Light and electron microscopic study of the thyroid gland of female albino rats after collagen-induced arthritis

ABSTRACT

Adult female albino rats were subjected to experimental arthritis by the injection of arthritic material formed of bovine collagen II dissolved in acetic acid and mixed with Incomplete Freund's Adjuvant [IFA]. Thyroid glands were processed for light and electron microscopic examination. Two groups of control rats were used. The first control group comprised healthy non-treated rats. The second control group comprised IFA -treated rats. Compared with the control rats, light microscopic examination of the thyroid gland of the arthritic rats revealed a marked distortion of the thyroid architecture. The thyroid follicles appeared either degenerated, homogenized or lost. The follicular cells appeared low cubical or flattened with scanty cytoplasm and darkly stained nuclei. The parafollicular C-cells were ill-defined. The colloidal material was either highly vacuolated or depleted. Intraluminal and interfollicular mononuclear cell infiltration was observed. Compared with the control rats, electron microscopic examination of the thyroid gland of the arthritic rats revealed a distorted ultrastructure of the follicular cells. The rough endoplasmic reticulum appeared dilated, distorted, vesiculated and partially degranulated. Secretory granules were rarely seen. Lysosomes and apical cytoplasmic granules were absent. Large cytoplasmic vacuoles and secretory crystalline deposits were seen in some follicular cells. The luminal border lost its apical microvilli and the follicular lumen of some cells contained crystalline colloidal deposits. The nucleus appeared folded and contained more electron-dense clumped chromatin. Pyknotic and karyolytic nuclei were observed. The C-cells showed irregular plasma membrane, disintegrated nucleus and grouping of the secretory granules at one pole of the cell. The present observations may reflect a reduction in the functional activity of the thyroid gland [hypothyroidism] in the female rats subjected to collagen-induced arthritis. Therefore, it is recommended to monitor the thyroid hormones in patients with rheumatoid arthritis and to check the presence of thyroid auto-antibodies in these patients