Thyroid function and deiodinase activities in rats with marginal iodine deficiency

Thyroid hormones are extremely important for development of the fetal central nervous system. Thyroidectomy results in severe hypothyroidism. In this study two levels of maternal hypothyroidism were reached by administration of different amounts of thyroxine (T 4 ) and 3,5,3 0 -tri-iodothyronine (T 3 ) to thyroidectomized pregnant rats. We examined the production, distribution and transport of T 4 and T 3 by performing a kinetic experiment (three-compartment analysis) with intact and thyroidectomized near-term pregnant rats which received either very low (Tx þ lowTH) or normal (Tx þ TH) doses of T 4 and T 3 . Despite administration of normal doses of thyroid hormones, plasma TSH was still elevated in the Tx þ TH rats, meaning that these rats were still mildly hypothyroid. The Tx þ lowTH rats were markedly hypothyroid, the plasma T 4 and T 3 levels being very low. In the mildly hypothyroid rats the transport of T 4 from plasma to the fast pool and vice versa was decreased compared with intact near-term pregnant rats. This could imply that much less T 4 is transported to the feto-placental compartment. Liver type I deiodinase was decreased, resulting in lowered plasma T 3 values. In the markedly hypothyroid rats all pools and rates of transport of T 4 and T 3 were greatly decreased. In conclusion, even mild hypothyroidism, despite normal plasma T 4 values, results in significant changes, especially in maternal T 4 transport. We suggest that even mild maternal hypothyroidism will have a negative effect on the availability of maternal T 4 for fetuses.

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“…The determination of type I deiodinase (ID-I) activity in liver homogenates was performed by the method described by Janssen et al (25).…”

Section: Analytical Determinationsmentioning

confidence: 99%

Maternal thyroxine and 3,5,3'-tri-iodothyronine kinetics in near-term pregnant rats at two different levels of hypothyroidism

Versloot

Heide²,

Elst³

et al. 1998

European Journal of Endocrinology

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“…Janssen et al (24) found no effect of iodine deficiency on hepatic ID-I activity, even though T 4 in their animals was lower. In the brain an increase in ID-II was found in iodine-deficient rats (24).…”

Section: Discussionmentioning

confidence: 74%

“…In the brain an increase in ID-II was found in iodine-deficient rats (24). In our study MID induced an PCR, plasma clearance rate; PR, production rate; V, plasma equivalent distribution volume; Q, pool quantity; TRpf, TRfp, TRps, and TRsp, rates of transport between plasma and the fast and slow pools respectively, in each direction; DRfo and DRso, disposal rate from fast and slow pool respectively; p, plasma; 2, fast pool; 3, slow pool.…”

Section: Discussionmentioning

confidence: 93%

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Effects of marginal iodine deficiency on thyroid hormone production, distribution and transport in nonpregnant and near-term pregnant rats

et al. 1998

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During pregnancy maternal thyroid hormones are of great importance for normal development of the central nervous system of the fetus. Iodine deficiency of the mother can result in an impaired development of the fetal brain. In large areas of the world iodine intake is moderately low. To study the effects of marginal iodine deficiency (MID) on the production, distribution, and transport of thyroxine (T 4 ) and 3,5,3 0 -tri-iodothyronine (T 3 ) in nonpregnant and near-term pregnant rats we performed kinetic experiments (three-compartment analysis). Despite unchanged plasma T 4 and T 3 during MID, the production and plasma clearance rates of T 4 decreased 30% (P = 0.01) in MID nonpregnant (MID-C) rats. For T 3, the plasma clearance rate was increased 70% (P = 0.046), while the T 3 production was more than doubled (P = 0.042) in MID-C rats. In MID near-term pregnant rats T 3 production was decreased 20% (P = 0.04). Hepatic deiodinase type I activity increased during MID in both nonpregnant and pregnant rats. It appears that during MID, rats are able to maintain their euthyroid status. The pronounced increase in transport of T 4 from plasma to the fast pool observed in pregnant rats on a normal iodine diet did not occur during MID. In conclusion, in rats MID affects maternal thyroid hormone metabolism, thus influencing the availability of maternal T 4 for the fetus. European Journal of Endocrinology 138 713-718

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“…The HuNa group showed significantly higher concentration of triiodothyronine (2.00 vs. 1.41 nmol/l; P < 0.05) and nonsignificantly lower thyroxine and iodine concentrations in blood serum (Figure 1). This decrease in blood serum concentrations of T 4 and iodine accompanied by an increase in T 3 concentration is indicative of an insufficient supply of iodine to the thyroid gland (Janssen, 1994) which then prefers the synthesis of the less iodine-demandingT 3 at the expense of T 4 . This findings indicates possible anti-thyroid activity of HuNa and supports the data of Huang et al (1994) who demonstrated a significant increase in T 3 and a decrease in T 4 concentrations in blood serum of rats fed a low-iodine diet containing humine substances.…”

Section: Resultsmentioning

confidence: 99%

Effects of humine compounds on iodine utilisation and retention and on the function of the thyroid gland

Herzig¹,

Písaříková²,

Kursa³

et al. 2001

Vet. Med. - Czech

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Effects of sodium humate (HuNa), containing 61.9% of humic acids in dry matter, on utilisation and retention of dietary iodine were investigated in balance experiments carried out in pigs. A control group was fed a commercial diet containing 0.1 mg of iodine per kg. The daily intake of iodine was 129.2 µg per animal or 4.08 µg per kg live weight. The recommended intake of dietary iodine is 0.25 to 0.30 mg per kg at 88% dry matter. The experimental group (HuNa) was fed the same diet supplemented with 3% of sodium humate which contained 0.5 mg of iodine per kg at 90.04% dry matter. The supplementation increased the daily intake to 141.4 µg per animal, or 4.45 µg per kg live weight. The supplementation of HuNa increased significantly the amount of iodine excreted in faeces (53.2 ± 11.0 vs. 43.0 ± 6.47 µg per animal per day; P < 0.05) and nonsignificantly the urinary iodine excretion (31.8 ± 8.93 vs. 29.0 ± 11.3 µg per animal per day). Differences between the HuNa and the control groups in blood serum iodine concentrations (18.8 vs. 18.1 µg per litre) and urinary iodine concentrations (32.5 vs. 34.4 µg per litre) were nonsignificant. It is evident from the concentrations that the pigs suffered from a serious iodine deficiency. Compared with controls, the HuNa group showed significantly higher triiodothyronine concentration (P < 0.05) and nonsignificantly lower thyroxine and iodine concentrations in blood serum. Dietary iodine utilisation was lower in the HuNa than in the control group (62.3 vs. 66.6%). The results show that utilisation of dietary iodine was limited and that sodium humate (humic acids) reduced iodine utilisation and retention and affected also other parameters indicating their goitrogenic effects.

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Thyroid function and deiodinase activities in rats with marginal iodine deficiency

Cited by 17 publications

References 19 publications

Maternal thyroxine and 3,5,3'-tri-iodothyronine kinetics in near-term pregnant rats at two different levels of hypothyroidism

Maternal thyroxine and 3,5,3'-tri-iodothyronine kinetics in near-term pregnant rats at two different levels of hypothyroidism

Effects of marginal iodine deficiency on thyroid hormone production, distribution and transport in nonpregnant and near-term pregnant rats

Effects of humine compounds on iodine utilisation and retention and on the function of the thyroid gland

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