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In this study we analyzed whether corticosterone synthesis is involved in the regulation of adrenal gland type II deiodinase (AG-D2) activity during acute cold exposure. Two well-known inhibitors of steroidogenesis, aminoglutethimide (AGT) and metyrapone (MTP), were administered to male Wistar rats maintained either at room temperature or acutely exposed to cold (1 h at 4°C). AG-D2 activity was measured by the radioiodide release method, and corticosterone circulating levels were measured by competitive protein binding assay. Results show that resting corticosterone levels and AG-D2 activity were lower in both AGT-and MTP-treated rats. Furthermore, the phasic increase normally exhibited by AG-D2 activity in response to acute cold stress was blunted in AGT-and MTP-treated animals. Therefore, we conclude that corticosterone synthesis is necessary in preserving the physiologic response of Ag-D2 activity to cold exposure.

We determined the kinetic parameters as well as the fractional turnover rate (FTr) and half-life (t(1/2)) of rat adrenal gland 5'deiodinase activity (AG-5'D). Adrenal glands from male euthyroid or surgically thyroidectomized (Tx) Wistar rats were homogenized (HEPES, 10MM: ; pH 7.5; sucrose, 0.25M: ; EDTA 1MM: ) and centrifuged at 10,000g for 15 min at 4°C. The resulting crude microsomal supernatants were used for ail measurements of 5'D activity. Using rT(3) (2-500NM: ) the true Km and the Vmax values were of 20.2NM: and 289 fmol of I(-) release/mg protein/h. With T(4) as substrate these values were 5.8NM: and 622 fmol/h/mg protein. Protein inhibitor (cycloheximide 6 mg/100 g wt) administration allowed to determine an FTr of 0.68 h(-1) and a t(1/2) of 1.01 h. Results demonstrate that the greatest 5'D activity in the rat adrenal gland corresponds to isotype II, because the reaction is GTG and PTU-resistant (70-80%), accepts T(4) as a far better substrate than rT(3) (17-fold) and the former thyronine has a 50-90% inhibitory concentration in the 4-100NM: range. Furthermore, rats thyroidectomized for 5 and 15 days showed a conspicuous increase in cerebral cortex and adrenal 5'D-II activity. These characteristics as well as the rapid FTr and short †(1/2) are shared by type II 5'D present in rat pineal, pituitary and brain.

Type II 5′ deiodinase (5′D-II) activity was assessed in the hypothalamus (HP), pituitary (PIT), and adrenal gland (AG) of adult male rats after two different photoperiodic regimes: (1) cyclic light-dark conditions (LD, 12∶12) or (2) 4 days in continuous darkness (DD). Under cyclic LD conditions HP, PIT and AG 5′D-11 activity showed a significant circadian rhythm (P

The present study analyses the activity of 5′deiodinases type I and II in mammary gland during the breeding and estrous cycle of the rat, and includes indirect evidence that 5′D-I is present only in the alveolar epithelium. Data show that the mammary gland exhibits 5′D-II activity throughout the developmental period and its activity varies along the allometric growth of the gland. 5′D-I is detected during the differentiation stages of the alveolar epithelium (puberty, late pregnancy) and its activity rises significantly (10-fold) 24 h after delivery. Data also show that 5′D-I activity is not present in the fat pads of the gland. These findings suggest that during its differentiation and functional stages, the mammary gland requires an elevated and compartmentalized production of T3.