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Arginine Affects Urea Synthesis in Rats Treated with Thyroid Hormone

Department of Home Economics, Aichi University of Education, Kariya, Aichi 448, Japan ^* Department of Agricultural Chemistry, Nagoya University, Chikusa, Nagoya 464-01, Japan

The purpose of the present study was to determine whether the regulation of urea synthesis was mediated through the activation of N-acetylglutamate synthesis by arginine and whether the concentration of glutamate or activity of N-acetylglutamate synthetase might control N-acetylglutamate concentration when the thyroid status was manipulated. Three groups of rats were given 6-propyl-2-thiouracil (PTU, thyroid inhibitor) without triiodothyronine (T₃) treatment, treated with PTU + T₃ or treated with neither PTU nor T₃ (control). Urinary excretion of urea, liver concentration of N-acetylglutamate and plasma concentration of arginine in rats given PTU + T₃ were significantly lower than in rats given PTU alone. Liver concentration of N-acetylglutamate was correlated with plasma concentration of arginine (r = 0.842, P < 0.001). The activity of N-acetylglutamate synthetase and glutamate concentration in liver of the PTU + T₃-treated group were significantly higher than in the group treated with PTU alone. Arginine administration (0.5 mmol/100 g body wt) elevated the liver concentration of N-acetylglutamate in all three groups. The results suggest that the greater concentration of arginine in the hypothyroid (PTU alone) rats is likely to increase the N-acetylglutamate concentration and stimulate urea synthesis.

KEY WORDS: • triiodothyronine • urea synthesis • N-acetylglutamate • arginine • rats

¹ To whom correspondence should be addressed.

Manuscript received 15 July 1992. Revision accepted 16 October 1992.