Effects of short-term 17β-estradiol treatment on the properties of t3-binding proteins in the plasma of immature rainbow trout,salmo gairdneri

✍ Scribed by Cyr, Daniel G. ;Eales, J. G.

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 610 KB
• Volume: 252
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402520306

✦ Synopsis

To determine the effects of 17P-estradiol (E,) on the properties of the plasma proteins that bind 3,5,3'-triiodo-L-thyronine (T3), immature rainbow trout, Salmo gairdneri, were intraperitoneally injected on days 0 and 3 with 0.5 mg E2-3-benzoateI100 g body weight, and plasma was sampled on days 4, 7, or 12. Control trout received peanut oil alone. E, increased significantly the proportion of [ lz5I1T3 bound to plasma-binding sites. Separation of plasma proteins of control trout by agarose filtration on Bio-Gel A-1.5 m revealed that T3 bound to two main sites corresponding to molecular weights of 130 kDa (presumed prealbumin) and 55 kDa (presumed Pglobulin). Addition of a calculated amount of unlabeled T3 displaced 112511T3 from the 55 kDa site, indicating its role as the T3 high-affinity and low-capacity site. E, treatment initiated production of vitellogenin, which did not bind T,. Saturation analysis of [lZ5I]T3 binding conducted on miniature G-25 Sephadex columns indicated that E2 increased the capacity of the low-affinity, high-capacity T3-binding site without effect on the high-affinity, low-capacity T,-binding site. In conclusion, T, binds to two main plasma sites and E, causes an increase in the capacity of the low-affinity site, resulting in a decrease in free T3 and in possible changes in T3 availability to tissues.

In certain mammals, 17p-estradiol (E,) increases hepatic synthesis of thyroxine-binding globulin (TBG) , responsible for binding Lthyroxine (T4) and 3,5,3'-triiodo-L-thyronine (T3) in the plasma (Oppenheimer, '68; Chopra, '75;