Determination of 3,5,3′-triiodo-L-thyronine (T3) levels in tissues of rainbow trout (Salmo gairdneri) and the effect of low ambient pH and aluminum

Abstract

Tissue T3 (3,5,3'-triiodo-L-thyronine) concentrations were measured in rainbow trout, Salmo gairdneri, after digestion by Pronase or collagenase and extraction with ethanolic ammonia (99:1, v/v) followed by 2N NH4OH and chloroform. Recoveries of [(125)I]T3 administered in vivo or in vitro were high and consistent and there was close parallelism between sample dilutions and the radioimmunoassay curve, but recoveries of unlabeled T3 administered in vitro were low and variable. Alternatively, trout were brought to isotopic equilibrium by [(125)I]T3 infusion for 96 h, the extracted [(125)I]T3 determined by gel filtration and the tissue T3 content calculated from the specific activity of plasma [(125)I]T3. By the latter method, tissue T3 concentrations were: intestine (4.2 ng/g), kidney (2.5), liver (2.8), stomach (1.5), heart (1.0), muscle (0.7), gill (0.6) and skin (0.3). Muscle (67% of body weight) comprised the largest tissue T3 pool (82% of all tissues examined). Seven days exposure of trout to water acidified with H2SO4 (pH 4.8) or acidified water containing aluminum (21.6 mM), decreased tissue T3 content generally and particularly in muscle (14% of controls). In conclusion, skeletal muscle is the largest T3 tissue pool and seems highly responsive to altered physiologic state.

Measurement and regulation of thyroidal status in teleost fish

“…However, in contrast to mammals, where plasma T4 exceeds plasma T 3 by 50-100:1, the plasma T 3 level in teleosts may exceed that of T4. Thus, the T 3 measured in the blood and tissues (Fok et al, 1990;Specker et al, 1992) is probably derived extrathyroidally from T4 by removal of a single outer-ring iodine by 5'-monodeioidinase (T4ORD) activity (Fig. 6) (Leathefland, 1981;Pimlott and Eales, 1983;Shields and Eales, 1986).…”

“…Following removal of contaminating lipids with chloroform, the T 3 concentration from subsequent alcohol extracts can be measured by immunoassay with allowance for T 3 recovery (Tagawa and Hirano, 1990). Alternatively, fish may be brought to isotopic equilibrium through constant *T a infusion, tissues homogenized, lipid removed, alcohol extracts prepared, *T 3 identified chromatographically, and absolute T 3 levels calculated from the specific activity of the *T3 based on plasma measurements (Fok et al, 1990). Such approaches have been employed to assess tissue T 3 levels of adult trout (Fok et al, 1990) or immature coho salmon during parr-smolt transformation (Specker et al, 1992), and in the whole eggs, yolk, larvae and fry of salmonids (Greenblatt et al, 1989;Leatherland et al, 1989;Tagawa and Hirano, 1990;deJesus and Hirano, 1992), flounder (Tagawa et al, …”

“…Furthermore, the tissue T3/T 4 ratio can vary over a wide range, indicating that at both the tissue and plasma levels there is asynchronous regulation of T 3 and T4. These discrepancies occur during parr-smolt transformation (Specker et al, 1992), and exposure to sublethal low pH/high AI3 + levels (Fok et al, 1990). How does one interpret tissue T 3 concentrations?…”

“…The concept of two T3 compartments in lake trout liver was suggested by Weirich et al (1987). Muscle, on the other hand, contains a low T3 level, but owing to its large mass comprises a total tissue pool representing about 80% of all the T 3 in the rainbow trout (Fok et aL, 1990). It may represent a source of T 3 which exchanges slowly with plasma.…”

Environmental factors affecting thyroid function of wild sea bass (Dicentrarchus labrax) from European coasts

“…The concentrations vary between the different species, but they do support the roles of thyroid hormones in early development and during metamorphosis. Muscle contains low amounts of T 3 , but owing to its large mass comprises a total tissue pool representing about 80% of all the T 3 in the rainbow trout (Fok et al, 1990). The muscular thyroid hormone concentrations should thus provide a good index of the thyroid hormone reserves in fish.…”