Acute inhibitory effect of excess iodide on ornithine decarboxylase in the thyroid of propylthiouracil-treated rats

Abstract

Polyamines such as putrescine, spermidine and spermine have been thought to play an important role in thyroid growth induced by goitrogens. Reduced biosynthesis of these polyamines might play a role in the antigoitrogenic effects of excess iodide. This study was designed to examine the effect of potassium iodide (KI) on ornithine decarboxylase (ODC), a rate-limiting enzyme in the biosynthesis of polyamines. Thyroidal ODC activity, protein content and mRNA were increased in rats made hypothyroid by 10 days of propylthiouracil treatment. The increase in ODC activity was suppressed after subcutaneous injection of KI (13mg/kg body weight); the apparent half-life of ODC activity after the treatment was estimated to be 19 min and the maximum suppression (90%) was seen 60 min after the treatment. On the other hand, administration of iodine-containing compounds including L-thyroxine, L-di-iodotyrosine,amiodarone, iopanoic acid and erythrosine showed no significant effect on ODC activity. The inhibitory effect of excess iodide was not reversed by pretreatment with dibutyryl cAMP and theophylline. The amount of immunoreactive ODC protein was reduced by iodide treatment (40%). However, the decrease was not as great as the decrease in ODC activity (90%). No significant change in thyroidal ODC mRNA content was seen 1 and 3 h following KI treatment. These results suggest that excess iodide reduces ODC activity in the rat thyroid gland by a post-transcriptional mechanism.

A Tear Metabolomic Profile Showing Increased Ornithine Decarboxylase Activity and Spermine Synthesis in Thyroid-Associated Orbitopathy

“…Our results show an increase in the concentration of spermine in active TAO tears, with spermidine not being measurable in our study and putrescine showing only a trend toward increased concentration (p = 0.061). It is known that, in rats, thyroid ornithine decarboxylase is strongly stimulated by TSH [15,16], leading to increased levels of polyamines with a proliferative role in goiter and tumor formation [17,18]. As orbital fibroblasts themselves possess their own TSH receptors, playing a pathophysiological role in TAO, the increased synthesis of spermine could also be directly related to the overstimulation by Graves' autoantibodies and could play a proliferative role at the origin of the increased myogenesis and adipogenesis observed in orbitopathy.…”

Comparison of the Effects of 3,5,3'-Triiodothyroacetic Acid and Triiodothyronine on Goiter Prevention and Involution and on Hepatic and Skeletal Parameters in Rats

“…ODC is the first and rate-controlling enzyme in the biosynthesis of polyamines. Polyamines such as putrescine, spermidine and spermine have been thought to play an important role in thyroid growth induced by goitrogens [32]. ODC activity in the rat thyroid is induced by TSH [33,42,43].…”

“…Ornithine decarboxylase (ODC) is the rate-limiting enzyme in the biosynthetic pathway of polyamines which have been thought to play an important role in thyroid growth induced by goitrogens [32]. Therefore, we thought it of interest to compare the effect of TRIAC and T 3 on the activity of ODC.…”

Anabolic effects of rhIGF‐I/IGFBP‐3 in vivo are influenced by thyroid status

“…The animals were adapted in four groups of eight with free access to chow and water on a 12-h light : dark cycle for 14 days prior to experimentation. Two groups of animals were then given propylthiouracil (PTU; Sigma, St Louis, MO, USA, 0´1% final concentration) in the drinking water for 10 days to produce hypothyroidism [16], and remained on PTU treatment during the 6-day experimental period. During the 6-day experimental period access to food in all groups was restricted to 25% of the amount of food consumed by freely fed rats.…”