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. 2017 Sep;24(6):1117-1125.
doi: 10.1016/j.sjbs.2015.05.006. Epub 2015 May 13.

Histological and ultrastructural alterations of rat thyroid gland after short-term treatment with high doses of thyroid hormones

Njia M Ali Rajab  1 , Mirela Ukropina  1 , Maja Cakic-Milosevic  1
Affiliations

Histological and ultrastructural alterations of rat thyroid gland after short-term treatment with high doses of thyroid hormones

Njia M Ali Rajab et al. Saudi J Biol Sci. 2017 Sep.

Abstract

The aim of the present study was to investigate histological alterations of rat thyroid gland after short-term treatment with supraphysiological doses of thyroid hormones. Rats from experimental groups were treated with triiodothyronine (T3) or thyroxine (T4) during five days. In both treated groups, thyrocyte height was reduced and follicular lumens were distended. Progressive involutive changes of the thyroid parenchyma were apparent, including follicular remodeling (fusion) and death of thyrocytes. Morphological changes confirmed by quantitative analysis were more pronounced in the T4-treated group. Our results demonstrate that thyrotoxicosis, whether induced by T3 or T4, leads to different grades of thyroid tissue injury, including some irreversible damages. These changes might be explained at least in part by lack of trophic and cytoprotective effects of the thyroid stimulating hormone. Since the period required for morphophysiological recovery may be unpredictable, findings presented here should be taken into consideration in cases where the thyroid hormones are used as a treatment for thyroid and non-thyroid related conditions.

Keywords: Electron microscopy; Light microscopy; PI, propidium iodide; T3, triiodothyronine; T4, thyroxine; TRH, TSH-releasing hormone; TSH, thyroid stimulating hormone; Thyroid gland; Thyroid hormones; Wistar rats.

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Figures

Figure 1
Figure 1
Thyroid follicles from control (a and d), T3- (b and e) and T4-treated rats (c and f), paraffin (a–c, hematoxyline/eosin) and plastic (d–f, toluidine-blue) embedded sections. Note thinning of the interfollicular barrier (arrowheads in c, e and f) and desquamated thyrocytes within the follicular lumen (asterisk in c). Bar 10 μm (a–c) and 4 μm (d–f).
Figure 2
Figure 2
Percentage of PI-positive nuclei in thyroids of control and TH treated animals. Percentages of PI-positive nuclei in thyroids of T3-treated rats (7.1 ± 0.12, *p < 0.05) and T4-treated rats (9.1 ± 0.44, **p < 0.01) were significantly higher than in control animals (3.7 ± 0.53).
Figure 3
Figure 3
PI-labeled nuclei (arrows) in the follicular lumen of control rats (a) and within follicular wall of T3- and T4-treated rats (b and c). Bar 40 μm (a–c).
Figure 4
Figure 4
Follicular epithelium of control, T3- and T4-treated rats (a, b and c); t – thyrocyte, n – nucleus, m – mitochondrion, l – lysosome, g – Golgi complex, er – endoplasmic reticulum, co – colloid, e – erythrocyte in the capillary lumen. Insets show apical pole of thyrocytes, with reduced and disorganized microvilli in T3- and T4-treated rats. Bar 4 μm (a–c) and 1.5 μm (insets).
Figure 5
Figure 5
Gradual injury of thyrocytes leading to dissolution of the interfollicular barrier. Note nuclear changes (n on a–e), intracytoplasmic vesiculation (asterisk on c) and cellular debris (db) in the follicular lumen (d and e); arrowheads show thinning and dissolution of interfollicular barrier. Bar 2 μm (a–e) and 5 μm (f).
Figure 6
Figure 6
Thyrocytes from animals treated with thyroid hormones, with deformed nuclei and vesiculated endoplasmic reticulum; inset shows cell debris in the follicular lumen (a); erythrocytes in the colloid observed after treatments with T3 or T4 (b); n – nucleus, co – colloid, e – erythrocyte. Bar 2 μm (a) and 5 μm (b).
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