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 hinder ed an objective evaluation of changes caused by age or experimental st imuli. To overcome this, a rigorous methodology has been designed to d etect variations in shape, size, and number of C-cells throughout deve lopment. Using this methodology, we have demonstrated that C-cells do not significantly alter their shape with age. However, their volume in creases gradually from 472 mu m(3) in newborn rats to 1653 mu m(3) in 120-day-old animals. Over the same time period, the mean number of C-c ells within the thyroid gland increased 9-fold (from 1.6x10(4) to 1.5x 10(5)), and the number of C-cells per unit area decreased (from 6.15x1 0(4)/mm(3) to 2.6x10(4)/mm(3)). We conclude that there are marked vari ations in size, total number, and number of C-cells per unit area in t he rat thyroid gland after birth.