Hayase K, Yonekawa G, Yoshida A
Department of Home Economics, Aichi University of Education, Japan.
J Nutr. 1992 May;122(5):1143-8. doi: 10.1093/jn/122.5.1143.
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.
本研究的目的是阐明甲状腺激素改变尿素合成的机制。在三组大鼠中进行了一组三个实验，这三组大鼠分别给予6-丙基-2-硫氧嘧啶（一种甲状腺抑制剂）且未用三碘甲状腺原氨酸治疗、给予6-丙基-2-硫氧嘧啶加三碘甲状腺原氨酸治疗或既未给予6-丙基-2-硫氧嘧啶也未给予三碘甲状腺原氨酸（对照组）。我们试图确定鸟氨酸和N-乙酰谷氨酸的浓度是否调节尿素合成，以及两种鸟氨酸分解代谢酶的活性是否解释了鸟氨酸浓度的变化。给予6-丙基-2-硫氧嘧啶加三碘甲状腺原氨酸的大鼠的尿素尿排泄量以及肝脏中N-乙酰谷氨酸和鸟氨酸的浓度显著低于仅给予6-丙基-2-硫氧嘧啶的大鼠。肝脏中N-乙酰谷氨酸的浓度与尿素排泄相关（r = 0.911，P小于0.001）。仅给予6-丙基-2-硫氧嘧啶治疗组大鼠肝脏中的氨基甲酰磷酸合成酶、鸟氨酸氨基转移酶和鸟氨酸脱羧酶的活性显著低于给予6-丙基-2-硫氧嘧啶加三碘甲状腺原氨酸治疗组。结果表明，甲状腺功能减退（仅给予6-丙基-2-硫氧嘧啶）大鼠肝脏中较高浓度的N-乙酰谷氨酸和鸟氨酸可能会刺激尿素合成。甲状腺激素诱导的鸟氨酸分解代谢酶活性增加可能是鸟氨酸浓度变化的主要原因。
