The spontaneous loss of calcitonin and somatostatin in thyroid C cells of a guinea pig.

A guinea pig showing spontaneous abnormalities in both calcitonin and somatostatin syntheses was found. Thyroid C cells revealed an almost complete absence of secretory granules immunoreactive to calcitonin and somatostatin. Instead, vesicular inclusions of various sizes, which exhibited positive immunoreactions for calcitonin and somatostatin, were found in some C cells. There were several C cells with enlarged and eosinophil cytoplasm, showing a hyaline degeneration. The number of C cells per thyroid and their distribution pattern were not different from those of normal controls. Follicular cells did not exhibit any detectable changes, whereas parathyroid glands were somewhat degenerated.