Study of hypervitaminosis E in the chick
Creators: name: Wong, Fook Chuen
Publisher: name: University of British Columbia
Year: 2011

description: A study was made of the effects of feeding excess vitamin e to chicks. Three groups of experiments were conducted to investigate (1) thyroidal response to excess vitamin e, (2) respiration rate of muscle mitochondria from chicks fed excess vitamin e; and (3) symptoms of hypervitaminosis e. In two separate experiments, chicks were fed normal and excess levels (220 i.u./kg. of diet) of vitamin e and were subjected to temperatures of 14.5 and 31.5°c. the goitrogenic effect of thiouracil on the birds in the different treatments was measured. At both temperatures the thiouracil-treated chicks fed excess vitamin e exhibited a lesser enlargement of the thyroid glands than did chicks receiving a normal level of vitamin e. This finding indicates a reduction in the secretion of thyroid stimulating hormone (tsh) in birds fed excess vitamin e. the level of vitamin e which was fed did not affect the growth rate or feed consumption at either temperature. It, therefore, appears that the metabolic rates of the chicks fed the low and excess levels of vitamin e were similar despite differences in thyroid activity and that tissue respiration in birds fed excess vitamin e can be maintained with a reduced supply or turnover of thyroid hormone. The activity of the thyroid gland itself was studied in response to excess vitamin e in another experiment. Using radioiodine (l¹³¹) as a tracer, it was found that the rates of iodine uptake and release by the thyroid gland were both slower in birds fed excess vitamin e (220 i.u./kg. 0f diet) than in control birds. Because vitamin e acts as a biological antioxidant, it may, in excess amounts, depress the rate of oeiodination of thyroxine in the peripheral tissue at which thyroid hormone is removed from the circulation. As a consequence, the secretion of tsh would be reduced. In order to obtain some indication of cause and effect in the mechanism by which the excess vitamin e affects thyrotropic hormone secretion rate and thyroid activity, the respiration rate of mitochondria isolated from the pectoral muscle of chicks which had been fed excess vitamin e (2200 i.u./kg. 0f diet) was compared with that of the control birds. The results showed a significant reduction in oxygen uptake by the muscle mitochondria of chicks fed the excess amount of vitamin e. The growth rate of the chicks fed the excess level of vitamin e in this experiment was markedly lower than that of the control chicks. It is suggested that the chick may maintain a normal respiration rate when fed excess vitamin e up to a certain level through a reduction in thyroid activity. With a large excess of vitamin e, however, no further compensation is possible. and respiration rate is depressed below normal. Excess vitamin e caused hypoprothrombinemia, indicative of vitamin k-deficiency. Other symptoms noted were a reduction in hematocrit values, reticulocytosis and an abnormally fluid appearance of the bone marrow. Based upon observations of bone calcification, the calcium requirement appeared to be increased in the presence of excess vitamin e.