1. Glutamine [15N]amide was infused at a steady rate of 33.34 μmol/h into seven male adult volunteers who were in the fed state and normal acid-base status.
2. Plasma glutamine amide N enrichment and urinary ammonia N enrichment rose to a constant value within 3 h.
3. The glutamine production rate was 51.8 ± 7.9 mmol/h.
4. The total ammonia excretion rate was 0.87 mmol/h. Of this excreted ammonia 62.6 ± 9% was derived from the amide N atom of glutamine.
5. The excreted glutamine amide N (0.53 mmol/h) was only 1% of the glutamine production. If half the ammonia formed by the kidney is excreted in urine and half liberated into the renal vein in subjects with normal acid-base status [E. E. Owen & R. R. Robinson (1963) Journal of Clinical Investigation, 42, 263–276], then the kidney accounts for only 2% of glutamine disposal.
6. Whole body protein turnover, measured from the urinary [15N]ammonia enrichment, was 30.3 ± 7.7 g of N/day (2.8 g of protein day−1 kg−1).