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Gluconeogenesis from Amino Acids in Mature Wether Sheep¹

University of Maine, Orono, Maine 04473

Three mature wether sheep fed at maintenance levels and equipped with indwelling jugular catheters were infused with glutamate-U-¹⁴C, glucose-U-¹⁴C, and serine-U-¹⁴C for periods of 6 hours with interim periods of 3 and 8 hours following the first and second infusions, respectively. There exists the possibility of some residual effects due to the sequential infusion of the three different metabolites. The specific activities of expired CO₂, plasma glucose, and plasma amino acids over the last 3 hours of infusion were determined and the individual oxidation, turnover, and production rates were calculated. The turnover rates for glutamate, glucose, and serine were 0.596, 1.262, and 0.222 mg/minute/kg, respectively. The percentage of glutamate, glucose, and serine metabolized to CO₂ was 57.7, 31.8, and 24.2, respectively. The percentage of CO₂ originating from glutamate, glucose, and serine was 5.3, 5.8, and 0.7, respectively. The percentage of serine metabolized to glucose was 10.7 while 1.7% of the plasma glucose originated from serine. The percentage of glutamate metabolized to glucose was 11.3 while 6.2% of the plasma glucose originated from glutamate. Although no activity was found in the plasma glutamate fraction during glucose infusion, activity was found in the plasma serine and alanine fractions. A total of 8% of the plasma glucose originated from the two amino acids studied. In addition, 6% of the expired CO₂ resulted directly from the oxidation of these two amino acids. It would appear that amino acids are not only an important source of glucose in the ruminant, but serve as a direct source of energy as well.

KEY WORDS: • gluconeogenesis • amino acids • ruminant • plasma glucose

¹ Supported in part by a grant from Agway, Syracuse, N. Y.

Manuscript received 18 May 1973.