Effects of L-thyroxine and L-triiodothyronine on protein and nucleic acid contents of liver of 6N-2-propylthiouracil treated hypothyroid singi fish, Heteropneustes fossilis bloch.
Three consecutive injections of 12.5 X 10(-10) and 25 X 10(-10) moles/g of L-thyroxine (T4) or a single injection of L-triiodothyronine (T3) at 7.5 X 10(-10) moles/g to Singi fish caused an increase in liver protein and RNA contents, whereas similar injections of 50 X 10(-10) moles/g of T4 or 75 X 10(-10) moles/g of T3 caused a fall in these cellular constituents in liver. Treatments of Singi fish with thiourea (1 mg/ml) for 30 days caused a fall in the protein and RNA contents in liver which were restored to the euthyroid control level by a single injection of 7.5 X 10(-10) moles/g of T3 or three consecutive injections of T4 at 12.5 X 10(-10) moles/g dose. Administration of T4 (12.5 X 10(-10) moles/g, three consecutive injections) along with 6N-2-propylthiouracil (PTU) at 20 micrograms/g of b. w. in six consecutive injections to the thiourea treated (hypothyroid) fish failed to cause any change in hepatic protein and RNA contents in comparison to only PTU-treated hypothyroid fish, but a single injection of 7.5 X 10(-10) moles/g of T3 to the PTU-treated hypothyroid fish increased these cellular constituents of liver. A dose-dependent biphasic nature of thyroid hormone action, a higher potency of T3 than T4 and the probable 'prohormone' nature of T4 have been documented in case of Singi fish in the present experiments.
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Department of Animal Physiology, Bose Institute, Calcutta, India.
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D000818:Animals; D004247:DNA / Q000378:metabolism; D005399:Fishes / Q000378:metabolism*; D007037:Hypothyroidism / Q000139:chemically induced / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009696:Nucleic Acids / Q000378:metabolism*; D011441:Propylthiouracil / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
D009696:Nucleic Acids; D011506:Proteins; D014284:Triiodothyronine; D012313:RNA; D011441:Propylthiouracil; D004247:DNA; D013974:Thyroxine