Increased level of immunoreactive neuron-specific enolase in thyroid C cells from dogs and guinea pigs after chronic hypercalcemia.

Immunocytochemical localization of neuron-specific enolase (NSE) in thyroid C cells was investigated in various mammalian species. In bovine thyroid glands most of the C cells were weakly immunoreactive to anti-NSE antiserum. In other mammalian species, including dogs, guinea pigs, rabbits, cats, pigs, rats, hamsters, mice, and monkeys, some C cells or only a few C cells were weakly immunoreactive to the antiserum. It seems that normal C cells contain NSE in small amounts only or are devoid of NSE. After chronically induced hypercalcemia, C cells revealed hypertrophic and hyperplastic features. Whereas immunoreactive calcitonin was markedly decreased, marked increase of immunoreactive NSE was observed in C cells of both dogs and guinea pigs; almost all C cells were filled with reaction product for NSE. After administration of ethylenethiourea for a period of 3-8 months, C cells revealed a marked decrease of secretory granules and appearance of vesicular inclusions of various sizes, which were immunoreactive to the calcitonin antiserum, indicating a disturbance of calcitonin synthesis. No immunoreactivity for NSE was observed in C cells from dogs and guinea pigs so treated. In rabbits showing hypocalcemic tetany, calcitonin immunoreactivity was very intense and NSE immunoreactivity was faint to negative in the C cells. Thus, the level of NSE in C cells was clearly connected with the functional activity of the cells.