title: Comparative study on the effects of thyroxine on protein, RNA and DNA contents of liver of different vertebrates at different stages of life.
abstract: The relative responsiveness of different vertebrates (mammals, amphibia, and fish) at different stages of life to thyroxine (T4) with respect to protein and nucleic acids contents of liver has been studied. The control growing rat, toad, and Lata fish showed a gradual rise in the protein content of liver with the advancement of age. The rat liver RNA reached a maximum level at the 15th d (immature stage) of life and this level was maintained in 30 (juvenile) and 60th d (adult) of life. In the toad, no significant difference in liver RNA was observed with age. Fish liver, however, showed more RNA in juvenile stage than that in immature stage; no such difference was observed in between juvenile and adult stages of life. In normal growing rat, the liver DNA was found to be reduced in juvenile stage from that of immature stage. But in adult stage, the level of DNA was more or less at the same level as that of immature stage of the animals. Fish liver DNA did not exhibit any change with age. But in the toad, the progress of the stages of life was associated with the enhancement of liver DNA. Administration of T4 for 5 consecutive d caused an increase in protein, RNA and DNA contents of liver of rat, toad and Lata fish of different age groups excepting liver DNA in adult toad and fish. The dose of 1 microgram of T4 per g produced maximum effects in these animals. The T4-induced percentage increase in the amount of liver DNA was maximum in immature stage of life; this was followed by an increase in RNA and then by protein. In juvenile stage of these animals, RNA shows maximum increase followed by DNA and/or protein; and in adult stage, the rate of percentage increase in liver RNA was maximum followed by protein and DNA. The dose-response relationship between rat, toad, and Lata fish after T4 treatment (1 microgram/g) revealed that the poikilothermic vertebrates (toad and Lata fish) were more responsive than homoiotherm (rat) so far as the T4-induced increase in liver protein, RNA, and DNA are concerned.
mesh_terms: D000367:Age Factors; D000818:Animals; D002025:Bufonidae; D004247:DNA / Q000032:analysis*; D005399:Fishes; D008099:Liver / Q000032:analysis / Q000187:drug effects*; D008297:Male; D011506:Proteins / Q000032:analysis*; D012313:RNA / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000494:pharmacology*; D014714:Vertebrates
chemical_list: D011506:Proteins; D012313:RNA; D004247:DNA; D013974:Thyroxine