Journal article

Publication year: 1996

Pages: 271-278

Journal: Journal of Animal Physiology and Animal Nutrition

Volume number: 75

Issue number: 4-5

ISSN: 0931-2439

DOI Link: https://doi.org/10.1111/j.1439-0396.1996.tb00492.x

Publisher: Wiley

Abstract: 
This study was performed to investigate the effect of zinc deficiency on thyroid-hormone metabolism. Therefore, two experiments with growing male Sprague-Dawley rats were carried out. In both experiments, all the rats were fed sufficient quantities of diet by gastric tube in order to avoid the confounding effects of low food intake in zinc-deficient individuals. In the first experiment, the zinc concentration of the diet (0.5 mg Zn/kg vs 30 mg Zn/kg) and the dietary fat (coconut oil/safflower oil mixture, 7:1 vs linseed oil) were varied. In the second experiment, rats were fed zinc-adequate (40 mg Zn/kg) or zinc-deficient (0.5 mg Zn/kg) fat-free diets for 6 days. After that period, the groups were divided; half the rats were given the fat-free zinc-adequate and zinc-deficient diets for another 3.5 days, whereas the other half was given the same diets supplemented with 5 % safflower oil. In both experiments, the rats fed the zinc-deficient diets showed reduced body-weight gain and markedly reduced activity of alkaline phosphatase and zinc concentration in serum, proving their severe zinc-deficient states. In both experiments, zinc deficiency caused hypothyroidism, characterized by reduced concentrations of triiodo-thyronine (T-3) and total and free thyroxine (T-4) in serum, regardless of the dietary fat. However, in the first experiment the reduction of T-3 concentrations by zinc deficiency was more pronounced in the rats fed the diet with predominantly coconut oil than in the rats fed the diet with linseed oil, meaning that the type of dietary fat might influence the effect of zinc deficiency on thyroid-hormone metabolism. The activity of hepatic thyroxine 5' monodeiodinase (5'D) determined in the second experiment was markedly elevated by zinc deficiency, regardless of the dietary fat level. The dietary fat also influenced the concentration of thyroid hormones. In the first experiment, the rats fed the diet with predominantly coconut oil had higher concentrations of T-3 and lower concentrations of T-4 than the rats fed the diet with linseed oil, whereas there was no difference in the concentration of free T-4 between both groups. In the second experiment, supplementation of 5% safflower to the fat-free diet increased the concentration of T-3, whereas the concentrations of total and free T-4 remained unchanged by safflower-oil supplementation. In conclusion, this study shows that both the zinc supply and the dietary fat influence thyroid-hormone metabolism. This might be of physiological significance, because thyroid hormones mediate important physiological processes.

Harvard Citation style: Eder, K. and Kirchgeßner, M. (1996) Zinc deficiency and the concentrations of thyroid hormones in serum of force-fed rats, Journal of Animal Physiology and Animal Nutrition, 75(4-5), pp. 271-278. https://doi.org/10.1111/j.1439-0396.1996.tb00492.x

APA Citation style: Eder, K., & Kirchgeßner, M. (1996). Zinc deficiency and the concentrations of thyroid hormones in serum of force-fed rats. Journal of Animal Physiology and Animal Nutrition. 75(4-5), 271-278. https://doi.org/10.1111/j.1439-0396.1996.tb00492.x