Glutamate interconversions and glucogenicity in the sheep

Area of Science:

• Metabolic Physiology
• Animal Nutrition
• Biochemistry

Background:

• Glutamate is a crucial amino acid involved in various metabolic pathways.
• Understanding glutamate metabolism is vital for animal health and physiological regulation.

Purpose of the Study:

• To quantify net and unidirectional glutamate metabolism in different ovine tissues.
• To assess the contribution of glutamate to glutamine and glucose production under varying physiological states.
• To investigate the impact of acidosis and fasting on glutamate flux and interconversion.

Main Methods:

• Simultaneous measurement of net and unidirectional glutamate flux in portal-drained viscera, liver, kidneys, and hindquarters of sheep.
• Utilized radiolabeled [14C]glutamate to trace metabolic pathways.
• Compared glutamate metabolism in fed, acidotic, and fasted states.

Main Results:

• Blood glutamate concentrations decreased with acidosis and fasting.
• Liver was a major source of plasma glutamate in fed sheep, while hindquarters utilized it; both fluxes were reduced by nutritional and acid-base challenges.
• Acidosis and fasting predominantly affected hepatic glutamate production and hindquarter utilization.
• Glutamate conversion to glutamine was low (12-25%), with most occurring extrarenally.
• Glutamate contributed significantly to glucose production (20-26%), with kidneys playing a key gluconeogenic role, especially during acidosis and fasting (40-45%).

Conclusions:

• Glutamate metabolism is significantly altered by acidosis and fasting in sheep.
• The liver and hindquarters show altered glutamate flux in response to physiological stress.
• Kidneys play a substantial gluconeogenic role, particularly under conditions of acidosis and fasting.