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  • Author: M. I. Noli x
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B. Paier, K. Hagmüller, M. I. Noli, M. Gonzalez Pondal, C. Stiegler and A. A. Zaninovich

ABSTRACT

The effects of cadmium on 5′-deiodination of thyroxine (T4) by rat liver and on the hepatic concentration of non-protein sulfhydryl groups (NPSH) were studied in Wistar rats of 200–250 g body weight. A group of ten rats was injected with cadmium chloride (300 μg/100 g body weight i.p.) daily for 4 days. Another group of six rats received, in addition, dithiothreitol (DTT; 1 mg/100 g body weight i.p.) daily for the same period. A group of eight normal untreated rats served as control. T4 deiodination was also determined in aliquots of liver from untreated rats, with cadmium (2 or 5 mmol/l) and with or without DTT (0, 2·5, 5 or 10 mmol/l) plus 1 μCi 125I-labelled T4. Hepatic NPSH were measured by a colorimetric method employing dithioldinitrobenzoic acid. Homogenates were incubated for 90 min at 37 °C and chromatographed in a tertiary amyl alcohol: hexane: ammonia (2 mol/l) (10: 1: 12) system. Cadmium-injected rats showed a significant (P <0·01) decrease in T4 deiodination and in the generation of 125I (P <0·01) and tri-iodothyronine (T3) (P <0·02). NPSH were also decreased (P <0·02). Administration of DTT restored T4 deiodination and NPSH to normal. In-vitro addition of cadmium or DTT to normal rat liver homogenates induced similar effects on the degradation of T4. Serum concentrations of T4 (P <0·01) and T3 (P <0·01) declined significantly in cadmium-injected rats, whereas DTT administration failed to normalize serum hormone levels. The data suggest that cadmium may have decreased 5′-deiodinating activity through binding to sulfhydryl groups of 5′-deiodinase as it does in other enzymes. The effects on serum T4 concentrations may be unrelated to those on 5′-deiodinase.

Journal of Endocrinology (1993) 138, 219–224

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M A Pavia Jr, B Paier, M I Noli, K Hagmüller and A A Zaninovich

Abstract

The effect of in vivo administration of cadmium chloride on the pituitary-thyroidal axis was assessed in 200 g body weight Wistar rats. A dose of 2·5 mg/kg body weight was injected i.v. 24 h before the experiments were initiated. Plasma thyroxine (T4) and tri-iodothyronine (T3) concentrations in cadmium-treated rats were significantly (P<0·01) decreased, whereas plasma TSH failed to increase in response to low T4 and T3. However, the TSH response to TRH and the pituitary content of TSH in these rats were both normal. Cadmium induced a significant (P<0·01) decrease in 4-h thyroidal 131I uptake and in thyroid/plasma radioactivity ratio. The in vitro conversion of T4 to T3 in the pituitary was significantly (P<0·01) blocked by cadmium whereas there was no in vivo effect. Parameters of peripheral T4 kinetics in cadmium-treated rats, such as metabolic clearance rate (P<0·01), fractional turnover rate (P<0·01), absolute disposal rate (P<0·05), urinary clearance (P<0·05) and faecal clearance (P<0·05), were all decreased by cadmium. The lack of response of TSH to low plasma T4 and T3 and the normal response to exogenous TRH in this and in other non-thyroidal illness syndromes produced by other pathologies suggest a decreased stimulation of pituitary thyrotrophs by endogenous TRH.

Journal of Endocrinology (1997) 154, 113–117

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L F Cageao, M I Noli, I R Mignone, M Farber, C R Ricci, K Hagmüller and A A Zaninovich

Abstract

We have assessed the relative contribution of the thyroid hormones and noradrenaline (NA) on the calorigenic function of brown adipose tissue (BAT) as indicated by GDP binding and O2 consumption of BAT mitochondria. Male Wistar rats of 200 g body weight were made hypothyroid with 131I. Groups of animals were injected s.c., in divided doses, daily for 10 days, with thyroxine (2 μg/100 g body weight) or tri-iodothyronine (T3; 0·3 μg/100 g body weight). Animals were used 7 days after bilateral or unilateral sympathetic nerve excision of BAT (Sx). Sham-operated rats were used as controls. In normal rats kept at 22 °C, GDP binding reached 94 ± 24 pmol/mg protein; untreated hypothyroid rats had normal binding values whereas the T3-treated group showed an increased binding. Sx induced a sharp fall in the three groups (P<0·01). After 24-h exposure to 4 °C GDP binding increased in normal rats to about 410% (P<0·01) whereas binding failed to increase in response to cold in the untreated hypothyroid and the T3-treated groups. Sx reduced GDP binding in the three groups significantly (P<0·01). The consumption of O2 by BAT mitochondria showed similar variations in response to Sx and to cold exposure as did GDP binding. The data indicated that, at room temperature, BAT calorigenesis can function without the thyroid hormones, though not without the catecholamines. The findings in rats exposed to cold showed that the lack of NA was significantly more effective than the lack of thyroid hormones in preventing the BAT hyperactive response. This does not negate an active role for T3 in BAT calorigenesis.

Journal of Endocrinology (1995) 145, 579–584