INFLUENCE OF TESTOSTERONE PROPIONATE ON THYROID-FUNCTION OF IMMATURE RAINBOW-TROUT, SALMO-GAIRDNERI RICHARDSON

Testosterone propionate (TP) was injected intramuscularly (five injections at 4-day intervals) into fed immature rainbow trout at 11-12°; controls were sham injected. TP increased thyroxine (T4) degradation rate, T4 deiodination rate, T4 conversion to 3,5,3′-triiodo-l-thyronine (T3), plasma T3 levels, and thyroid uptake of radioiodide 48-96 hr after radioiodide injection. However, plasma T4 levels responded inconsistently to TP, while thyroid radioiodide uptake measured earlier than 24 hr was suppressed by TP. In conclusion, (i) TP, either directly or indirectly, stimulates many aspects of thyroid function, including conversion of T4 to T3, and (ii) plasma T4 level and thyroidal uptake of radioiodide can be highly misleading indexes of thyroid function. © 1979.