DEPOSITION OF THYROID HORMONES IN THE BIRD EGGS AND IMPACT ON EMBRYO DEVELOPMENT
А. V. Gunchak, І. B. Ratuch
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Institute of Animal Biology NAAS, str. Stus, 38, Lviv, 79034, Ukraine
The article reviews the latest knowledge about the possibility of thyroid hormones deposition in the bird eggs. According to data of scientific literature, thyroid hormones (TH) are present in the eggs and localized mainly in the egg yolks. Other researchers declare that thyroid hormones in the chicken eggs white no guest at all. At the same time, it is proved that during egg incubation the absorption of radioactive iodothyronines by oocytes yolk from vascular system occurs.
Using of maternal thyroid hormones reserves during bird embryonic development is confirmed by disappearance of yolk hormones during incubation that testified transport of thyroid hormones into embryos. This mechanism of thyroid hormones transportation is caused to the fact that at the first days of the incubation the thyroid gland of embryos does not secrete the hormones although they are necessary in this period because playing an important role in the differentiation and maturation of embryos tissues. Indirect studies indicate that thyroid hormones are transported into oocyte by binding with lipoproteins and transthyretin via receptor-mediated mechanisms. Associated with lipoproteins of yolks the thyroid hormones may pass from yolk into embryo by means of non specific endocytosis or can be transported by using the special carrier. Believed, that thyroid hormones are overpasses into oocyte due to energy-dependent process with using of carriers, or by passive diffusion into the cells after dissolving in the lipids of plasma membrane.
Thyroid hormones level in the eggs and, consequently, the functional activity of the thyroid gland during pipping period depends on the functional state of maternal thyroid gland.
However, attention is drawn to the fact that thyroid hormones reserves of yolk play a role in early embryonic period of birds (e.g. in regulation of brain morphogenesis). Main source of thyroid hormones for chick embryos at 13.5; 14.5 and 16.5th days of incubation are hormones from their own thyroid gland.
Important role of thyroid hormones in the metabolism of carbohydrates and fats, acceleration of protein synthesis, stimulation the growth and cellular differentiation of the embryo have reviewed in the article.
Keywords:THYROID HORMONES, EMBRYO, YOLK, POULTRY, INCUBATION
