Tracer priming in human protein turnover studies with [15N]glycine.
Sixty-three studies in healthy normal volunteers (n = 29), malnourished cancer (n = 8) or non-cancer patients (n = 9), and postoperative radical cystectomy patients (n = 17) were conducted to evaluate the primed constant infusion labeling technique for the estimation of whole-body protein turnover under a variety of dietary conditions. [15N]Glycine was used as the tracer with a prime to infusion ratio of 1300 to 3300 min and a continuous-infusion rate of 0.11 to 0.33 micrograms 15N . kg-1 . min-1 for 24 to 36 hr. The isotopic steady-state enrichment was reached in all subjects both in urinary urea and ammonia between 10 and 26 hr (mean 18 +/- 2). During protein calorie fasting the attainment of isotopic steady state is much quicker (10 to 18 hr) with a primed constant infusion than with a constant infusion alone (approximately 38 hr). A P/I ratio greater or less than 1800 (min) usually resulted in a delay of plateau attainment without affecting the protein turnover values. Reliable estimates of protein kinetics in humans can be made in clinical conditions with a 26-hr infusion of glycine at the rate of 0.28 microgram 15N . kg-1 . min-1 with a P/I ratio of 1800 min, collecting six urine samples every 2 hr from 16 hr and analyzing for both urinary urea and ammonia enrichments.
D000641:Ammonia / Q000652:urine; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007263:Infusions, Parenteral; D007275:Injections, Intravenous; D007700:Kinetics; D008433:Mathematics; D008657:Metabolic Clearance Rate; D009369:Neoplasms / Q000378:metabolism; D009584:Nitrogen / Q000652:urine; D009587:Nitrogen Isotopes; D009748:Nutrition Disorders / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*
D009587:Nitrogen Isotopes; D011506:Proteins; D000641:Ammonia; D009584:Nitrogen; D005998:Glycine