Comparative microscopic and electron microscopic study of somatotropic pituitary cells in two rare mammalian species

The aim of this study was to find out the microscopic and ultrastructural features of somatotropic endocrinocytes in two rare mammalian species in postnatal ontogenesis.

Material and methods. We used material from river beavers (Castor fiber L.) and sea otters (sea beaver, Enhydra lutris), listed in the Red Book of the Russian Federation. The collection of material was carried out in the Voronezh Reserve and on the rookeries of marine mammals on the Commander Islands (Bering Island, Medny Island). To fix the material, Shteve, Bouin, and Zenker liquids were used. Paraffin sections were stained with hematoxylin and eosin, aldehyde fuchsin according to Helmi–Dyban. The linear dimensions of cell structures were measured, the cross-sectional area of cells and their nuclei was calculated, and the nuclear cytoplasmic index was calculated. The numerical density of somatotropic endocrinocytes in the field of view was determined. For electron microscopy, pituitary specimens were fixed in 2.5% glutaraldehyde and 1% osmium fixative. Sections were prepared on BS-490 and LKB-4800 ultramicrotomes. Sections were counterstained with uranyl acetate and lead citrate and studied under a Tesla BS-500 electron microscope.

Results. In river beavers and sea otters at the age of 6 months, compared with newborn animals, the number of somatotropic cells in the center of the pituitary gland increases by 3.46 (p<0.05) and 3.32 times (p<0.05), respectively, and in the lateral zones – 2.61 times (p<0.05) and 3.39 times (p<0.05); cell cytoplasm area – 1.96 times (p<0.05) and 1.85 times (p<0.05); the area of the nuclei – 1.48 times (p<0.05) and 1.30 times (p<0.05). In river beavers and sea otters at the age of one year, compared with six-month-old animals, an increase in the number of somatotropic cells in the center of the pituitary gland by 1.27 times (p<0.05) and 1.33 times (p<0.05) was revealed; and in the lateral zones by 1.08 times (p<0.05) and 1.02 times (p>0.05); and area of the cytoplasm of cells, respectively – 1.29 times (p<0.05) and. 1.25 times (p<0.05). The maximum indicators of secretory activity of somatotropic cells were found in river beavers and sea otters at the age of 1 year.

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