An Immunocytochemical Study on the Development and Growth of C-cells in the Rat Thyroid

Abstract

This study was performed to investigate the developmental change of the C-cells in the thyroid glands of the rats. The animal groups used in this study included 17.5-, 18.5-, 19.5-, 20.5-, 21.5-day-old rat fetuses and 3-, 7-, 15-day-old neonatal rats and adult rats weighing about 200 gm. The specimens were fixed with Souin's fluid and embedded in paraffin. Transverse serial sections of the thyroid were cut at 5 p. m from the superior to the inferior pole and eleven representative sections per thyroid lobe were selected with same intervals for immunohistochemical staining. The sections were subjected to the immunoperoxidase staining using anti-synthetic human calcitonin antibody for the detection of C-cells and counterstained with hematoxylin. Then, they were observed under the light microscope and the results were as follows: 1. Immunoreactive C-cells were first observed in the thyroid from the 20.5-day-old fetuses, but in only one and in all thyroids from 21.5-day-old fetuses. 2. The area of the thyroid gland containing C-cells, which was the posterocentral area of the lobe in 21.5-day-old fetuses, increased with aging. It occupied almost entire thyroid except for a small peripheral zone and the polar regions in the adult rats. 3. The numbers of C-cells per unit area (in this study, defined as 227 p. m X 227 fl m) of the thyroid from 21.5-day-old fetuses, 3-,7-, 15-day-old rats and adult rats were 17.8±4.8, 16.2±4.9, 20.8±4.4, 22.6±6.1, 54.7±9.3, respectively. 4. The ratios of intrafollicullar C-cells to total C-cells were 18.3%, 20.0%, 29.5%, 30.3% in the specimens from 3-, 7-, 15-day-old rats and adult rats, respectively. 5. The ratio of C-cells which appeared singly to total C-cells was decreased with aging from 88.8% in the 21.5-day-old fetus thyroids to 33.6% in the adult thyroids. 6. C-cells in the adult rat thyroids were polymorphic in shape; round, ovoid, triangular and spindle-shaped. They were relatively uniform in size with the diameter of 13.2± 2.3 p. m. C-cells in the fetal thyroid were variable in size ranging from 5.6 p.m to 11.3 p.m in diameter and had less cytoplasm than that of adult rat.