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Articles in PresS, published online ahead of print November 5, 2001
Am J Physiol Endocrinol Metab, 10.1152/ajpendo.00403.2001
Submitted on September 11, 2001
Accepted on October 31, 2001
1 Robert Schwartz M.D. Center for Metabolism & Nutrition, MetroHealth Medical Center, Cleveland, OH, USA; Pediatrics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
2 Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH, USA; Robert Schwartz M.D. Center for Metabolism & Nutrition, MetroHealth Medical Center, Cleveland, OH, USA; Pediatrics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
* To whom correspondence should be addressed. E-mail: sck{at}po.cwru.edu.
Glutamine kinetics and its relation to transamination of leucine and urea synthesis were quantified in 16 appropriate for gestational age, four small for gestational age and seven infants of diabetic mothers in the immediate neonatal period. Kinetics were measured between 4-5 hours after the last feed (fasting) and in response to formula feeding. [5-15N]glutamine, [1-13C15N]leucine, [2H5]phenylalanine and [15N2]urea tracer were administered as prime constant rate infusion, and the rates of appearance were quantified using steady state kinetics. Leucine nitrogen and glutamine kinetics during fasting were significantly higher than those reported in adults. De novo synthesis accounted for ~85% of glutamine turnover. In response to formula feeding, a significant increase (p = 0.04) in leucine nitrogen turnover was observed while a significant decrease (p = 0.002) in glutamine and urea rate of appearance was seen. The rate of appearance of leucine nitrogen was positively correlated (r2 = 0.59, p = 0.001) with glutamine turnover. Glutamine flux was negatively correlated (r2 = 0.39, p = 0.02) with the rate of urea synthesis. A significant negative correlation was observed between body weight and whole body proteolysis measured by rate of appearance of phenylalanine (r2 = 0.42, p = 0.008). These data suggest that in the human newborn, glutamine turnover is related to a high anaplerotic flux into the TCA cycle as a consequence of a high rate of protein turnover. The negative relationship between glutamine turnover and the irreversible oxidation of protein (urea synthesis) suggest an important role of glutamine as a nitrogen source for other synthetic processes and accretion of body proteins.
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