title: Changes in liver concentration of N-acetylglutamate and ornithine are involved in regulating urea synthesis in rats treated with thyroid hormone.
abstract: The purpose of this study was to elucidate the mechanism by which thyroid hormone alters urea synthesis. A set of three experiments was investigated in three groups of rats given 6-propyl-2-thiouracil (a thyroid inhibitor) without triiodothyronine treatment, treated with 6-propyl-2-thiouracil plus triiodothyronine or neither 6-propyl-2-thiouracil nor triiodothyronine (control). We attempted to determine whether the concentration of ornithine and N-acetylglutamate regulated urea synthesis and whether activities of two ornithine-catabolizing enzymes accounted for changes in ornithine concentration. Urinary excretion of urea and the liver concentration of N-acetylglutamate and ornithine in rats given 6-propyl-2-thiouracil plus triiodothyronine were significantly lower than in rats given 6-propyl-2-thiouracil alone. The liver concentration of N-acetylglutamate was correlated to urea excretion (r = 0.911, P less than 0.001). The activities of carbamylphosphate, synthetase, ornithine aminotransferase and ornithine decarboxylase in liver of the group treated with 6-propyl-2-thiouracil alone were significantly lower than those of the 6-propyl-2-thiouracil plus triiodothyronine-treated group. The results suggest that a higher liver concentration of N-acetylglutamate and ornithine in the hypothyroid (6-propyl-2-thiouracil only) rats is likely to stimulate urea synthesis. The thyroid hormone-induced increase in activities of ornithine catabolizing enzymes may be primarily responsible for changes in ornithine concentration.
authors.affiliation: Department of Home Economics, Aichi University of Education, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hayase
authors.forename: G
authors.initials: G
authors.lastname: Yonekawa
authors.forename: A
authors.initials: A
authors.lastname: Yoshida
mesh_terms: D000818:Animals; D001835:Body Weight; D005971:Glutamates / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D009929:Organ Size; D009952:Ornithine / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000378:metabolism; D009953:Ornithine-Oxo-Acid Transaminase / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000494:pharmacology*; D014508:Urea / Q000097:blood / Q000378:metabolism*
chemical_list: D005971:Glutamates; D013963:Thyroid Hormones; D014508:Urea; D009952:Ornithine; D009953:Ornithine-Oxo-Acid Transaminase; D009955:Ornithine Decarboxylase; C016195:N-acetylglutamic acid