The effects of 17β-estradiol injections on thyroid hormone deiodination pathways in liver and other tissues of female and male rainbow trout (Oncorhynchus mykiss) at different stages of sexual maturity

摘要

The effects of two intraperitoneal injections of 17(3-estradiol (E_2) over 7 days were studied on thyroid hor- ' mone plasma levels and on activities of thyroxine (T_4), 3,5,3 '-triiodothyronine (T_3), and 3,3',5'-triiodothyronine (rT3) outer-ring deiodination (ORD) and inner-ring deiodination (IRD) pathways in various tissues of female and male rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)). E_2 administered to adult females and males at different stages of sexual maturity increased livermass, depressed plasma T_3 levels with no change in plasma T_4 levels, and severely decreased liver T_4ORD activity. E_2 also modestly depressed hepatic rT_3ORD activity, but only at low substrate levels, and had no consistent effect on the hepatic IRD pathways. There were no E_2-induced changes in brain, gill, or heart deiodination, but E_2 increased kidney T_3IRD activity. In contrast, an all-female stock of trout with rudimentary ovaries responded to E_2 with an increase in liver mass but without change in plasma T_4 and T_3 levels or liver and brain deiodination activities. In conclusion, the decrease in plasma T_3 levels in both male and female adult E_2-injected trout may be due to both decreased hepatic T_3 production and increased renal T_3 degradation. However, thyroidal responses to E_2 depend on physiological/developmental state and were absent in a highly immature all-female trout stock.