Somatostatin-like immunoreactivity in rat thyroid. Age-associated S-cell hyperplasia.

Somatostatin-like immunoreactive cells of the rat thyroid gland at various ages were investigated immunohistochemically. The number of cells per lobe in 5 micron sections increased with age. Immunopositive cells were evident as small clusters in the older age group (8 to 24 months old) but not clustered in the younger age group (3 to 5 months old). This type of proliferation was termed S-cell hyperplasia in a manner similar to C-cell hyperplasia observed in the aged rat thyroid.