The expression of parathyroid hormone-related protein (PTHrP) in normal parathyroid: histochemistry and in situ hybridization.

The expression and localization of parathyroid hormone-related protein (PTHrP), a major factor responsible for humoral hypercalcemia of malignancy (HHM), was investigated in 14 cases of surgically resected normal parathyroid glands. For light microscopic immunohistochemistry, formalin-fixed and paraffin-embedded specimens were stained with avidin-biotin-peroxidase complex (ABC) using the anti-PTHrP monoclonal antibody (MoAb), 4B3. Four percent paraformaldehyde (PFA)-fixed and OCT compound-embedded specimens were used for pre-embedded immunoelectron microscopy. For in situ hybridization, 4% PFA-fixed, frozen sections were studied using a bromodeoxyuridine (BrdU)-labeled PTHrP cDNA probe. Immunohistochemically, 12 of the 14 cases were positive for PTHrP, which was observed mainly in the oxyphil and transitional oxyphil cells. The chief and clear cells, on the other hand, were faintly positive. Electron microscopically, secretory granules positive for PTHrP were observed in cells containing abundant mitochondria. Consistent with the PTHrP immunoreactivity, transcripts of PTHrP were observed also in the oxyphilic cells by in situ hybridization. Thus the production and secretion of PTHrP was shown by the oxyphil cell lineage in the normal parathyroid glands.