc
le and stage of differentiation, and may reflect a variable cellular sensit
ivity to the stimulation of the glucocorticoid hormone.