Effects of sulfonamide on the pituitary-thyroid gland. 1. Morphological changes of thyroid gland and variation in plasma thyroxine and triiodothyronine.

Morphological changes of the thyroid gland on light and electron microscopy as well as concomitant variation in plasma T3 and T4 levels after oral treatment with sulfonamide at a dose of 2 g/kg for 30 consecutive days were examined in male Wistar rats. Several rats were treated with the same dose by the same route for 15 days and then put to the restoration experiment for 15 days. Plasma T3 and T4 levels significantly decreased as compared with the control in the period from the 1st day to the 30th day of the administration. A significant increase in thyroid weight was seen from the 15th day. On the 30th day, the weight was at last about eight times as heavy as that of the control. Histologically, hyperplasia of the follicles which were lined with high columnar cells was observed. The epithelial cells showed considerable pleomorphism and colloid was virtually absent at this time. As early as on the 3rd or 5th day, the follicular cells were high-columnar in shape on electron microscopy and there was an increase in rough-surface endoplasmic reticulum, the cisternae of which were dilated. Swelling of mitochondria and the absence of colloid were also noted. There were no secretory granules in the cytoplasm and numerous long microvilli projected into the lumens. On the 30th day, the follicular cells became remarkably high-columnar and had small and ovoid nuclei at their base. In the restoration study, numerous dense secretory granules and colloid droplet profiles appeared in the cytoplasm.