Effects of vertebrate prolactins and growth hormones on thyroxine 5'-monodeiodination in the eel (Anguilla anguilla): a potential bioassay for growth hormone.

Growth hormones (GHs) and prolactins (Prls) purified from representatives of each vertebrate class from bony fish onwards were tested for their ability to stimulate in vivo peripheral deiodination of labeled thyroxine (T4*) into triiodo-L-thyronine (T3*) in the eel. Plasma T3*/T4* ratio was used as parameter. All GHs significantly increased T3*/T4*, the magnitude of the response being unrelated to the phylogenic position of species. No significant stimulation was shown with the various Prl, with the exception of ovine Prl, suggesting a heterosomatotropic effect of this preparation in the eel. Furthermore, both tilapia and ovine GH produced a dose-related effect on plasma T3*, T4*, and T3*/T4*. The stimulation of the peripheral deiodination of T4* into T3* estimated in vivo in the eel could become a specific, sensitive, and rapid fish bioassay for GH.