Negative feedback regulation of thyrotropin subunits and pituitary deiodinases in red drum, Sciaenops ocellatus.
Thyroxine (T4) undergoes dynamic daily cycles in the perciform fish the red drum, Sciaenops ocellatus, that are inversely timed to cycles of thyrotropin (TSH) subunit mRNA expression in the pituitary gland. We have proposed that these daily cycles are regulated by negative feedback of circulating T4on expression of pituitary thyroid hormone deiodinase type 3 (Dio3), such that elevated circulating T4results in diminished pituitary thyroid hormone catabolism and consequent increased negative feedback on expression of TSH subunits during the day. To determine whether thyroid hormones function to modulate expression of pituitary deiodinase enzymes we developed an immersion technique to administer physiological doses of T3and T4in vivo. Immersion in T4or T3significantly inhibited the mRNA expression of the TSH α and β subunits from 4 to 66h of immersion. Pituitary Dio3 expression was significantly diminished by T3and T4at 22h. These results indicate that both T4and T3are capable of negative feedback regulation of TSH subunit expression in red drum at physiological concentrations and on a time scale consistent with the T4daily cycle. Furthermore, thyroid hormones negatively regulate Dio3 expression in the pituitary in a manner suggesting that negative thyroxine feedback on Dio3 promotes the release of TSH subunits from TH inhibition and may be an important mechanism for generating daily thyroid hormone cycles. These results highlight a potentially important role for D3 in mediating thyroid hormone feedback on TSH expression, not previously described in other species.
Department of Biology, Texas A&M University, 3258 TAMUS, College Station, TX 77843-3258, USA. Electronic address: rajones@bio.tamu.edu.
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Jones
Department of Biology, Texas A&M University, 3258 TAMUS, College Station, TX 77843-3258, USA. Electronic address: bcohn@bio.tamu.edu.
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Cohn
Department of Biology, Texas A&M University, 3258 TAMUS, College Station, TX 77843-3258, USA. Electronic address: awilkes@bio.tamu.edu.
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Wilkes
Department of Biology, Texas A&M University, 3258 TAMUS, College Station, TX 77843-3258, USA. Electronic address: duncan@bio.tamu.edu.
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MacKenzie
D000818:Animals; D005399:Fishes; D007453:Iodide Peroxidase / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism*; D013961:Thyroid Gland / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism*
D013963:Thyroid Hormones; D013972:Thyrotropin; C117274:iodothyronine deiodinase type III; D007453:Iodide Peroxidase; D013974:Thyroxine
Deiodinase; Fish; Negative feedback; Thyroid hormone; Thyrotropin