Restorative Processes in the Thyroid Gland of Russian Long-Haired Rams in Postnatal Ontogenesis

The aimof this study is to study the recovery processes in the thyroid gland of Russian long-haired sheep in postnatal ontogenesis.

Material  and  methods. The  material  for  the  study  was  77  rams  of  the  Russian  long-haired  breed  of various ages. Fragments of the thyroid gland were fixed in a 10% solution of neutral formalin, in liquids of Shtive and Buena. Thin paraffin sections with a thickness of 4–5 μm were stained with hematoxylin and eosin, azan according to Heydenhein, and the PAS-reaction was applied. The average area of all follicles in the field of view was determined at a magnification of ×80 (ob. 10; oc. 8) using G.G. Autandilov ocular grid (50 fields of viewfor each animal). Based on the obtained absolute values of the area of the follicles and the interfollicular epithelium (mm 2 ), the relative value (%) of the area of the follicles and the interfollicular epithelium was determined. Using a screw eyepiece micrometer, the diameter of the nuclei of thyrocytes in the follicles and thyrocytes of the interfollicular epithelium was measured. The area of the nuclei was determined by the diameter of the nuclei. The mitotic index (MI) in ‰ was calculated . The number of dividing cells per thousand thyrocytes was calculated. At  least 20,000 cells were counted for each animal.

Results.It was found that in rams aged 15 days, the area of interfollicular epithelium was 86.5%, microfollicles occupied an area of 13.5%. Dividing cells were common, with the MI of follicular and interfollicular thyrocytes being 0.19‰. In rams at the age of 2 months, the number of small follicles increased, the areaof which was 19.7%. MI in follicles increased to 0.21‰, in interfollicular epithelium it decreased to 0.16‰. In rams at the age of 4 months, the area of follicles almost doubled, the area of interfollicular epithelium decreased by 16.1%. In rams aged 2–3 years, the area of interfollicular epithelium decreased, while MI decreased and was 0.13‰ in 3-year-old animals. In rams at the age of 4 and 5 years, there was a decrease in the functional activity of thefollicles. MI in large follicles was higher than in small follicles (0.12–0.13‰ versus 0.09‰).

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