Postnatal variations in the number and size of C-cells in the rat thyroid gland.

The heterogeneous distribution of thyroid C-cells has until now hindered an objective evaluation of changes caused by age or experimental stimuli. To overcome this, a rigorous methodology has been designed to detect variations in shape, size, and number of C-cells throughout development. Using this methodology, we have demonstrated that C-cells do not significantly alter their shape with age. However, their volume increases gradually from 472 microns3 in newborn rats to 1653 microns3 in 120-day-old animals. Over the same time period, the mean number of C-cells within the thyroid gland increased 9-fold (from 1.6 x 10(4) to 1.5 x 10(5), and the number of C-cells per unit area decreased (from 6.15 x 10(4)/mm3 to 2.6 x 10(4)/mm3). We conclude that there are marked variations in size, total number, and number of C-cells per unit area in the rat thyroid gland after birth.