1) Early enteral feeding could be established in ELBW infants. The critical GRV seems to be above 2 mL/3 mL because there was no significant negative correlation between the mean GRV and V14. 2) Green GR were not negatively correlated with V14 and should not slow down the advancement of feeding volumes in absence of other clinical signs and symptoms.

Objective:The lactulose H 2 -breath test is the most widely used non-invasive approach for evaluation of orocoecal transit time (OCTT). In the present study, doubly-labelled lactose-[ 13 C, 15 N]ureide (DLLU) was synthesized to investigate the OCTT in comparison to the conventional lactulose H 2 -breath test. Additionally, the bacterial breakdown rate (BBR) and rate of elimination and the metabolic pathways of the cleavage products of DLLU ( 13 CO 2 , [ 15 N]urea, and 15 NH 3 ) were investigated. Design and subjects: In a first study, DLLU was administered as a single oral-pulse-labelling (dosage: one gram) either without and after pretreatment of five grams of unlabelled lactoseureide (LU) on the day prior to the study to twelve healthy adult volunteers after breakfast. Breath and urine were collected in one and two hourintervals, respectively, over a one-day period. 13 C-enrichment in breath as well as 15 N-enrichment in urine fractions were measured by continuous flow-isotope ratio mass spectrometry (CF-IRMS). In a second study, lactulose was administered to the same subjects (dosage: ten grams). Breath was collected in quarter, half and one hour-intervals over a ten hour-period. Hydrogen concentration in breath was analysed using an electrochemical detector. Results:The comparison of the lactose-[ 13 C]ureide 13 CO 2 -breath test and the lactulose H 2 -breath test showed that the mean increase of the 13 C-enrichment in CO 2 occurred 1.18 h later than the mean increase of H 2 in breath. The resulting OCTTs derived from the two methods were 3.02 1.7 h (P < 0.01), respectively. The 15 N-enrichment of urinary urea and ammonia without and after pretreatment with LU started between two and three hours after DLLUadministration. The cumulative percentage urinary excretion of the 15 N-and 13 C-tracer was 29.9% and 13.6% respectively, and was slightly increased after LU-pretreatment to 32.1% and 14.6% of the dose administered. A total of 35.2% of the 13 C was found to be exhaled and remained approximately constant after LU-pretreatment (36.2%). Conclusions: The use of the lactulose H 2 -breath test for evaluation of the OCTT showed a statistically significant shortening of 1.18 h in comparison to the lactose-[ 13 C]ureide 13 CO 2 -breath test in healthy adults. The most important limitations of the lactulose H 2 -breath test are its low specificity and sensitivity due to dosedependent accelerations of OCTT, interfering H 2 -rise from malabsorbed dietary fibre and H 2 -non-producers. In contrast, our lactose-[ 13 C]ureide 13 CO 2 -breath test was confirmed to avoid these disadvantages and to yield reliable results. This test is recommended especially if higher sensitivity and specificity is required, if IRMStechnique is available and if lactulose H 2 -tests lead to insufficient results.

The absorption of protein nitrogen by the colon was assessed in 6 infants with colostomy by giving 15N yeast protein in a dosage of 5-20 mg 15N/kg (92.4 atom-% 15N). The absorption of 15N ranged between 87.1 and 98.1% of the administered dose, and the retention in the protein pool ranged between 79.0 and 94.2%. The incorporation of 15N in the plasma proteins was demonstrated by 15N excess values between 0.02 and 0.10 atom-%. The results suggest that the colon can assimilate proteins when insufficient absorption of protein nitrogen in the small intestine occurs. The breakdown of protein is thought to result from the action of colonic flora.

[15N]glycine, [15N]leucine, and [15N]yeast protein thermitase hydrolysate (YPTH) as tracers for investigating the protein turnover rates in premature infants were studied in nine human milk-fed neonates (born after 32 to 34 wk of gestation) by paired comparison of the tracers. The 15N enrichment of total urinary nitrogen and ammonia after administration of a single oral dose of 15N was measured by emission spectrometry. Flux rates were calculated using a three-compartment model and the ammonia end product method. The mean whole-body protein synthesis rates, as determined by the three-compartment model derived from the three 15N tracers, differed significantly (p less than 0.01) among [15N]glycine (15.9 g/kg/d), [15N] leucine (9.1 g/kg/d), and 15N-YPTH (5.9 g/kg/d). When the corresponding rates were determined from the excretion of label in ammonia, the results showed the opposite tendency; the lowest apparent synthesis rates were found after [15N]glycine (7.5 g/kg/d), followed by [15N]leucine (14.4 g/kg/d), and the highest figure resulted after [15N] YPTH (16.7 g/kg/d). The results of this comparison substantiate the assumption that there are methodologic errors in connection with the use of different tracers and models for the calculation of whole-body protein parameters in preterm infants, with respect to the main requirement for tracer kinetic studies; the tracer nitrogen must be representative of total amino acid nitrogen. Seen in this light, mixtures of completely labeled amino acids such as YPTH may represent the most reliable tracer substance.(ABSTRACT TRUNCATED AT 250 WORDS)

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