Whole-body Protein Breakdown and 3-Methylhistidine Excretion During Brief Fasting, Starvation, and Intravenous Repletion in Man

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Abstract
Simultaneous whole-body protein breakdown (using 15N-glycine) and urinary 3-methylhistidine (3MH) excretion rates were determined in 6 hospitalized normal volunteers after 10 days of starvation and a subsequent 10-day period of total parental nutrition (TPN). These data were contrasted to whole-body protein breakdown and urinary 3MH excretion in 10 depleted (14.8% body weight loss) patients with benign intraabdominal disease studied in the basal (48 h without nutrient intake) and i.v. refed states. The rates of whole-body protein breakdown were significantly reduced from basal (brief fasting or starvation) conditions in both normal volunteers (P < 0.01) and depleted patients (P < 0.01) during TPN. The rate of protein catabolism normalized for creatinine excretion in patients was higher than that observed in normal subjects during both basal (P < 0.05) and i.v. feeding conditions. Daily urinary 3MH excretion was reduced during i.v. feeding in both starved normal volunteer (235 .+-. 13 .mu.mol/d to 197 .+-. 9 .mu.mol/d P < 0.05) and in depleted patients (209 .+-. 31 .mu.mol/d to 140 .+-. 35 .mu.mol/d), and an apparent linear relationship between protein breakdown and urinary 3MH, normalized for creatinine excretion, was obtained in both volunteer and patient (r = 0.85) populations during fasting-refeeding. However, separate regression analysis of the protein breakdown and 3MH responses of both volunteer and patient groups under conditions of fasting, starvation, and refeeding revealed significant differences between volunteer and patient populations during i.v. refeeding (P < 0.01). Further analysis of 3MH excretion in relationship to nitrogen balance during refeeding suggests a complex relationship between urinary 3MH excretion and whole-body protein metabolism that may be partly related to the degree of antecedent malnutrition.