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Interrelation between thyroid function and vitamin A in avian metabolism Coates, Viona


Three approaches were made to study the interrelations between thyroid function and vitamin A in avian metabolism. These were a histological assessment of the activity of the thyroid gland as it is affected by hypervitaminosis A, the effect of hypervitaminosis A on the incubation time of eggs injected with different levels of vitamin A alcohol and palmitate, and finally the effects of hypervitaminosis A on thyroidal uptake and release of radioiodine by chickens. These studies yielded the following observations. CI) Histological -measurements indicated that dietary hypervitaminosis A can depress the secretion of thyroid stimulating hormone. (2) The effect of hypervitaminosis A on thyroid activity as affected by environmental temperature. (3) Vitamin A palmitate and alcohol prolong incubation time. The alcohol form has, in addition, an adverse effect on embryonic development which is manifested in hemorrhaging and malformation of the embryo. (4) Vitamin A in excess may either depress or stimulate thyroidal uptake of radioiodine depending upon an unidentified component of the environment. (5) Vitamin A in excess affects the endocrine system. This is indicated by an increase in size of the thyroid and adrenal glands and a decrease in size of combs and testes.

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