Immunohistochemical Demonstration of Parathyroid Hormone Binding to Specific Cell Types in Fixed Rat Bone Tissue

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Abstract
Deparaffinized sections of fixed decalcified neonatal rat radii were incubated in bovine PTH [parathyroid hormone] (bPTH; 1-10 MRC units/ml) or in PTH-solvent. They were then stained for PTH by the peroxidase-antiperoxidase method using guinea pig antiserum to bPTH and the substrate 3,3''-diaminobenzidine-H2O2. Staining caused by nonspecific binding of PTH to the bone matrix and the glass slides supporting the sections in 100% normal goat serum. Cross-reactivity of the antiserum to erythrocytes was eliminated by preabsorption of the antiserum with fixed rat erythrocytes. After the cross-reactivity of the anti-PTH antiserum to erythrocyte components and the nonspecific binding of PTH to bone matrix were eliminated, intense staining over the cytoplasm of the osteoclasts was demonstrated in rat radii sections incubated with PTH. Less intense staining was observed over the osteocytes, periosteal osteoblasts, and, possibly, the endosteal osteoblasts. An explanation for this differential staining could be that osteoclasts have a greater receptor number and/or a greater receptor affinity for the bPTH than do osteocytes and osteoblasts. Binding of PTH to bone tissue can be localized in all identifiable osteoclasts, osteocytes and osteoblasts, and suggests that all 3 cell types can interact directly with PTH.