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Thread: Thyroid Follicles, Various Sizes picture - Endocrine Histology Atlas

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    Default Thyroid Follicles, Various Sizes picture - Endocrine Histology Atlas

    Methods
    This quantification was performed in thyroids collected from df/df, GHRKO and df/KO female mice, at approximately 5–6 months of age. We used a computerized plotting programme that combines a live microscopic image of the slide with an operator-generated overlay.

    Results
    Inner follicular surface area and inner follicular perimeter were decreased in all examined kinds of dwarf mice as compared to normal animals. Furthermore, decreases in these two parameters were more pronounced in df/df and df/KO than in GHRKO mice. Concerning the follicular epithelium thickness, only a tendency towards decrease of this parameter was found in all three kinds of dwarf mice.

    Conclusions
    Parameters characterizing thyroid follicle size are decreased in all three examined models of dwarf mice, which may explain decreased thyroid hormone levels in both basal mutants (Ames dwarfs and GHRKOs). df/df mutation seems to predominate over GHRKO genetic intervention concerning their effects on thyroid growth. Beside TSH, also GH signaling seems to constitute a crucial element in the regulation of thyroid growth and, possibly, function.

    Keywords: Ames dwarf mice; GHRKO mice; Thyroid follicle; Inner follicular surface area; Inner follicular perimeter; Follicular epithelium thickness

    Discussion
    We have expectedly observed in our study that the inner follicular surface area and the inner follicular perimeter were decreased in all examined kinds of dwarf mice. At least two causes of such results can be considered. First, the decrease of these parameters may be a direct consequence of smaller sizes and masses of Ames dwarf (df/df), GHRKO and df/KO mice as compared to normal animals. In accordance with our observation, Bartkereported previously that the thyroid glands of Ames dwarfs and Snell mice (another kind of dwarf mice, characterized by a mutation at the transcription factor Pit-1) were greatly reduced in size, the follicles were small, and in the center of each lobe a considerable amount of the tissue was not organized into follicles. Similarly, Cordier et al demonstrated reduced follicular parameters (e.g. follicular surface and volume) in Snell mice as compared to normal mice. According to such an explanation, even lower values of measured parameters should be observed in double mutants, i.e. df/KO, as they are characterized by smaller body mass and size when compared to df/df or GHRKO mice However, both, the inner follicular surface area and the inner follicular perimeter in double mutants df/KO were the same as in case of df/df mice. This means that the additional experimental intervention, namely GHRKO, did not add anything concerning these parameters. Therefore, the lack of differences in the examined thyroid morphological parameters between df/KO and df/df mice suggests that some additional factors could exist, being responsible for such result, and presumably it may be linked to thyroid secreting function. Thus, the second cause may relate to certain factors which decrease thyroid function much stronger in df/df mice [13] than in GHRKO animals Thus, on the basis of our results we can suggest that df/df mutation predominates over GHRKO genetic intervention concerning their effects on thyroid growth and, possibly, function. However, further analysis of thyroid function in df/KO mice is needed.

    It is clear that the interruption of somatotrophic axis (at different levels) is responsible for the smaller body mass, smaller body size and smaller size of different organs, thyroid included, in dwarf mice. In this context, it is worth stressing that IGF-I acts also locally in the thyroid gland, e.g. via enzymes involved in DNA synthesis Furthermore, IGF-I may contribute to thyroid cancers development Therefore, the somatotrophic signaling can also be reduced in this endocrine gland in dwarf mice, what may, presumably, lead to the decrease of the examined thyroid morphological parameters.
    Thyroid Follicles, Various Sizes picture attachment.php?s=6032e1f92c8a7f5848d7823616ffeec3&attachmentid=1313&d=1439059761

    Furthermore, decreased inner follicular surface area and inner follicular perimeter in dwarf mice may suggest smaller amount of colloid in the thyroid gland. It is known that decreased colloid content is observed in hyperthyroidism. In contrast, df/df and GHRKO mice are characterized, as was reported above, by severe (in df/df mice) or mild (in GHRKO mice) thyroid hypofunction. However, one should conclude that results from the present study can not be directly extrapolated into the studies in humans. Even contradictory results have been obtained between experimental studies in humans. For example, whereas decreased oxidative stress was found in dwarf mice huge oxidative damage to membrane lipids was reported in GH-deficient patients the phenomenon which was partially reversed by GH replacement

    Interestingly, both GH and IGF-I increased the iron-induced lipid peroxidation (LPO) in porcine thyroid homogenates [44]. On the other hand, GH and IGF-I may prevent the iron-induced oxidative damage in other tissues . These results suggest that somatotrophic axis may reveal either pro-oxidative or anti-oxidative action, depending on the current redox status. This, in turn, may contribute to the regulation of thyroid growth and function

    The results of the present study are important not only in the context of longevity. There is a strong relationship between thyroid function, GH–IGF-I axis and bone linear growth in animals and humans. It is well known that thyroid hormones are indispensable for bone linear growth. Additionally, untreated hypothyroidism unfavourably affects the results of replacement therapy in GH-deficient patients and also it disturbes the results during diagnosis Thus, further studies, morphological evaluation included, on the thyroid function in subjects with disturbed GH–IGF-I axis would be of great importance.

    Taking into account all above observations, one should hypothesize that GH signaling may contribute to thyroid growth and/or function, and that thyroid function (and/or morphological development) may be somehow affected by somatotrophic axis, although various other factors contributing to the development of thyroid gland are also known.

    Conclusions
    Parameters characterizing thyroid follicle size are decreased in all examined kinds of dwarf mice, which may explain decreased thyroid hormone levels in both basal mutants (Ames df/df dwarfs and GHRKOs). df/df mutation seems to predominate over GHRKO genetic intervention concerning their effects on thyroid growth. Beside TSH, also GH signaling seems to constitute a crucial element in thyroid growth and, possibly, function.

    Competing interests
    The authors declare that they have no competing interests.

    Authors’ contributions
    AG designed and performed the experiment, assessment of thyroid morphological parameters, data analyses and interpretation and wrote the manuscript. MKL supervised preparation of the manuscript and was involved in the interpretation of the results. MMM and AB contributed to the experimental design. MMM, AL and AB were involved in the interpretation of the results and review of the manuscript. All authors read and approved the final manuscript.

    Acknowledgements
    The present study was supported by NIA, AG 19899, U19 AG023122, AG31736, AG032290, The Ellison Medical Foundation, Southern Illinois University School of Medicine and Polish Ministry of Science and Higher Education (N N401 042638).

    The authors would like to thank Dr. Robert G. Struble, PhD (Department of Neurology, Southern Illinois University School of Medicine, Springfield, IL, USA) for his support and advices and for allowing us to use the computerized microscopy analysis system. We also wish to thank Shari Beckman-Randall for technical assistance.

    References:
    http://www.thyroidresearchjournal.com/content/5/1/7











    Last edited by Medical Photos; 08-08-2015 at 06:49 PM.

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