442 URINARY 3-METHYLHISTIDINE EXCRETION IN NORMAL AND STRESSED INFANTS

The unusual amino acid 3-methylhistidine (3MH) is present only in muscle (the major protein mass in the body). Urinary 3MH is an ideal indicator of protein catabolism because the one mole of 3MH released upon breakdown of each mole of actin and myosin heavy chain is excreted from the body without reutilization. We are presently investigating the effects of parenteral nutrition on the protein metabolic state of neonates whose oral nutrient intake for various clinical conditions is inadequate. In a preliminary study 17 3MH/creatinine ratio measurements were performed on spot urines in 6 premature and 5 term infants. The newborns who were healthy and growing were found to have a ratio of 0.222± 0.016 (mean and S.D.) which value is about two times higher than that of normal adults in our population. The 3MH/creatinine ratio was significantly elevated (range 0.270 - 0.690; mean 0.377 ± 143 S.D.) in infants who were losing weight and had low nutrient intake because of prematurity, sepsis or postoperative condition. The relatively high 3MH/creatinine ratio in normal growing infants is consistent with the elevated metabolic rate and protein turn-over in neonates. The rise in the ratios of stressed infants reflects increased muscle protein catabolism which is apparently secondary to malnutrition. (Supported by HD-10235)