Muscle Protein Degradation in Premature Human Infants

Abstract

1. Myofibrillar protein degradation has been measured by the rate of 3-methylhistidine excretion in premature infants weighing between 635 g and 1295 g. Analyses were made in conjunction with 1--3 day nitrogen balance studies. 2. In 56 balance studies in 36 infants, total muscle protein breakdown varied between 0.70 and 2.58 (mean 1.05) g day-1 kg-1 body weight while the percentage of total muscle protein degraded each day was between 3.3 and 8.3 (mean 4.8). 3. Both total and fractional rates of protein breakdown showed highly significant negative correlations with nitrogen retention but no relationship to total energy input. 4. Protein degradation was higher than average in infants who were losing weight at the time of the balance study, lower in infants who were gaining weight and higher in those who died within 2 weeks of the analysis. 5. Myofibrillar protein breakdown was not different between infants fed orally and those receiving total parenteral nutrition. 6. Generally the effects of nitrogen and evergy status on muscle protein degradation in the premature infants are different from changes reported in adult human beings or adult rats. We suggest that this difference may be a consequence of the very limited energy reserves of the premature infant.

3-Methylhistidine/Creatinine Ratio in Urine from Low-Birth-Weight Infants

“…In comparison to the results of Seashore et al [8] in a group of 17 preterm infants (16.8 ± 4.4 pmol/mmol) we found somewhat higher values. Ballard et al [6] found a mean 3-methylhistidine/creatinine ratio of 43.8 pmol/mmol in 23 preterm in fants who had a birth weight of about 0.9 kg and were gaining weight at the time of the study. This extremely high value can be ex plained by the unusually low creatinine val ues determined by these authors in studies with subjects of different ages, which were in the range of 50% of the creatinine values described by us and others [8,9], Pencharz et al [16] found a mean 3-methylhistidine/cre atinine ratio of 29 pmol/mmol (range in the mean value of different groups of preterm infants: 20.4-54 pmol/mmol) which they re garded as normative.…”

“…Therefore in this group insufficient energy and protein supply can easily result in protein catabolism. In addi tion stress, like infections, which frequently occurs in low-birth-weight infants, is known to cause increased protein breakdown often accompanied by a concomitant increase in protein synthesis [5], For these reasons it has been proposed to use 3-methylhistidine ex cretion in 24-hour urine as a tool to judge nutritional and metabolic state of preterm infants [6][7][8].…”

3-Methylhistidine as a Measure of Skeletal Muscle Protein Breakdown in Human Subjects: The Case for Its Continued Use

“…Two situations where the 3-MeH method has been applied and which may fit the above pattern are premature infants and Duchenne muscular dystrophy. Estimates of muscle mass calculated from creatinine excretion rates in 1000 g premature infants indicated that an average of only 11% of the body weight was muscle [32]. Since the 3-MeH excretion rate per kg of body weight in these infants was similar to that of adult subjects, provided allowance is made for the somewhat lower 3-MeH content of infant muscle, the rate of muscle-protein breakdown rate calculated from the 3-MeH/creatinine ratio was about fourfold higher in the infants.…”

Hormonal and Metabolic Response to Operative Stress in the Neonate

“…,213 The previous study 166 failed to demonstrate any correlation between energy input in the premature infant and the rate of muscle protein breakdown, in contrast to the findings of Zlotkin 177 and Duffy and Pencharz. 176 Ballard et al felt this may be due in part to the size of the fat reserves, since there is evidence that ketonemia produced by fat mobilization is accompanied by a lower rate of muscle protein breakdown 166. However, they pointed out that the preterm human neonate has relatively little adipose tissue and may be expected to demonstrate increased muscle protein catabolism when energy intake is minimal.…”