This experiment was performed to study the morphological responses of the parafollicular cells of rat following X-ray irradiation. Male rats were divided into normal and experimental groups. The head and neck region of the rat, under sodium thiopental anesthesia, was exposed to 3,000 rads or 6,000 rads of radiation in a single dose, respectively. The source was a Mitsubishi Linear Accelerator ML-4MV. The target to skin distance was 80 cm, and-the dose rate was 200 rads/min. The rate of experimental groups were sacrificed on the 6th hour, 2nd and 6th day after X-ray irradiation.
Pieces of the tissue taken from the thyroid gland were fixed in 2.5% glutaraldehyde-1.5% paraformaldehyde (0.1 M Millonig´s phosphate buffer, pH 7.3), and in 1% osmium tetroxide (0.1 M Millonig´s phosphate buffer, pH 7.3), and embedded in araldite mixture. The ultrathin sections stained with uranyl acetate and lead citrate were observed with JEM 100 CX-II electron microscope.
The results were as follow;
1. Two types of the parafollicular cells, according to their electron densities, were found, i. e., light cells and dark cells.
2. Three types of the parafollicular cells, according to their sizes of secretory granules were found, i.e., small granule cells (85 nm±20.1; 64~102 nm), medium granule cells (120 nm±26.5; 77 ~179 nm), and large granule cells (165 nm±25.7; 128~189 nm).
3. The differential ultrastructural changes of the cells according to their cell types, i.e., dark and light cell, or small, medium and large granule cells, were hardly observed in the time and dose range covered by this study.
4. The morphological changes of the parafollicular cells were not pronounced after exposure to 3,000 rads of X-ray.
5. Swollen cisternae of the granular endoplasmic reticulum and partial cytolysis were observed after exposure to 6,000 rads of X-ray.
6. Above results suggest that the parafollicular cells showed the alterations of mitochondrial and granular endoplasmic reticular swelling, and partial cytolysis, but only in doses of 6,000 rads.
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