Focal hyperplasia of intracytoplasmic filaments in the canine parathyroid gland treated with nalidixic acid.

Focal hyperplasia of intracytoplasmic filaments of 100A in diameter was observed within chief cells of the parathyroid gland in dogs treated with nalidixic acid. The structure, as a rule, was located in the neighborhood of the nucleus and no other cell organelles were detected within it. Its size had a wide spectrum from a small part of the cytoplasm to as large as half a cell. Golgi apparatus and rough endoplasmic reticulum in the involved cells had a tendency to atrophy. These cells occasionally contained less secretory granules. Lipid droplets are diffusely increased. The pathogenesis and significance of the present intracytoplasmic filaments remain to be determined. However, as lipid deposition, atrophy of Golgi apparatus, poorly developed rough endoplasmic reticulum occur in a hypofunctional or degenerative state, it might be possible that filamentous hyperplasia is closely associated with that state.