CALCITONIN AND CALCITONIN-GENE-RELATED PEPTIDE MESSENGER-RNA DETECTION IN A POPULATION OF HYPERPLASTIC PARATHYROID CELLS ALSO EXPRESSING CHROMOGRANIN-B

BACKGROUND: In contrast to chromogranin A, chromogranin B is found onl y in small amounts in parathyroid tissue. We have recently shown that hyperplastic parathyroid glands occasionally show a pronounced focal c hromogranin B expression. The aim of the present study was to further investigate the properties of these chromogranin E-positive cells by m eans of immunohistochemistry and in situ hybridization. EXPERIMENTAL D ESIGN: Routinely processed tissues hom 22 normal, 86 hyperplastic, and 36 neoplastic parathyroid glands were immunohistochemically investiga ted with Ab against parathyroid hormone (PTH), chromogranin A and E, c alcitonin, and calcitonin gene-related peptide (CGRP). Additionally, s ix hyperplastic glands with focal chromogranin immunoreactivity as wel l as chromogranin B-negative normal, hyperplastic, and neoplastic (two cases each) glands were used for in situ hybridization studies for th e demonstration of calcitonin and CGRP mRNA. RESULTS: Ah normal, hyper plastic, and neoplastic parathyroids were immunohistochemically PTH- a nd chromogranin A-positive. Twelve of 86 hyperplastic glands showed a focal chromogranin B immunoreactivity; in 10 out of these 12 cases, ca lcitonin could be colocalized with chromogranin B, chromogranin A, and PTH. CGRP was found in a fraction of calcitonin-positive cells in fou r cases. In hyperplastic glands, calcitonin mRNA was detected in areas with immunohistochemical calcitonin and chromogranin B positivity. CG RP mRNA was demonstrated only in a few cells. CONCLUSIONS: The results from this study demonstrate that calcitonin and CGRP may be synthesiz ed and stored in PTH-producing hyperplastic parathyroid cells. The cal citonin-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.