Search

We measured the activities of iodothyronine-activating (D1 and D2) and -inactivating (D3) deiodinases, as well as the circulating levels of their corresponding substrates and/or products, T4 ,T 3 ,a nd rT 3, in the developing rainbow trout. The study was conducted through 20 consecutive months and included fry, fingerlings, and mature animals from 14 to 88 weeks post-hatching (ph). Initially, blood concentration of active iodothyronines was low and tissue D3 activity was greater than the activity of D1 and D2. As fry developed into fingerlings, the activity of liver D2 increased, while that of skin D3 declined. The time course of these changes was directly (T3) or inversely (rT3 and D3) correlated to an increase in age, length, and body weight. The initial increment in both circulating T3 and hepatic D2 activity during the first spring (March-April; weeks 46–50 ph) coincided with the onset of gonadal differentiation, whereas the highest values of T3 and hepatic D1 and D2 (September–October; weeks 70–74 ph) occurred at the onset of sexual maturity. These results suggest that a hepatic supply of active T3 is temporally associated with gametogenesis. Abbreviations: ANS – 8-anilin-1-naphthalene sulphonic acid; DTT – Dithiothreitol; ph – post-hatching; T4 – thyroxine; T3 – triiodothyronine; rT3 – reverse triiodothyronine; T2 – diiodothyronine.

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.