Effects of short-term 17β-estradiol treatment on the properties of T4-binding proteins in the plasma of immature rainbow trout,Oncorhynchus mykiss

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

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 574 KB
• Volume: 262
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1402620407

✦ Synopsis

Abstract

To determine the effects of 17β‐estradiol (E~2~) on the properties of the plasma proteins that bind L‐thyroxine (T~4~), immature rainbow trout, Oncorhynchus mykiss, were injected intraperitoneally on days 0 and 3 with 0.5 mg E~2~‐3‐benzoate/100 g body weight, and plasma was sampled on days 4, 7, or 12. Control trout received peanut oil alone. E~2~ caused a small but significant decrease in the free T~4~ index. Saturation analysis on miniature G‐25 Sephadex columns revealed at least two major T~4~‐binding sites. Filtration on agarose Bio‐gel A 1.5 also indicated two major T~4~‐binding protein fractions with molecular weights of 150 and 55 kDa with a small proportion of T~4~ binding to a 1,500‐kDa site presumed to be lipoprotein. Addition of unlabeled T~4~ displaced [^125^I]T~4~ from the 55‐kDa site and unmasked an adjacent site of higher molecular weight. E~2~ increased the proportion of T4 bound to the low‐affinity (150 kDa) site relative to that bound to the high‐affinity (55 KDa site, increased the level of protein associated with the 1,500‐kDa site and its T~4~ binding, and also initiated the production of presumed vitellogenin (VTG), which bound a small amount of T~4~. It is concluded that the E~2~‐induced depression in FT~4~ is caused by a shift in T~4~ binding between high‐affinity and low‐affinity sites, and also by binding of small amounts of T~4~ to presumed lipoprotein and VTG. © 1992 Wiley‐Liss, Inc.