Fig. 1. Paraffin and cryostat sections of euthyroid and hypothyroid rat Harderian glands (HGs). (A) The glandular cells of euthyroid rat HG contain dense basophilic secretory granules and basal nuclei. L, lumen. (B) Glandular cells from hypothyroid rat HG show pale secretory granules. The acinar lumina (L) are filled with secretory granules mixed with nuclei and cytoplasmic fragments. A and B are Mallory stained. (C) The acinar cells from euthyroid rat HG are positive for the mercury–Bromophenol Blue reaction for protein. (D) In hypothyroid rat HG some glandular cells are weakly positive for the mercury–Bromophenol Blue reaction (blue stained), whereas the others are negative (brown stained). Pycnotic nuclei (arrows) can be observed. Acini coalescing can also be observed (asterisks). (E) The glandular epithelium of euthyroid rat HG is weakly positive for the AB/PAS reaction. L, lumen. (F) Glandular cells from hypothyroid rat HG are positive for AB/PAS reaction. The lumina (L) are filled with strongly positive AB/PAS secretion. (G) Cryostat section from euthyroid rat HG. Large Sudan Black-positive vacuoles (arrowheads) and porphyrin accretions (arrows) are present in glandular cells. (H) Cryostat section of hypothyroid rat HG. A few small vacuoles stained with Sudan Black are observed outside the acini (arrows). Scale bars, 16 µm.