Iodolactone reproduces some but no all the effects of iodide.

THOMASZ, L; NOSEDA, P; URDINEZ, P; DAGROSA, MA; KRAWIEC, L; PISAREV, MA; JUVENAL, GJ

Buenos Aires

Congreso; 13th International Thyroid Congress.; 2005

Although thyroid gland function is mainly under the control of pituitary TSH, other factors, such as EGF, IGF-1, TGF-b, TGF-a, TNF, etc, may also play a role in this process. Iodine is not used only by the thyroid to synthesize thyroid hormones but also directly influences a number of thyroid parameters such as thyroid proliferation and function. Thyroid autoregulation may be defined as the capability of the intracellular content of iodine to modulate the gland function and its response to other regulation factors. It was shown that, besides thyroid hormones, several iodinated lipids are biosynthesized by the thyroid gland. The aim of this study was to determine the effect of iodine and 6-iodo-5-hydroxy-8,11,14-eicosatrienoic acid delta lactone (IL) on several thyroid parameters. In order to see if the actions of IL were due to the iodide originated from a possible dehalogenation, iodolactone was labeled with 125I. Thyroid bovine follicles were incubated with 125I or 125I-IL during 1 h or 48 h. As it was expected, KClO4 and ouabaine inhibited 125I uptake and MMI inhibited iodine organification. These compounds had no effect neither on 125I-IL uptake or its incorporation to proteins. It is interest to mention that the incorporation of 125I-IL to proteins was almost 95 % (measured as % of TCA precipitable cpm/total cpm). As iodolactone did not dehalogenated under our experimental conditions the effect of KI and IL was assayed on different thyroid parameters. Follicles were cultivated in the presence of TSH, TSH plus KI (10 uM) or IL (10 uM). KI and IL inhibited iodide uptake (C: 100, KI: 53.6 ± 3.8, IL: 56.5 ± 4.5; results are expressed as % from C). There was no effect of both compounds on 125I organification. Total protein synthesis (TPS) was inhibited by both compounds (C: 100, KI: 49.2 ± 3.3, IL: 54 ± 6.5. 35S-methionine was incubated during 1h and TPS was measured as % of TCA precipitable cpm/total cpm. Results are expressed as % from C) Northern blot analysis showed a strong inhibition by iodide of Tg mRNA levels (52 % of control). IL had no effect on this parameter. Iodolactone reproduces some but no all the effects of iodide