Number and size of rat thyroid C cells: no effect of pinealectomy

A method for the estimation of the size and total number of calcitonin-containing cells (C cells) in the rat thyroid gland has been devised. The total area, the number of C cells per unit area, and the areal fraction of C cells were determined for the C cell region using step serial sections. From these data it was estimated that from 0.3 X 10(6) to 1.0 X 10(6) C cells were evenly divided between the two thyroid lobes. Approximately 150 micron3 of cytoplasm were associated with each of these cells. In comparison with sham-operated rats, pinealectomy had little effect on the number of C cells. In an experiment terminated in the summer, there was a statistically insignificant decrease 6 weeks postsurgery; no effect was seen at 12 weeks. On the other hand, a slight increase in the number of C cells was seen in January, 12 weeks postsurgery. The volume of cytoplasm per cell was not altered by pinealectomy.