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Dietary Threonine Imbalance Alters Threonine Dehydrogenase Activity in Isolated Hepatic Mitochondria of Chicks and Rats^1,2,

Department of Animal Science, Cornell University, Ithaca, NY 14853

Experiments were conducted on chicks and rats to determine whether hepatic threonine dehydrogenase activity is modified by the consumption of a threonine-imbalanced diet and to determine the tissue distribution of this enzyme. Threonine imbalances were created by supplementing basal diets with branchedchain amino acids (6 g/100 g diet for chicks) or a mixture of indispensable amino acids (5.6 g/100 g diet for chicks and 5.4 g/100 g diet for rats). Chicks fed threonine-imbalanced diets consistently had twice the hepatic threonine dehydrogenase activity of those fed the basal diet when measured in one experiment at 24 h and in two experiments at 216 h (P < 0.05). Rats received the experimental diets for 12 or 24 h in one experiment and for 12, 24, 72 or 168 h in another experiment. In the first experiment, rats fed the threonine-imbalanced diet had significantly greater hepatic threonine dehydrogenase activity (P < 0.05) at 12 h but not at 24 h. In the other rat experiment, threonine dehydrogenase activity in the rats fed the threonine-imbalanced diet was significantly greater than in controls at 72 h, but tended to be lower at 168 h, which coincided with the adaptation of the rats to the imbalanced diet. Threonine dehydrogenase activity was widespread in tissues of both species. The results indicate that alterations in hepatic threonine dehydrogenase activity occur in chicks and rats subjected to threonine imbalance.

KEY WORDS: • threonine dehydrogenase • imbalance • tissues • rats • chicks

¹ Presented in part at Experimental Biology 93, March 1993, New Orleans, LA [Davis, A. J. & Austic, R. E. (1993) Increased hepatic threonine dehydrogenase (TDH) activity in chicks and rats subjected to dietary threonine (THR) imbalance. FASEB J. 7: A392 (abs.)].

² Supported in part through Hatch project no. 157405 and by a generous gift from BioKyowa, Inc., Chesterfield, MO.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence and reprint requests should be addressed.

Manuscript received 12 November 1993. Revision accepted 8 March 1994.

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