Cytochemical demonstration of the glucocorticoid receptor in skeletal cells of the rat

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.