Edward
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Recently, we described a two-pool model for 3,5,3'-triiodothyronine uptake and metabolism in the isolated perfused rat liver. Here, we applied this model to investigate transmembrane thyroxine (T4) transport and its possible ATP dependence in vivo. These studies are performed in perfused rat livers during perfusion with or without fructose in the medium, as it has been shown that intracellular ATP is decreased after fructose loading. Furthermore, we studied serum T4 tracer disappearance curves in four human subjects before and after intravenous fructose loading. In the perfused rat liver, we found a decrease in liver ATP concentration and a decrease in medium T4 disappearance and T4 uptake in the liver pool after fructose. Furthermore, it was shown that, when corrected for differences in the medium free hormone concentration, only transport to the metabolizing liver pool was decreased after fructose perfusion, whereas uptake in the nonmetabolizing pool was unaffected. Disposal, corrected for differences in transport into the metabolizing pool, was also not affected after fructose. In the human studies, intravenous fructose administration induced a rise in serum lactic acid and uric acid, indicating a decrease in liver ATP. This was observed concomitant with a decrease in serum tracer T4 disappearance during the first 3 h after fructose administration. These results suggest ATP dependence of transport of iodothyronines into the liver in vivo and show that, in the rat liver and in humans, uptake of T4 may be regulated by intracellular energy stores; in this way the tissue uptake process may affect intracellular metabolism and bioavailability of thyroid hormone.
De Jong, M., Docter, R., Bernard, B. F., Van Der Heijden, J. T., Van Toor, H., Krenning, E. P., & Hennemann, G. (1994). T4 uptake into the perfused rat liver and liver T4 uptake in humans are inhibited by fructose. American Journal of Physiology, 266, E768–E775.
Four groups of 6 rats were given ad libitum diets with over 60% of the energy as sucrose, fructose or glucose for 10 weeks, and were compared to animals given chow. Assessment of thyroid activity was made using metabolic rate, thyroid 123I uptake, and serum thyroid fraction measurement before, after 5 and 10 weeks on the diet, and 6 weeks after return to a control diet. The major effects were that the thyroid 123I uptake was significantly less than control in the rats after 10 weeks on a high carbohydrate diet. Only the animals on the fructose diet showed any consistent and significant falls in serum T3 and FT3, and T4. These findings suggest that the type of dietary carbohydrate may affect thyroid function in rats.
Macdonald, I. (1989). Some effects of various dietary carbohydrates on thyroid activity in the rat. Annals of nutrition metabolism, 33, 15–21.
Notes:
There is a good chapter in Wolfgang Lutz's book "Life without Bread" called "Carbohydrates and Hormones" where Dr. Lutz describes different catabolic and anabolic effects of dietary components and in an earlier chapter ATP production.
The mechanisms which were based on German experiments done on carbohydrate metabolism on warm blooded animals were somewhat neater and more clear than some of the other mechanisms that have been described.
Thyroid hormone regulates fatty acid metabolism, this has been demonstrated in hyperthyroid studies where fatty acids are oxidized at an accelerated rate.
De Jong, M., Docter, R., Bernard, B. F., Van Der Heijden, J. T., Van Toor, H., Krenning, E. P., & Hennemann, G. (1994). T4 uptake into the perfused rat liver and liver T4 uptake in humans are inhibited by fructose. American Journal of Physiology, 266, E768–E775.
Four groups of 6 rats were given ad libitum diets with over 60% of the energy as sucrose, fructose or glucose for 10 weeks, and were compared to animals given chow. Assessment of thyroid activity was made using metabolic rate, thyroid 123I uptake, and serum thyroid fraction measurement before, after 5 and 10 weeks on the diet, and 6 weeks after return to a control diet. The major effects were that the thyroid 123I uptake was significantly less than control in the rats after 10 weeks on a high carbohydrate diet. Only the animals on the fructose diet showed any consistent and significant falls in serum T3 and FT3, and T4. These findings suggest that the type of dietary carbohydrate may affect thyroid function in rats.
Macdonald, I. (1989). Some effects of various dietary carbohydrates on thyroid activity in the rat. Annals of nutrition metabolism, 33, 15–21.
Notes:
There is a good chapter in Wolfgang Lutz's book "Life without Bread" called "Carbohydrates and Hormones" where Dr. Lutz describes different catabolic and anabolic effects of dietary components and in an earlier chapter ATP production.
The mechanisms which were based on German experiments done on carbohydrate metabolism on warm blooded animals were somewhat neater and more clear than some of the other mechanisms that have been described.
Thyroid hormone regulates fatty acid metabolism, this has been demonstrated in hyperthyroid studies where fatty acids are oxidized at an accelerated rate.