15N studies of endogenous faecal nitrogen in infants.

(15)N from labelled yeast protein, fed to marasmic and recovered infants, appeared in the stool shortly after administration and continued to be excreted for 100 hours. Unabsorbed dietary (15)N, which appeared with carmine-marked stools, formed only part of this excretion. Calculations of the endogenous nitrogen content of infant stool agreed closely with those of previous workers. The use of intravenously injected (15)N showed that part of the stool nitrogen was derived from this source. It was excreted as urea, ammonia, and other compounds, and totalled about 2% of the administered urea. The persistence of the (15)N in the stool suggests that it had in part been incorporated into cellular material.

Studies with 15N-labeled ammonia and urea in the malnourished child.

Investigations using ammonium citrate-(15)N and urea-(15)N showed that children in the acute stage of kwashiorkor and marasmus receiving a diet of adequate protein content retained a considerable percentage of the label from both compounds. Excretion of both total (15)N and urea-(15)N was subnormal and elimination was virtually completed 36 hr after administration of the isotope. During recovery from kwashiorkor total (15)N excretion had approached normal a month after commencement of rehabilitation. Urea-(15)N excretion was still slightly subnormal after 3 months. In marasmus urea-(15)N formed a normal proportion of total (15)N excretion after 1 month, although total (15)N excretion then was still low. Ammonia nitrogen was retained to a greater extent than urea nitrogen in all cases. As it is known that a considerable amount of urea is degraded to ammonia in the gastrointestinal tract, it seems probable that urea nitrogen became available for use after this degradation. Examination of blood from one marasmic child after feeding ammonia-(15)N and from another after intravenous injection of urea-(15)N showed incorporation of the label into blood cells and plasma proteins. This did not occur in well nourished controls. It is concluded that ammonia and urea as sources of nonessential nitrogen may play an important part in protein metabolism in the malnourished child.