Iodine Metabolism in Response to Goitrogen Induced Altered Thyroid Status Under Conditions of Moderate and High Intake of Iodine

Abstract

Metabolic experiments in rats were undertaken to relate excretory pattern of iodine and thiocyanate, with thyroid weight and the circulating levels of thyroxine, in response to moderate and high intake of iodine and under conditions of goitrogen induced altered thyroid status. On a moderate intake of iodine (by depriving diet of KI) 25 mg of thiocyanate or substitution of 1/3rd proportion of casein based diet with dry cabbage, could significantly reduce plasma thyroxine level by 60 days. Neither body weight nor the weights of liver, kidney, heart or spleen were affected due to exposure to goitrogens. A significant increase in thyroid weight as well as higher excretion of iodine and thiocyanate were evident in goitrogen-fed rats. Presence of high amounts of KI, to a certain extent, offered protection from adverse effects of the goitrogens. Semi quantitative assessment of thyroid, indicated hypofunctioning of thyroid with follicular hyperplasia in thiocyanate fed rats. These alterations were of moderate degree in response to cabbage feeding. These results emphasize that, moderate intake of iodine, adequate to meet iodine requirement, may not ensure normal functioning of thyroid in the presence of goitrogens.

Long-Term Dietary Iodine Deficiency Alters Transport of 2-Deoxy-D-Glucose across the Adult Rat Blood-Brain-Barrier.

“…Our observations that feeding an iodine-deficient (LIT) diet to weanling rats for 8 weeks (short term) did not affect their body or brain weight, and induced only a modest hypothyroidism are in line with some recent observations made in thiocyanate-fed rats [14,18] as well as with those of McIntosh et al [19]. They probably suggest that the duration of feeding was not sufficient enough to affect these parameters in the rats.…”

Effect of cassava (<i>Manihot esculenta crentz</i>) on thyroid status under conditions of varying iodine intake in rats

“…Diet deprived of iodide but rich in thiocyanate, glucosinolate lowers the circulating level of thyroxine (T4) and triiodothyronine (T3) in rats (Papas et al 1979;Lakshmy et al 1995). Intake of cassava decreased the serum total T4 and T3 level significantly.…”

The nutritional significance, biosynthesis and bioavailability of glucosinolates in human foods

“…Both thiocyanate ions, and oxazolidine‐2‐thiones formed from glucosinolates with an aliphatic side‐chain containing a beta‐hydroxy group, are goitrogenic, although the mechanisms of action are different. Thiocyanate ions are iodine competitors, and therefore in both pigs16, 17 and rats18 their goitrogenic effects can be mitigated to some extent by increasing the level of iodine in the diet. On the other hand 5‐vinyloxazolidine‐2‐thione is thought to be a direct inhibitor of thyroxine synthesis, an effect which is independent of iodine availability.…”