Calcitonin and calcitonin gene-related peptide mRNA detection in a population of hyperplastic parathyroid cells also expressing chromogranin B.

BACKGROUND: In contrast to chromogranin A, chromogranin B is found only in small amounts in parathyroid tissue. We have recently shown that hyperplastic parathyroid glands occasionally show a pronounced focal chromogranin B expression. The aim of the present study was to further investigate the properties of these chromogranin B-positive cells by means of immunohistochemistry and in situ hybridization.

EXPERIMENTAL DESIGN: Routinely processed tissues from 22 normal, 86 hyperplastic, and 36 neoplastic parathyroid glands were immunohistochemically investigated with Ab against parathyroid hormone (PTH), chromogranin A and B, calcitonin, and calcitonin gene-related peptide (CGRP). Additionally, six hyperplastic glands with focal chromogranin immunoreactivity as well as chromogranin B-negative normal, hyperplastic, and neoplastic (two cases each) glands were used for in situ hybridization studies for the demonstration of calcitonin and CGRP mRNA.

RESULTS: All normal, hyperplastic, and neoplastic parathyroids were immunohistochemically PTH- and chromogranin A-positive. Twelve of 86 hyperplastic glands showed a focal chromogranin B immunoreactivity; in 10 out of these 12 cases, calcitonin could be colocalized with chromogranin B, chromogranin A, and PTH. CGRP was found in a fraction of calcitonin-positive cells in four cases. In hyperplastic glands, calcitonin mRNA was detected in areas with immunohistochemical calcitonin and chromogranin B positivity. CGRP mRNA was demonstrated only in a few cells.

CONCLUSIONS: The results from this study demonstrate that calcitonin and CGRP may be synthesized and stored in PTH-producing hyperplastic parathyroid cells. The calcitonin-positive cells also strongly express chromogranin B, which is immunohistochemically not detectable in normal parathyroid cells. The functional significance of these findings remains to be elucidated.