Histopathological and biochemical changes in rat thyroid following acute exposure to hexavalent chromium.

Chromium in hexavalent form is highly toxic and a known carcinogen, although its effects on thyroid structure and function are relatively unexplored. Workers in an industrial environment can be, at times, exposed to this form of chromium. The present study was, therefore, designed using laboratory rats as a model system to investigate the effect on thyroid structure and function following two acute intraperitoneal doses of 30 mg/kg b.w. potassium dichromate administered within 48 hours. The results showed that hypothalamic chromium concentration increased (p<0.05) while thyroid chromium concentration decreased (p<0.01).The excretion of chromium in urine increased (p<0.05). The treated thyroid sections revealed hyperplasia. Follicles were disorganized, clustered and collapsed, while some of them were fused. Interfollicular spaces widened. Morphometrical analysis showed significantly (p<0.001) increased number of follicles whereas the follicular size significantly decreased (p<0.001). Nuclei were regressed (p<0.001); nuclear shapes were irregular; round, oval and shrunken. The membrane on the apical as well as the basal lamina side showed disruption. Colloid retraction within the follicles was noticeable in some sections stained with Periodic acid Schiff (PAS). Serum free tetra-iodothyronine (FT4) and free tri-iodothyronine (FT3) levels decreased (p<0.01 and p<0.001, respectively), while serum thyroid stimulating hormone (TSH) concentration increased (p<0.01). Ultrastructural analysis showed disrupted basal laminae of the follicles, regressed nuclei and disrupted cell organelles. Acridine orange stained thyroid cells demonstrated excessive dead cells, whereas DNA fragmentation assay demonstrated percent decrease of hypothalamic, pituitary and thyroidal total DNA.