Effects of tuberculosis and HIV infection on whole-body protein metabolism during feeding, measured by the [15N]glycine method.

BACKGROUND: Tuberculosis (TB) and HIV infection are wasting diseases that frequently occur together and have severe consequences on nutritional status. OBJECTIVE: The objective was to determine the effects of TB and HIV, separately and together, on protein metabolism. DESIGN: Protein metabolism was determined in the fed state in 11 healthy control subjects, in 10 patients with HIV infection without TB or other active infection (HIV group), in 10 patients with active TB without HIV infection (TB group), and in 8 patients with HIV infection and active TB (HIVTB group) with the use of oral [(15)N]glycine and measurement of enrichment in urinary urea and ammonia. RESULTS: Whole-body protein flux and degradation were lower in the HIV group than in the control group (mean flux: 3.53 +/- 0.40 compared with 4.75 +/- 0.97 g. kg lean body mass(-1). 12 h(-1); P = 0.002). Protein flux, synthesis, and degradation were not significantly different between the control group and the TB and HIVTB groups. Net protein balance was strongly anabolic in the control, HIV, and TB groups but was neutral in the HIVTB group (P < 0.001 for comparison between groups). CONCLUSIONS: HIV infection was associated with a significant down-regulation of whole-body protein flux. TB alone was not associated with abnormal protein metabolism, but net anabolism in the fed state was impaired in the HIVTB group.

Urinary 5-L-oxoproline (pyroglutamic acid) excretion is greater in infants in Jamaican than in infants in England

OBJECTIVE: To determine the pattern of excretion in urine of 5-L-oxoproline, as a measure of glycine status, during the first six weeks of life in Jamaican infants. DESIGN: Spot samples of urine were collected from term and preterm infants at birth and longitudinally to four weeks of age, or at six weeks of age. 5-L-oxoproline was isolated by column chromatography and hydrolysed to L-glutamic acid, which was measured enzymatically and results expressed relative to creatinine excretion. SETTING: Maternity wards and postnatal clinic of the University Hospital of the West Indies. SUBJECTS: African-Caribbean infants, 19 term and 21 preterm, from birth to four weeks of age, and 79 term infants at six weeks of age. RESULTS: There was no difference between term and preterm infants. Excretion of 5-L-oxoproline increased progressively from birth, 141 æmol/mmol creatinine at four weeks of age. At six weeks of age, excretion was significantly greater than at birth or four weeks of age, 525 æmol/mmol creatinine. Compared with infant born in England, the excretion of 5-L-oxoproline was not different at birth, but was significantly greater in Jamaican infant at six weeks of age. CONCLUSIONS: Glycine status, indicated by increased excretion of 5-L-oxoproline, is marginal in Jamaican infants at six weeks of age, and this is possibly reflects a limitation in the endogenous biosynthesis of glycine due to a dietary limitation of folate or vitamin B-12. (AU)

Urea kinetics in healthy women during normal pregnancy

Urea kinetics were measured in normal women aged 22-34 years at weeks 16, 24 and 32 on either their habitual protein intake (HABIT) or a controlled intake of 60 g protein/d (CONTROL), using primed-intermittent oral doses of [15N15N] urea and measurement of plateau enrichment in urinary urea over 18 h (ID) or a single oral dose of [15N15N] urea and measurement of enrichment of urea in urine over the following 48 h (SD). The intake of protein during HABIT-ID (80 g/d) was greater than that on HABIT-SD (71 g/d); urea production as a percentage of intake was significantly greater at week 16 for HABIT-ID than HABIT-SD, whereas urea hydrolysis at week 16 was greater for HABIT-SD than HABIT-ID and urea excretion at week 32 was greater for HABIT-ID than HABIT-SD . The combined results for HABIT-ID and HABIT-SD showed a significant reduction in urea production at week 32 compared with week 24. Urea excretion decreased significantly from week 16 to week 24 with no further decrease to week 32 and urea hydrolysis was significantly greater at week 24 than either week 16 or week 32. Compared with HABIT, on CONTROL there was a decrease in urea production at week 16, and urea excretion was significantly reduced at week 16. For all time periods urea production was closely related to the sum of intake plus hydrolysis. Hydrolysis was greatest at week 24 and closely related to urea production. There was a significantly inverse linear relationship overall for hydrolysis as a proportion of production and excretion as proportion of intake. The results show that on HABIT N is more effectively conserved in mid-pregnancy through an increase in urea hydrolysis and salvage, and during late pregnancy through a reduction in urea formation. Lowering protein intake at any stage of pregnancy increased the hydrolysis and salvage of urea. The staging of these changes was later than that in pregnancy in Jamaica.(AU)

Comparison of urinary 5-L-oxoproline (L-pyroglutamate) during normal pregnancy in women in England and Jamaica

Urinary 5-L-oxoproline was measured during normal pregnancies in Southampton, England and Kingston, Jamaica. The CV of 5-L-oxoproline excretion in urine, determined over 7 d in a non-pregnant woman and three pregnant women, was 10-36 percent. Compared with non-pregnant women, urinary 5-L-oxoproline increased three to four times from early pregnancy in women in Southampton, a highly significant difference, and remained elevated at similar levels during mid and late pregnancy. For women in Kingston, the excretion of 5-L-oxoproline was similar to that of Southampton women in the non-pregnant group and during early pregnancy. However, there was a progressive increase in the excretion of 5-L-oxoproline as pregnancy advanced and by late pregnancy excretion was from three to ten times greater than the average for the non-pregnant women. There was a significant difference between the women in Southampton and the women in Kingston during mid and late pregnancy, with women in Kingston excreting twice as much 5-l-oxoproline during late pregnancy. If the excretion of 5-L-oxoproline is a measure of glycine insufficiency, the results would indicate that in some pregnancies the ability of the mother to provide glycine for herself and the developing fetus is marginal or inadequate and the constraint appears more marked in Jamaica than in England.(AU)

Urea kinetics varies in Jamaican women and men in relation to adiposity, lean body mass and protein intake

OBJECTIVE: We have measured urea kinetics in normal adult men and women of different body composition to determine whether adiposity is associated with differences in the rate of urea production or endogenous urea hydrolysis. DESIGN: Urea kinetics were determined from the excretion of [15N15N] urea in urine over a period of 48 h following a single oral dose of [15N15N] urea, in nine lean and nine obese women and in seven light and seven heavy males while they were consuming their habitual diets. Urinary 5-L-oxoproline was measured as an index of glycine metabolic status. SETTING: The studies were carried out in the research ward of the Tropical Metabolism Research Unit, University of the West Indies. RESULTS: Successful studies were completed in eight obese and five lean women and in six heavy and five light men. When compared with lean women, in obese women the rate of urea production and hydrolysis was significantly greater and this difference could not be accounted for by the greater fat-free mass alone, and was in part associated directly with the increase in fat mass. The rate of urea production and hydrolysis was greater in heavy men than in light men, a difference which was attributed to an increase in dietary protein. In obese women and heavy men there was a significantly higher rate of excretion of 5-Loxoproline in urine when compared with lean women and lean men respectively. CONCLUSION: This paper highlights the difficulty in identifying an appropriate reference with which to express results in people of different body composition. In obese women urea production and the hydrolysis of urea are increased, in part related to the increase fat-free mass, but also related to the increased fat mass itself. In obese women and men on high protein diets the greater rate of hydrolysis urea may be a reflection of an increased demand for the sythesis of non-essential amino acids, especially glycine.(AU)

Foetal growth and increased urinary excretion of 5-oxoproline in Trinidadian infants

Size at birth is related to the risk of heart disease, hypertension and diabetes mellitus in later life. Glycine is a conditionally essential amino acid during the perinatal period. The urinary execretion of 5-1-oxoproline has been used as a marker for glycine sufficiency. In Jamaican infants, excretion increased progressively during the first weeks of life and by 6 weeks of age was two-to-three times that seen in infants in the UK. We measured the rate of excretion in 42 infants aged 4-to-6 weeks, delivered at Mount Hope Maternity Hospital (Indian, 17; African, 15; mixed, 10), compared with 22 Caucasian infants born in Southampton. There were no differences between the groups in maternal age, maternal haemoglobin, or parity. Trinidadian infants were statistically significantly lighter, with smaller head circumference than the infants in UK. The differences in weight were more marked for the Indian and mixed infants than for the African infants, although head circumference in the three groups was similar. There was a highly statistically significant increase in the excretion of 5-oxoproline in all groups of Trinidadian infants, compared with UK infants. Maternal haemoglobin related to newborn size. When maternal haemoglobin was controlled, there was a statistically significant inverse relationship between 5-oxoproline excretion and birthweight (r=-0.32, p=0.02) and head circumference (r=-0.27, p=0.05). Infants in Trinidad had levels of urinary 5-oxoproline similar to those found previously in Jamaica and about twice those seen in infants in the UK. These differences do not appear to be accounted for by infant feeding patterns, but may be directly related to aspects of maternal nutrition, and the shape and size of the infant at birth. The data suggest that the availability of glycine might be limiting for foetal growth in the Caribbean, and this could have important implications for the development of diabetes mellitus, hypertension and heart disease in later life (AU)

Urea production and salvage during pregnancy in normal Jamaica women

The pattern of aggregated nitrogen demand during pregnancy and the fetal and maternal components are unclear. Excess demand enhances efficiency of nitrogen utilization. Urea salvage contributes to enhanced efficiency. Dietary protein intake, urea production, and salvage of urea nitrogen were measured in eight nonpregnant control subjects, and trimesterly in nine pregnant women. Production was measured after prime-intermittent intravenous doses of [15N15N]-urea by dilution of label in urinary urea. Dietary protein intake was greater in trimester 1 than in nonpregnant women (167 ñ 36 vs 224 ñ 60 mg N.kg-1.d-1), and increased further in trimester 2 (266 ñ 59 mg N.kg-1.d-1). Urea production was not higher during pregnancy. Despite higher protein intake urea salvage was higer in pregnancy (40 ñ 24 nonpregnant vs 77 ñ 23, 61 ñ 31, and 51 ñ 12 mg N.kg-1.d-1). Therefore, the demand-supply gap for nitrogen was greatest early in pregnancy when fetoplacental growth is slowest, and implies heightened maternal demand (AU)

The effect of the level of dietary protein, carbohydrate and fat on urea kinetics in young children during rapid catch-up weight gain

The kinetics of urea metabolism were measured in children recovering from severe malnutrition. For a period of up to 10 d they receive one of four diets which provided 711 kj (170 kcal)/kg per d. Two groups received a diet with a high protein:energy (P:E) ratio of 10.6 percent (HP), enriched with either fat (HP/F) or maize starch and sucrose HP/C). Two groups received a diet with a low P:E ratio of 8.8 percent (LP), enriched with either fat (LP/F) or maize starch and sucrose (LP/C). The rate of weight gain on the HP diets was significsntly greater than on the LP diets. There was no difference in urea production between any of the four diets: HP/F 1.23 (se 0.12), HP/C 1.37 (se 0.14), LP/F 1.64 (se 0.22) LP/C 1.15 (se 0.15) mmol nitrogen/kg per h. On the HP diets urea excretion was 0.77 (se0.07) mmol N/kg per h, 61 percent of production. There was significantly less urea excreted in the urine on diet LP/C than on LP/F (0.36 (se0.05) and 0.64 (se 0.04)mmol N/kg per h respectively). A significantly greater percentage of the urea production was hydrolysed on the LP diets (61 percent) compared with the HP diets (39 percent), with the consequence that 50 percent of urea-N produced was available for synthetic activity on the LP diets compared with 30 percent on the HP diets. The increase in the urea hydrolysed on the LP diets was equivalent in magnitude to the decreased intake of N, so that overall intake plus hydrolysis did not differ between the LP and HP diets. Crude N balance was similiar on diets HP/F, HP/C and LP/C, but was significantly reduced on diet LP/F. These results show that there is an accommodation in urea kinetics during rapid catch-up weight gain, which becomes evident when the P:E ratio of 8.8 percent, protein is limiting for catch-up growth. When the intake has a P:E ratio of 8.8 percent the pattern of urea kinetics can be modified by the relative proportion of fat and carbohydrate in the diet. The measurement of urea kinetics provides a useful approach to the definition of the adequacy of the protein in the diet. (AU)

The excretion of 5-oxoproline in urine, as an index of glycine status, during normal pregnancy

The urinary excretion of 5-oxoproline, which may be used as an index of glycine status, was investigated in 30 normal pregnant women during different stages of pregnancy and in 18 non-pregnant female volunteers. During an 18-h study there was little variation in the 5-oxoproline/creatinine index,and a single sample gave a representative value. The excretion of 5-oxoproline/creatinine (umol/mmol) rose progressively as preqnancy advanced (non-pregnant mean 10, SD 5, first trimester mean 46, SD 12, second trimester mean 150, SD 180,and third trimester mean 280, SD 320) and by the third trimester was over 20 times greater than in non-pregnant women. The data suggest that as pregnancy advances the endogenous production of glycine may be insufficient to satisfy the increasing demands (Summary)

Whole-body protein turnover in man determined in three hours with oral or intravenous 15N-glycine and enrichment in urinary ammonia

Studies were carried out in eight normal adults to simplify the continuous infusion-end product method for measuring whole-body protein turnover using 15 N-glycine. When a priming dose of label suitable for the urea pool was followed by intermittent oral doses of label, plateau enrichment was maintained in urinary urea and ammonia from 9 to 18 h, giving values for nitrogen flux. (18h) of 0.69ñ0.05 g N/kg/d with urea and 0.46ñ0.01 g N/kg/d with ammonia. With a priming dose appropriate for the ammonia pool, plateau was reached in urinary ammonia in less than 120 min an maintained for up to 6h. Nitrogen flux (3h) with oral 15N-glycine was 0.96ñ0.12 g N/kg/d, and with intravenous label was 0.61ñ0.13 g N/kg/d. There was a significant linear relationship between flux measured with oral and intravenous isotope. It is suggested that different components of protein turnover are measured with the different approaches, and that the short method in particular measures rapidly turning over proteins associated with the gastrointestinal tract.(AU)

Effect of glycine supplementation on the pyroglutamic aciduria during recovery from severe malnutrition - abstract

We have previously demonstrated that as benzoic acid conjugates with endogenous glycine to form hippuric acid, the resulting glycine debt is associated with an increased pyroglutamic acid (PGA) excretion. We concluded that PGA could be used as an index of glycine insufficiency. Glycine is a substrate for glutathione (GSH) synthesis and PGA is an intermediate of the gamma-glutamyl cycle in which GSH is formed. As demand for glycine is enormous during periods of rapid growth, we supplemented glycine (127 mg/kg/d) to five rapid growing children (weight gain > 10g/kg/d) during recovery from severe malnutrition. Urinary PGA and blood GSH were measured before and after supplementation. SUBJECT 1: Diagnosis - kwashiorkor, Age - 18, Wt - 7.34, Change PGA - -73, Change GSH - +6.6; SUBJECT 2: Diagnosis - Mar/kwash, Age - 23, Wt - 6.55, Change PGA - -233, Change GSH - +7.6; SUBJECT 3: Diagnosis - mar/kwash, Age - 10, Wt 7.89, Change PGA - -55, Change GSH - +10.4; SUBJECT 4: Diagnosis - undernourished, Age - 14, Wt - 7.93, Change PGA - -53, Change GSH - +8.2; SUBJECT 5: Diagnosis - marasmus, Age - 12, Wt - 6.39, Change PGA - 0, Change GSH - + 4.9; SUBJECT 6: Diagnosis - kwashiorkor, Age - 14, Wt - 7.89, Change PGA - +245, Change GSH - -8.7. In four of the subjects, PGA decreased after supplementation while there was a concomitant increase in GSH. One showed no change in PGA excretion and had stopped growing. The other child showed the opposite result. PGA is usually associated with a deficiency of the enzyme GSH synthetase which is reponsible for the synthesis of GSH from glycine and glutamylcysteine. Our results support the hypothesis that if the availability of glycine were low then the reaction catalysed by GSH synthetase would be reduced because of limited substrated, and that the mechanism is effectively the same as with an absence of the enzyme - that is an increased PGA excretion. In this case, glycine corrects the defect. Furthermore, the data provide evidence that rapidly growing children may have an increased requirement for glycine (AU)

Glycine metabolism: the effect of benzoic acid on pyroglutamic acid excretion - abstract

Pyroglutamic acid is an intermediate of the r-glutamyl cycle for glutathione synthesis. Inhibition of the pathway, due to deficiency of the enzyme glutathiione synthetase, has been shown to result in accumulation and increased excretion of pyroglutamic acid. Glutathione synthetase requires glycine as a substrate, and we reasoned that limited availability of glycine may also cause increased urinary excretion of pyroglutamic acid. We therefore investigated whether pyroglutamic acid excretion rate might provide an index of glycine insufficiency. Benzoic acid readily combines with glycine to form hippuric acid, which is ultimately excreted. Therefore, benzoic acid, administration should drain the endogenous glycine pool, thus providing inadequate substrate for glutathione synthesis, and causing increased pyroglutamic acid excretion. We gave benzoic acid, and the benzoic acid for all subjects ranged between 20 and 26 æmol/mmol creatinine. Two hours after oral benzoic acid, the urinary pyroglutamic acid had increased to 42 æmol/mmol creatinine and remained elevated for the next 4 hrs., at 38 æmol/mm creatinine. When glycine was given with the benoic acid, the pyroglutamic acid reached a maximum of 37 æmol/mmol creatinine in 2 hours, and fell rapidly over the next 4 hours to 25 æmol/mmol creatinine. The levels had returned to initial values by eight hours. Levels of hippuric acid were increased with benzoic acid administration and there was a further increase when the glycine supplement was given. These data show that benzoic acid conjugates with endogenous glycine to form hippuric acid, and that the presumed glycine deficit is associated with increased pyroglutamic acid excretion. We suggest that pyroglutamic acid excretion rate could therefore be used as an index of glycine insufficiency (AU)

Studies of whole body protein turnover within three hours in man using 15 N-glycine as tracer and urinary ammonia as end-product - abstract

We have been investigating ways in which to simplfy the method for measuring proteing turnover, by shortening the time required for reliable measurements. It has been possible, using 15N-Glycine and urinary ammonia as the end-product, to measure turnover in two to three hours in normal man. Turnover was calculated following either oral or continuous infusion of 15N-Glycine (0.005 15N/kg/h) in 8 adult men. Plataeu was reached within 120 minutes and was maintained for at least 4 to 6 hours. The results were as follows: AMMONIA ENRICHMENT: Oral dose - turnover (mgN/kg/D) 960ñ128 (SD), synthesis (gPr/kg/D) 4.7ñ0.7, breakdown (gPr/kg/D) 4.9ñ0.8; AMMONIA ENRICHMENT: I.V. dose turnover - (mgN/kg/D) 608ñ128, synthesis (gPr/kg/D) 3.1ñ0.8, breakdown (gPr/kg/D) 2.8ñ0.8. There was a significant linear relationship between ammonia enrichment (oral) and ammonia enrichment (I.V.) (R=0.82; p<0.05). In the same group, turnover measured from ammonia enrichment over 18 hours was 450 ñ 30mg N/kg/D. Turnover measured over 3 hours thus gave higher values than measurements over 18 hours; this is probably because more proteins with shorter half-lives are included in the 3 hour measurements. This would imply that previously reported measurements which used the longer measurement period underestimated turnover by at least 50 percent, and hence significantly underestimated the contribution of protein turnover to basal energy expenditure. The (3 hr) oral measurement appears to measure flux through a pool not included in the measurement intravenously. As this is of a similar magnitude to the pool into which hydrolysed urea nitrogen passess (Jackson et al, Hum. Nutr. Clin. Nutr., 38C, 339, 1984) it may represent a distinct enterohepatic pool of metabolic nitrogen (AU)

Whole-body protein turnover in Jamaican women during normal pregnancy

A cross-sectional study was carried out among 18 Jamaican pregnant women divided in three groups of 6 subjects according to the stage of pregnancy: group B, 12 weeks, group C, 24 weeks and group D, 33 weeks. A group (group A) of 6 non-pregnant women was selected as control. The rate of whole-body protein turnover was measured by continuous oral administration of 15N-glycine and the resting metabolic rate by the open circuit method. All subjects had a normal pregnancy outcome. The composition of the diet on the day of the study was comparable between the four groups (approximately 80 g protein and 9.45 MJ energy) and not significantly different from the composition of the diet during the 2 d prior to the experiment. The rates of protein synthesis and breakdown were higher in groups Band C compared to group A and lower in group D where they reached values slightly higher than in group A. Estimated from urea enrichment, these rates did not vary significantly among the groups, while estimated from ammonia enrichment the difference was significant (P less than 0.05) and there was a negative correlation between the gestational age and the rate of snythesis (r= -0.63) and breakdown (r= -0.69). Nitrogen retention was comparable between the three groups of pregnant women and significantly higher than in the group A. The resting metabolic rate was similar between the groups of pregnant women. These results suggest that the rates of protein turnover observed during gestation reflect more the changes that occur in maternal than those in fetal tissues. The values for protein synthesis and nitrogen retention indicate that the amount of protein deposited during pregnancy is greater than that expected on the basis of body composition analysis. It is also suggested that as pregnancy proceeds whole-body protein turnover represents a smaller part of the resting metabolic rate. (AU)

Pyroglutamic aciduria of pregnancy: an index of glycine insufficiency? - abstract

We have shown that in preterm infants, and during the third trimester of pregnancy, there is a limited flow of isotopic glycine nitrogen to urea. We interpreted this as indicating that the large metabolic demand for glycine made by the rapidly growing foetus exceeded the ability of the body to produce glycine endogenously. In pyroglutamic aciduria, an inborn error of metabolism, a deficiency of glutathione synthetase results in an increased urinary excretion of pyroglutamic acid. We reasoned that limited availability of glycine, a substrate of glutathione synthetase, would restrict flow through this enzyme and might thus result in increased urinary excretion of pyroglutamic acid. We have measured the urinary excretion of pyroglutamic acid in non-pregnant and pregnant women in the 1st, 2nd and 3rd trimester. There was a relatively small dirunal variation in pyroglutamic acid/creatinine and a single urine gave a representative value. The pyroglutamic acid excretion rose progressively as pregnancy advanced and by the third trimester was over 20 times greater than in the non-pregnant women. As only a portion of the pyroglutamic acid produced is normally excreted in the urine, it is not possible to exclude the possibility that the increased excretion reflects a change in the metabolism of pyroglutamic acid unrelated to glycine metabolism. However, we have found that in four different metabolic states in which the demand for glycine is enhanced, there is an increased pyroglutamic acid excretion. These results provide support for the postulate that glycine acts as a semi-essential amino acid, and suggest that the availability of glycine may be limited as pregnancy advances (AU)

The use of 15 N-alanine as a tracer to measure whole body protein turnover (WBPT) in man - abstract

A preliminary study was designed to determine the most suitable metabolic condition (fed, fasted) and appropriate time (day, night) to measure whole body protein turnover. A primed intermittent oral dose of the tracer was given; urinary ammonia and urea were used as end-products. With feeding, an isotopic steady state was maintained but upon withdrawal of food it was disrupted. Also, as fasting progressed, the enrichment in urinary ammonia and urea kept increasing. This indicates that alanine did not seem to be a good tracer to measure WBPT under metabolic conditions, where the intake of food was not constant. In the fed state, rates of WBPT were measured after a primed, intermittent oral dose and after a primed, continuous intravenous infusion. Six subjects were used in the oral study and two of the six subjects were chosen for the intravenous study. During the oral administration, mean rate of WBPT as measured by the enrichment in urinary ammonia and urea, was found to be 2.25 ñ .2 gm protein/kg/day and 3.00 ñ .4 gm protein/kg/day respectively. The value obtained from the intravenous study was 1.87 gm protein/kg/day with ammonia and 4.57 gm protein/kg/day with urea. The results show that, within studies estimates of protein flux from ammonia and urea generally were not comparable, oral doses gave higher estimates with ammonia whereas the intravenous dose gave higher estimates with ureas. In contrast with the most commonly used tracer (15 N-glycine), 15N-alanine gave estimates that were lower when the respective technique and end product was considered. However, the rank order of these values for the different method was similar to those with 15 N-glycine (AU)

Studies of 15N-alanine metabolism in man: estimation of whole body protein turnover rates, alanine flux, de novo synthesis of alanine contribution to urinary ammonia

A primed intermittent oral dose and a primed continuous intravenous infusion of 15N-alanine was administered to healthy males to determine the rates of protein turnover, synthesis and breakdown. The subjects were fed an adequate intake throughout the day. Urine and blood samples were collected. Mean rate of protein flux as measured by the enrichment of urinary ammonia and urea were found to be 2.25ñ.21 and 3.00ñ.42 g. protein/kg./day respectively during the total administration. The values obtained from the intravenous study were 1.87 g. protein/kg./day with ammonia and 4.57 g. protein/kg./day with urea. When each end product and the respective technique was considered the mean rate obtained using 15N-alanine was lower than that reported using 15N-glycine. However, the rank order of the values for the different methods was similar to those with 15N-glycine. Mean plasma alanine flux after the oral and intravenous studies were 548 ñ128 and 281 æmol/kg./hr. respectively. Red cells alanine flux was different and higher than plasma flux in each study. During the studies a considerable amount of label was transferred to urinary ammonia and urea while glutamate and alanine had low enrichments. In the fed state, after the oral dose, de novo alanine synthesis was calculated to be 457.4 æmol/kg./hr. This accounted for eighty-three percent of plasma alanine flux, thus seventeen percent of alanine moving through the venous plasma compartment originated from performed alanine. Up to sixteen to twenty-two percent of urinary ammonia was derived from alanine (Summary)