Histomorphometry and quantification of nucleolar organizer regions in bovine thyroid containing methylthiouracil residues

In order to study the morphology and morphometry and to characterize and qu antify the nucleolar organizer regions (NORs) of bovine thyroids containing methylthiouracil (MTU) residues, five animals were orally treated with a s uspension of MTU (5 g/animal/day) for 20 days (group A). This treatment pro tocol was interrupted 5 days before the the animals were slaughtered. Six a nimals receiving placebos composed group B. A third group (group C) was com posed of normal thyroids obtained from a slaughterhouse. All glands were pr eviously assessed for detection of antithyroid residues by chromatography, and only those glands from MTU-treated animals were positive. Follicles of glands from group A showed wide variation in size and shape. There was a pr edominance of small follicles covered by multiple layers of columnar cells, sometimes forming papillary projections into the lumen, characterizing sev ere interfollicular and intrafollicular adenomatosis. Many follicles had va cuolated cells with nuclei showing karyolysis or pyknosis and reduced amoun ts of a low-density and very excavated colloid. They also showed higher fol licular epithelia and larger proportions of their structural components whe n compared with glands of groups B and C. In the thyroids' from group A, th e argyrophilic nucleolar organizer region-associated proteins (AgNORs) were greater in number, with small ones scattered all over the nucleus. Althoug h the size of AgNORs in thyroids from groups B and C was variable, these Ag NORs were fewer and larger than were those in glands from group A. In concl usion, the MTU induces proliferation and regressive changes in follicular c ells, and the AgNOR technique is efficient to distinguish different degrees of thyroid hyperplasia.