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)

Fasting glucose production in the smaller of twins with epinephrine-deficient hypoglycemia

The possibility that insufficient glucose production or availability of gluconeogenic substrates could account for fasting hypoglycemia was investigated in three children with epinephrine deficiency. Each had been born the smaller of discordant identical twins, and the unaffected twins served as controls. Fasting plasma glucose production was measured by constant infusion of U-[13]C-glucose under steady-state conditions and was compared with availability of potential glucose sources estimated from respiratory calorimetry and excretory nitrogen. The average rate of glucose production was 2.6 mg/kg/min in the affected twins after they became symptomatic and 2.9 mg/kg/min in the control twins after comparable fasting. Plasma alanine was lower in the affected twins during this interval (average: 0.11 mM versus 0.16 mM), but not earlier prior to decreased plasma glucose; alanine correlated with plasma glucose in a similar way in both groups (r = 0.77). Plasma urea production was 0.30 versus 0.15 mg urea N/kg/min. The calculated availability of potential gluconeogenic amino acids was 1.2 versus 0.6 mg/kg/min. Availability of glycerol, estimated from respiratory calorimetry was 0.4 mg/kg/min in both groups. In two of the twin pairs, net oxidation of carbohydrate (glycogen) was, by design, relatively small under these conditions (0.1 and 0.4 mg/kg/min in the affected and control twins, respectively). Gluconeogenesis therefore accounted for the majority of glucose production. The unaccounted remaining major gluconeogenic source is assumed to be recycled substrates from unoxidized pyruvate. Infusion of excess alanine in these two pairs increased plasma glucose and glucose production similarly in both the affected and control twins. This change was associated with an abnormally large increase in plasma alanine. In the third twin pair, net oxidation of carbohydrate was greater in the affected twin (1.8 versus 1.3 mg/kg/min) and possible glucose sources exceeded total glucose production during hypoglycemia. Earlier during fasting, net oxidation of carbohydrate in this twin was 5.8 mg/kg/min versus 3.1 mg/kg/min in the control. Plasma glucose production measured simultaneously was 4.3 versus 3.8 mg/kg/min, being less than the rate of carbohydrtae oxidation in the affected twin. It is concluded that the abnormal fasting metabolism observed in these children with decreased epinephrine was not primarily a consequence of deficient glucose production or lack of potential gluconeogenic substrates. Initial persistent oxidation of glycogen and subsequent increased utilization of protein during hypoglycemia indicate failure to conserve these limited net sources of pyruvate(AU)

[15N]Glycine metabolism in normal man: the metabolic O-amino-nitrogen pool

[15N]Glycine was infused into fed, fasted or acidotic humans. In all metabolic states there was considerable transfer of labelled nitrogen to urea and amonia, but alanine and glutamate did not become enriched. The findings show that free exchange of nitrogen between all amino acids does not take place. Glycine, serine, threonine, lysine and histidine cannot be considered part of the a-amino-nitrogen pool as classically conceived, although they form up to one-half of that pool. (AU)

In vivo studies of amino acid, water and electrolyte transport in the small intestine of normal and magnesium depleted rats

Net amino acid, water and electrolyte transport from the small intestine in vivo was studied in normal and magnesium depleted rats, by a single pass perfusion technique. The net absorption of the amino acids, alanine and lysine increased with increasing concentration of the amino acid in the perfusion solution, within the concentration range studied (10 and 50mM). In all cases alanine was absorbed faster than lysine. Dietary magnesium depletion, lasting for a period of twenty eight days did not affect the net rate of transport of these two amino acids in any of the regions of the small intestine which were studied. In general, the presence of amino acids increased the absorption of water by comparison with that from saline. However, lysine at a concentration of 50mM tended to inhibit water absorption by comparison with that observed in the presence of alanine at 50mM. Magnesium depletion did not in general affect net transport rates of water in the presence and absence of amino acids. However, when alanine at a concentration of 50mM was perfused, water absorption was inhibited in the magnesium depleted rats. The presence of amino acids did not affect the transport of sodium in any of the regions of the small intestine. However, magnesium depletion did severely inhibit sodium transport, especially in the presence of alanine at a concentration of 50mM in all three regions of the small intestine. Amino acids stimulated the absorption of chloride by all segments of the small intestine by comparison with that from saline alone. Magnesium depletion however, significantly reduced chloride ion absorption by all three segments. Good correlations were found between the transport rates of sodium and chloride, sodium and water, and total solute and water in all three regions of the small intestine (AU)

Modification of diamine oxidase activity in vitro by metabolites of asparagine and differences in asparagine decarboxylation in normal and virus-transformed baby hamster kidney cells

The oxidation of putrescine in vitro by pig kidney diamine oxidase (EC 1.4.3.6) was increased in the presence of 2-oxosuccinamic acid and malonamic acid. It was inhibited by 3-aminopropionamide, oxaloacetate and pyruvate. 2-Oxosuccinamate was derived from asparagine in virus-transformed baby hamster kidney (BHK) cells growing in tissue culture. Asparagine was decarboxylated more efficiently by transformed than by normal BHK cells. In BHK cells transformed by polyoma virus (Py BHK), 2-oxosuccinamate is the most likely immediate precursor of the 14 CO2 arising from [U-14C] asparagine, and there was some evidence for its formation in an asparagine-dependent clone of BHK cells before and after their transformation by hamster sarcoma virus (respectivey Asn- and HSV Asn-). The relationship between 2-oxosuccinamate and pyruvate and the possible roles of these two substances in controlling cellular diamine oxidase activity are discussed (AU)

Counteraction of glucocorticoid - induced hyperglycaemia by hypoglycin

Hypoglycin, B-(methylenecyclopropyl) alanine), administered to starved rats pretreated with corticosterone, caused within 6 hr. a marked decline in blood sugar levels. The findings are evidence that the hypoglycaemic agent imposed a restriction on the rate of gluconeogenesis, against which the multiple actions of the hormone were effective. This conclusion emphasizes the crucial nature of the inhibition which hypoglycin produces in the metabolic sequence of gluconeogenesis (AU)