Abstract
Histological investigation of the thyroid glands of rats treated with methylthiouracil, when compared with those of normal untreated. rats, elucidated the following: The treatment induces hyp e rplasia of the thyroid glands consisting of abnormally increased mitotic division and heightening of follicle cells, follicle multiplication, widespread occurrence of irregular change of follicles, loss of colloid and abnormal engorgement of capillaries. Large follicles found in the peripheral zone of the gland become very irregular in shape, the so-called “Zentralkanalchen” -like or collecting duct-like structure, and have a number of outpockets and nipple-like projections of the follicle wall. This structure does not connect further with many of the surrounding follicles through communication of the cavities. Solid and hollow b u dding processes by which new follicles are produced, are sometimes found in these irregular-sheped large follicles. New follicles are not produced by fusion or division of irregularshaped follicles or rearrangement of follicle cell broken up. Proliferative buds (Proliferationsknospe) or S an de r s o n's swellings. (S and e r so n's P o 1 s t e r), which represent a special site for for mation of new follicles, are also not produced by the treatment. Mitotic division occurs frequently, especially in irre g ular-shaped large follicles. Int r afollicular follicles are very rarely found in rats treated. Following treatment with methylthiouracil, follicle as s ociation, in which follicles are found to connect with each other without communication of their cavities in normal rats, is reduced as a result of dissociation by ingrowth of abundant interstitial tissue and increased engorgement of surrounding capillaries, but does not completely disappear. Parafollic u lar cells are impossible to find and become probably indistinguishable from follicle cells following methylthiouracil freatment. The ultimobranchial body, especially its cysts and cell cords, indicate no characteristic change leading to production of new follicles and remain unaffected by methylthiouracil treatment. No sex difference is found in the histolog i cal change of the thyroid gland by the treatment.
