Somatostatin increases plasma T3 concentrations in Tilapia nilotica in the presence of increased plasma T4 levels.
An injection of ovine growth hormone, porcine follicle stimulating hormone, and bovine thyrotropin stimulating hormone increased in Tilapia nilotica plasma concentrations of thyroxine (T4) and reverse triiodothyronine (rT3) after 4 and 8 hr, whereas plasma concentrations of T3 were unaffected. An injection of somatostatin (SRIF) alone did not influence thyroid hormone levels. If, however, SRIF was injected together with these hormones, which raised plasma T4, or together with T4 itself, an increase in plasma concentrations of T3 could be observed, whereas the increase in rT3 was less pronounced. It is concluded that SRIF may change the normal 5-deiodinase (5-D) activity and increased rT3 during hyperthyroxinemia into a 5'-D activity and a rise in T3, respectively, in T. nilotica.
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Laboratory of Comparative Endocrinology, Catholic University of Leuven, Belgium.
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Kühn
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D000818:Animals; D005399:Fishes / Q000097:blood*; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D013006:Growth Hormone / Q000494:pharmacology; D007700:Kinetics; D013004:Somatostatin / Q000494:pharmacology*; D013972:Thyrotropin / Q000494:pharmacology; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D014285:Triiodothyronine, Reverse / Q000097:blood
D014284:Triiodothyronine; D013004:Somatostatin; D014285:Triiodothyronine, Reverse; D005640:Follicle Stimulating Hormone; D013972:Thyrotropin; D013006:Growth Hormone; D013974:Thyroxine