Compartmental model of leucine kinetics in humans

The complexity of amino acid and protein metabolism has limited the development of comprehensive, accurate whole body kinetic models. For leucine, simplified approaches are in use to measure in vivo leucine fluxes, but their domain of validity is uncertain. We propose here a comprehensive compartmental model of the kinetics of leucine and alpha-ketoisocaproate (KIC) in humans. Data from a multiple-tracer administration were generated with a two-stage (I and II) experiment. Six normal subjects were studied. In experiment I, labeled leucine and KIC were simultaneously injected into plasma. Four plasma leucine and KIC tracer concentration curves and label in the expired CO2 were measured. In experiment II, labeled bicarbonate was injected into plasma, and labeled CO2 in the expired air was measured. Radioactive (L-[1-14C]leucine, [4,5-3H]KIC, [14C]bicarbonate) and stable isotope (L-[1-13C]leucine, [5,5,5-2H3]KIC, [13C]bicarbonate) tracers were employed. The input format was a bolus (impulse) dose in the radioactive case and a constant infusion in the stable isotope case. A number of physiologically based, linear time-invariant compartmental models were proposed and tested against the data. The model finally chosen for leucine-KIC kinetics has 10 compartments: 4 for leucine, 3 for KIC, and 3 for bicarbonate. The model is a priori uniquely identifiable, and its parameters were estimated with precision from the five curves of experiment I. The separate assessment of bicarbonate kinetics (experiment II) was shown to be unnecessary. The model defines masses and fluxes of leucine in the organism, in particular its intracellular appearance from protein breakdown, its oxidation, and its incorporation into proteins. An important feature of the model is its ability to estimate leucine oxidation by resolving the bicarbonate model in each individual subject. Finally, the model allows the assessment of the domain of validity of the simpler commonly used models.

beta-Furfuryl-beta-glucoside. An endogenous activator of higher plant UDP-glucose: (1----3)-beta-glucan synthase

We have recently established the existence of endogenous activators of higher plant UDP-glucose: (1----3)-beta-glucan synthase (Callaghan, T., Ross, P., Weinberger-Ohana, P., and Benziman, M. (1988) Plant Physiol. 86, 1099-1103). Here we report the purification and chemical analysis of the most abundant and specific compound, termed Activator I, isolated from Vigna radiata. This compound was extensively purified by a multistep procedure which yielded 0.1 mg of purified activator/g of fresh tissue. Enzyme digestion, neutral sugar analysis, GC/MS of permethylated derivatives, and NMR analysis of native Activator I indicated that the compound contains a single beta-linked glucosyl residue. High resolution FAB-MS indicated an elemental composition of C11H16O7 (Mr = 260), with a calculated Mr of 98 for the aglycone. 13C, DEPT, and COSY NMR spectra showed that the aglycone molecule is an oxygen heterocycle of 5 carbons, consistent with a structure of beta-furfuryl alcohol. Comparison of IR and GC/EI-MS spectra of authentic beta-furfuryl alcohol with native aglycone confirmed the conclusion that Activator I is beta-furfuryl-beta-glucoside. Chemically synthesized beta-furfuryl-beta-glucoside has identical chemical properties and biological activity when compared with the purified endogenous activator (Ka = 50 microM).

Leucine metabolism in man: lessons from modeling

The metabolism of amino acids is far more complicated than a 1- to 2-pool model, yet, such simple models have been extensively used with many different isotopically labeled tracers to study protein metabolism. A tracer of leucine and measurement of leucine kinetics has been a favorite choice for following protein metabolism. However, administering a leucine tracer and following it in blood will not adequately reflect the complex, multi-pool nature of the leucine system. Using the tracer enrichment of the ketoacid metabolite of leucine, alpha-ketoisocaproate (KIC), to reflect intracellular events of leucine was an important improvement. Whether this approach is adequate to follow accurately leucine metabolism in vivo or not has not been tested. From data obtained using simultaneous administration of leucine and KIC tracers, we developed a 10-pool model of the in vivo leucine-KIC and bicarbonate kinetic system. Data from this model were compared with conventional measurements of leucine kinetics. The results from the 10-pool model agreed best with the simplified approach using a leucine tracer and measurement of KIC enrichment.

Identification and chromosomal locations of a family of cytochrome P-450 genes for pisatin detoxification in the fungus Nectria haematococca

The ability to detoxify the phytoalexin, pisatin, an antimicrobial compound produced by pea (Pisum sativum L.), is one requirement for pathogenicity of the fungus Nectria haematococca on this plant. Detoxification is mediated by a cytochrome P-450, pisatin demethylase, encoded by any one of six Pda genes, which differ with respect to the inducibility and level of pisatin demethylase activity they confer, and which are associated with different levels of virulence on pea. A previously cloned Pda gene (PdaT9) was used in this study to characterize further the known genes and to identify additional members of the Pda family in this fungus by Southern analysis. DNA from all isolates which demethylate pisatin (Pda+ isolates) hybridized to PdaT9, while only one Pda- isolate possessed DNA homologous to the probe. Hybridization intensity and, in some cases, restriction fragment size, were correlated with enzyme inducibility. XhoI/BamHI restricted DNA from reference strains with a single active Pda allele had only one fragment with homology to PdaT9; no homology attributable to alleles associated with the Pda- phenotype was found. Homology to this probe was also limited to one or two restriction fragments in most of the 31 field isolates examined. Some unusual progeny from laboratory crosses that failed to inherit demethylase activity also lost the single restriction fragment homologous to PdaT9. At the chromosome level, N. haematococca is highly variable, each isolate having a unique electrophoretic karyotype. In most instances, PdaT9 hybridized to one or two chromosomes containing 1.6-2 million bases of DNA, while many Pda- isolates lacked chromosomes in this size class. The results from this study of the Pda family support the hypothesis that deletion of large amounts of genomic DNA is one mechanism that reduces the frequency of Pda genes in N. haematococca, while simultaneously increasing its karyotypic variation.

Leucine kinetics from [2H3]- and [13C]leucine infused simultaneously by gut and vein

In amino acid tracer kinetic studies of the fed state, ingested amino acid may be taken up during its initial transit through splanchnic tissues and thus not enter the plasma compartment where tracer is infused. To investigate this possibility, adult human subjects received simultaneous intravenous (iv) and intragastric (ig) leucine tracer infusions, first during a postabsorptive (PA) 4-h primed continuous ig infusion of L-[1-13C]-leucine and L-[5,5,5-2H3]leucine iv, followed on a separate day by a fed infusion, in which an ig infusion of a liquid formula was started 2 h before the tracer infusion and continued throughout the tracer study. Subjects were accustomed to a constant experimental diet supplying 1.5 g protein.kg-1.day-1 and 41-45 kcal.kg-1.day-1 for 7 and 12 days before the PA and fed studies, respectively. For the PA study, plasma enrichment for the ig tracer was 3.34 +/- 0.27 (SE) mol + excess and for the iv tracer it was 4.18 +/- 0.10 (P less than 0.02). Enrichments of alpha-keto-isocaproic acid (KIC) were 3.24 +/- 0.16 (ig) and 3.02 +/- 0.14 (iv), respectively [not significant (NS)]. For the fed study, plasma leucine enrichment for the ig tracer was 2.15 +/- 0.14 and for the iv tracer was 2.84 +/- 0.09 (P less than 0.02). KIC enrichments were 2.02 +/- 0.08 (ig) and 2.24 +/- 0.08 (iv), respectively (NS). In the PA study, the ratio of the plasma leucine enrichments for the ig and iv tracers was 0.80 +/- 0.06 and in the fed experiment, 0.76 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycerol metabolism in humans: validation of 2H- and 13C-labelled tracers

For a tracer to be valid it must follow the metabolism of the tracee without distortion. Especially when the tracer contains several deuterium substitutions, the tracer can be altered or degraded differently from the metabolite it is to trace or be subject to distorting isotope effects. To determine whether 2H5-glycerol is a valid tracer for following glycerol kinetics, 2H5-glycerol and [2-13C]glycerol tracers were infused simultaneously in six healthy postabsorptive adult subjects. After 90 min of tracer infusion, epinephrine was also infused for 60 min to stimulate lipolysis and increase glycerol flux. Glycerol flux increased from 2.2 +/- 0.3 to 6.7 +/- 0.4 mumol/kg per minute (with the 13C tracer) and from 2.2 +/- 0.3 to 6.7 +/- 0.3 mumol/kg per minute (with the 2H tracer) when epinephrine was infused. There was no significant difference in glycerol flux measured with the 2H tracer compared to the 13C tracer either under basal or a stimulated flux condition. These results indicate that 2H5-glycerol is a valid tracer for measuring glycerol metabolism in humans.

Hypertonic nasogastric tube feedings: do they cause diarrhea?

Hypertonic NG tube feeding in hospitalized patients, whether on the hospital ward or in the ICU, is considered a common etiology of diarrhea. To evaluate the accuracy of this assumption, five normal volunteers, ten hospitalized postoperative patients with head and neck cancer, and 24 ICU patients were given hypertonic (690 mosm), low residue, lactose-free tube feedings starting at 30 kcal/kg.day. There was no prior history of diarrhea in any of the groups studied. There was a significant difference in albumin levels between the three groups, with an average albumin of 2.8 g/dl in the ICU patient group; different from 4.5 g/dl present in both the normal volunteer and non-ICU hospitalized patient groups (general linear models procedure from SAS, p less than .05) (Duncan test). Diarrhea was not present in the normal volunteers or non-ICU patients during the feedings, but did occur in 3/24 ICU patients. This difference was not significant. The three patients with diarrhea had an average albumin level of 3.0 g/dl, while the other ICU patients had an average albumin of 2.7 g/dl. We conclude that hypertonic NG tube feedings do not cause diarrhea in normal volunteers or postoperative head and neck cancer patients. However, in a small statistically insignificant percent of mechanically ventilated ICU patients, this regimen may cause diarrhea although no risk factors can be identified.

Biosynthesis of the Phytoalexin Pisatin : Isoflavone Reduction and Further Metabolism of the Product Sophorol by Extracts of Pisum sativum

NADPH-dependent reduction of 2',7-dihydroxy-4',5'-methylenedioxyisoflavone to the isoflavanone sophorol, a proposed intermediate step in pisatin biosynthesis, was detected in extracts of Pisum sativum. This isoflavone reductase activity was inducible by treatment of pea seedlings with CuCl(2). The timing of induction coincided with that of the 6a-hydroxymaackiain 3-O-methyltransferase, which catalyzes the terminal biosynthetic step. Neither enzyme was light inducible. Further NADPH-dependent metabolism of sophorol by extracts of Cucl(2)-treated seedlings was also observed; three products were radiolabeled when [(3)H]sophorol was the substrate, one of which is tentatively identified as maackiain.

Nitrogen sparing by 2-ketoisocaproate in parenterally fed rats

In rats receiving total parenteral nutrition with or without sodium 2-ketoisocaproate (KIC; 2.48 g.kg-1.day-1), L-[1-13C]leucine and [1-14C]KIC were constantly infused for 6 h. CO2 production, 14CO2 production, 13CO2 enrichment, urinary urea nitrogen (N) plus ammonia N and total urinary N were measured. Whole body protein synthesis (S) was calculated in non-KIC-infused rats and also in unfed rats infused with [1-14C]leucine from fractional oxidation of labeled leucine (1-F), where F is fractional utilization for protein synthesis, and urea N plus ammonia N excretion (C) as S = C x F/(1-F). Addition of KIC caused a significant reduction in N excretion and a significant improvement in N balance. Fractional oxidation of labeled KIC increased, whereas fractional utilization of labeled KIC for protein synthesis decreased, but the extent of incorporation of infused KIC into newly synthesized protein (as leucine) amounted to at least 40% of the total rate of leucine incorporation into newly synthesized whole body protein. We conclude that addition of KIC spares N in parenterally fed rats and becomes a major source of leucine for protein synthesis.

Overfeeding: cardiovascular and metabolic response during continuous formula infusion in adult humans

The cardiovascular and metabolic response to continuous nasoenteric formula infusion was monitored in eight healthy men during three consecutive 1-wk balance periods: maintenance-stabilization, overfeeding at twice the maintenance infusion rate, and postoverfeeding return to maintenance infusion. Elemental balance, thermogenic, and stable-isotope studies carried out throughout protocol identified 1) two distinct phases during overfeeding (early, days 1-4, and late, days 4-7); 2) changes in extracellular fluid (sodium balance) as the major determinant of overfeeding weight gain; 3) individual differences in percentage of excess fuels retained during overfeeding (76-87%), derived from variation in both digestive and thermogenic processes; and 4) a sustained physiologic response during the postoverfeeding period. These initial findings suggest that individuals differ in response to overfeeding and that specific aspects of this variation are amenable to future study. In addition, the timing of observed fluid, metabolic, and cardiovascular changes during overfeeding suggests specific strategies aimed at preventing refeeding circulatory complications.

L-citrulline production from L-arginine by macrophage nitric oxide synthase. The ureido oxygen derives from dioxygen

Previously proposed mechanisms for the production of L-citrulline from L-arginine by macrophage nitric oxide (NO.) synthase involve either hydrolysis of arginine or hydration of an intermediate and thus predict incorporation of water oxygen into L-citrulline. Macrophage NO. synthase was incubated with L-arginine, NADPH, tetrahydrobiopterin, FAD, and dithiothreitol in H2(18)/16O2. L-Citrulline produced in this reaction was analyzed with gas chromatography/mass spectrometry. Its mass spectrum matched that of L-citrulline generated in H2(16)O/16O2. The base fragment ion of m/z 99 was shown to contain the ureido carbonyl group by using L-[guanidino-13C]arginine as substrate. When the enzyme reaction was performed in H2(16)O/18O2, the base fragment ion shifted to m/z 101 with L-[guanidino-12C]arginine as the substrate and to m/z 102 with L-[guanidino-13C]arginine. These results indicate that the ureido oxygen of the L-citrulline product of macrophage NO.synthase derives from dioxygen and not from water.

Effect of epinephrine on amino acid and energy metabolism in humans

Epinephrine was infused for 8.5 h into five normal, healthy, young adult men on four different occasions at 0, 0.5, 1, and 2 micrograms/min to elevate circulating levels of epinephrine into the high physiological range as seen in stress and trauma. Energy expenditure, heart rate, and blood pressure were measured at hourly intervals. [1-13C]leucine, [ring-2H5]phenylalanine, and [2-15N]glutamine were infused during the last 3.5 h to follow essential amino acid and glutamine kinetics. This design was adapted to study the effects of epinephrine on energy and protein metabolism after acute and temporary metabolic responses to epinephrine had occurred. Plasma glucose was significantly increased by approximately 20 mg/dl from 83 mg/dl (saline infusion) at all levels of epinephrine infusion. Amino acid levels were depressed with epinephrine infusion, with the largest drop occurring for the essential amino acids (-27% at the 2.0-micrograms/min dose). Energy expenditure was increased with epinephrine infusion in a dose-dependent fashion (+17% increase at 2.0 micrograms/min infusion). These effects were sustained for the duration of 8.5 h epinephrine infusion. There was no significant change in leucine or phenylalanine flux, indicative of protein breakdown, or in leucine oxidation. Glutamine flux was significantly (but modestly, +7%) increased at only the 2.0-micrograms/min infusion rate. Changes in kinetics that altered amino acid levels were not apparent by 7 h of epinephrine infusion (the beginning of the plateau period for the tracer infusion study). Although epinephrine can produce long-term elevations of metabolic rate, its effects on protein metabolism are minimal beyond acute changes affecting amino acid levels.

Plasma amino acid kinetics during acute states of glucagon deficiency and excess in healthy adults

The effects of glucagon deficiency and excess on plasma leucine, lysine, and alanine were examined in six healthy young adult men, with primed continuous infusions of L-[1-13C]- or L-[5,5,5-2H3]leucine, L-[alpha-15N]-lysine, and L-[3-13C]alanine for 150 min before and during 210 min of either a glucagon-deficient euglycemic state (experiment 1), a basal glucagon state (experiment 2), or a glucagon-excess state (experiment 3). Steady-state plasma hormone levels were achieved by infusion of somatostatin (250 micrograms/h) and insulin (0.07 mU.kg-1.min-1), without (experiment 1) or with an infusion of glucagon at 0.7 ng.kg-1.min-1 (experiment 2) or 2.5 ng.kg-1.min-1 (experiment 3). Plasma branched-chain amino acid (AA) concentrations did not change with altered glucagon status, whereas significant differences were observed for plasma lysine, alanine, glycine, serine, threonine, proline, tyrosine, citrulline, and ornithine levels (0.05 greater than P greater than 0.001). Plasma leucine, lysine, and alanine fluxes and the rate of de novo alanine synthesis showed no significant changes with either glucagon deficiency or excess. These findings lead to the conclusion that glucagon-induced alterations in plasma AA profiles are not due to changes in the rate of appearance of AA from peripheral tissues but rather a consequence of changes in the fate of AA within the splanchnic region.

Peritoneal dialysis in the first 60 days of life

This report describes a 7-year experience with acute peritoneal dialysis in 31 neonates and infants less than 60 days of age. There were 20 boys and 11 girls, ages 3 to 60 days. Tenckhoff catheters of modified length were placed in the newborn intensive care unit (ICU), pediatric ICU, or surgery suites, and hourly exchanges (20 cc/kg) were started immediately postoperatively. Diagnoses included congenital metabolic disorders (11), acute tubular necrosis (6), postcardiopulmonary bypass with renal failure (5), renal cortical necrosis (5), obstructive uropathy (2), renal agenesis (1), and bilateral renal dysplasia (1). Complications included: peritonitis (4), bowel perforation (1), exit site infection (3), leaking dialysate (4), catheter obstruction (2), inguinal hernias (3), umbilical hernia (1), and retroperitoneal hemorrhage (1). There were 19 deaths (61.3%) from 1 to 90 days postinsertion in this high risk group. The (1), and post liver transplant (1). Effective dialysis (lowering of blood urea nitrogen (BUN) or ammonia, correction of acidosis, decrease in fluid overload) was possible in all cases. Five of the 12 survivors remain on chronic dialysis awaiting renal transplantation. Peritoneal dialysis is effective in the newborn period in the management of metabolic disturbances as well as renal failure. Morbidity and mortality (61.3%) is related to the near-morbid condition of the baby at the time of insertion and the severity of the complex underlying diagnosis often associated with multiorgan failure.

Purification and Characterization of S-Adenosyl-l-methionine:6a-Hydroxymaackiain 3-O-Methyltransferase from Pisum sativum

The isoflavonoid phytoalexin pisatin is synthesized by Pisum sativum in response to microbial infection and certain other forms of stress. An enzyme which synthesizes pisatin by methylating the 3-hydroxyl of (+)6a-hydroxymaackiain (HMK) was extracted from CuCl(2)-stressed pea seedlings. The enzyme was enriched 370-fold by (NH(4))(2)SO(4) precipitation, DEAE chromatography, chromatofocusing, and hydrophobic interaction chromatography (HIC), to a specific activity of 8.2 microkatals per gram protein. Enzyme activity profiles from chromatofocusing and HIC columns suggested the presence of two isozymes, of pl 5.2 and 4.9. Nondenaturing gel filtration of the HIC-purified enzyme gave a single peak of activity at the same elution volume as BSA (66 kilodaltons); the active fractions showed two proteins upon SDS-PAGE, of M(r) 66,000 and 43,000. The smaller protein was most abundant in chromatographic fractions containing peak enzyme activity throughout purification. In a partially purified preparation, this 43 kilodalton protein was the only one photoaffinity labelled by [(3)H]S-adenosyl-l-methionine. The purified enzyme preferred the (+) over the (-) stereoisomer of HMK and other pterocarpans; overall, (+)HMK was the best substrate. K(m) values were 2.3 micromolar for (+)HMK and 35 micromolar for S-adenosyl-l-methionine. The methyltransferase had a pH optimum of 7.9 and no apparent divalent cation requirement.

Stimulation of protein turnover by carbohydrate overfeeding in men

The effect of carbohydrate overfeeding on protein metabolism was studied in 11 healthy men. Total urinary nitrogen output during 10 days of carbohydrate overfeeding (1,600 extra kcal/day) decreased 27% relative to nitrogen excretion during 10 days of weight maintenance, indicating protein accretion during over-feeding. However, postabsorptive nitrogen excretion did not change, which means that the positive nitrogen balance associated with overfeeding results from enhanced postprandial nitrogen retention. Overfeeding reduced postabsorptive glucose concentrations 4 +/- 1% and increased glucose production rate 14 +/- 2% and glucose clearance 17 +/- 4%. Overfeeding increased plasma concentrations of insulin, glucagon, and 3,5,3'-triiodothyronine approximately 20%. Alanine and branched-chain amino acid concentrations were increased after overfeeding, but serine, threonine, and asparagine concentrations were reduced. Postabsorptive leucine flux, which is an index of proteolysis, was measured using L-[1-13C]leucine as a tracer. Overfeeding increased leucine flux 13 +/- 2% compared with values after 10 days on a weight-maintenance diet. If it is assumed that overfeeding did not alter the fraction of 13CO2 not recovered in breath, there was no change in the portion of leucine flux that was oxidized. Thus the difference between flux and oxidation, which is a theoretical index of protein synthesis, increased 12 +/- 3% after overfeeding. These data suggest that excess caloric intake, without an increase in protein intake, stimulates post-absorptive proteolysis and protein synthesis.

Epinephrine's effect on metabolic rate is independent of changes in plasma insulin or glucagon

Epinephrine's effect to increase metabolic rate is accompanied by changes in the plasma concentrations of insulin, glucagon, and metabolic substrates. Because both glucagon and insulin have been reported to affect thermogenesis, these hormones might contribute to or modify the thermogenic response to epinephrine. To determine if the epinephrine-induced increase in metabolic rate is secondary to changes in glucagon or insulin or to changes in the fuels modulated by these hormones, metabolic rate was measured by indirect calorimetry in five normal weight post-absorptive young men on three occasions: study A, an intravenous epinephrine infusion alone; study B, a 4-h "islet clamp" consisting of somatostatin infusion with basal insulin and glucagon replacement; and study C, an intravenous epinephrine infusion combined with the islet clamp. A 1-h base-line period preceded 2 h of epinephrine infusion. During the 4-h islet clamp (study B), metabolic rate and plasma concentrations of epinephrine, insulin, glucagon, and glucose remained unchanged. During the infusion of epinephrine alone (study A), metabolic rate and concentrations of glucagon, free fatty acids, and C-peptide increased as expected. Also as expected, the glycemic response to epinephrine infusion was much larger when insulin and glucagon levels were fixed with the islet clamp (study C). In contrast, the metabolic rate and the free fatty acid concentration responded similarly to epinephrine infusion when insulin and glucagon were fixed (study C) and when they were changing (study A). We conclude that epinephrine increases metabolic rate independently of physiological changes in plasma glucagon or insulin or the circulating fuels they modulate.

Exercise-mediated peripheral tissue and whole-body amino acid metabolism during intravenous feeding in normal man

1. The effect of a daily submaximal exercise regimen on whole-body and peripheral tissue amino acid metabolism during weight-stable intravenous feeding (IVF) was evaluated in 11 normal volunteers. Five of the subjects performed 1 h of daily bicycle exercise at 75 W during IVF, while the remaining six subjects received IVF without daily exercise. Body nitrogen balance, leg and forearm plasma amino acid flux and whole-body kinetics were measured before and on day 10 of IVF using a [1-13C]leucine and [15N]glycine tracer. 2. At the end of the IVF period, exercised subjects demonstrated leg uptake of total amino acids (237 +/- 103 nmol min-1 100 ml-1 of tissue, mean +/- SEM) which was significantly (P less than 0.05) different than in non-exercised subjects (-1101 +/- 253 nmol min-1 100 ml-1 of tissue). 3. In the non-exercised forearm, a significant (P less than 0.05) decrease in total amino acid flux was observed in exercised subjects (-162 +/- 88 nmol min-1 100 ml-1 of tissue) compared with non-exercised subjects (-460 +/- 105 nmol min-1 100 ml-1 of tissue) on day 10 of IVF. 4. Efflux of 3-methylhistidine significantly (P less than 0.05) decreased from the leg in those subjects who performed daily exercise (-0.29 +/- 0.12 nmol min-1 100 ml-1 of tissue) compared with those subjects receiving IVF without daily exercise (-1.46 +/- 0.35 nmol min-1 100 ml-1 of tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant growth hormone enhances muscle myosin heavy-chain mRNA accumulation and amino acid accrual in humans

A potentially lethal complication of trauma, malignancy, and infection is a progressive erosion of muscle protein mass that is not readily reversed by nutritional support. Growth hormone is capable of improving total body nitrogen balance, but its role in myofibrillar protein synthesis in humans is unknown. The acute, in situ muscle protein response to an infusion of methionyl human growth hormone was investigated in the limbs of nutritionally depleted subjects during a period of intravenous refeeding. A 6-hr methionyl growth hormone infusion achieved steady-state serum levels comparable to normal physiologic peaks and was associated with a significant increase in limb amino acid uptake, without a change in body amino acid oxidation. Myosin heavy-chain mRNA levels, measured by quantitative dot blot hybridization, were also significantly elevated after growth hormone administration. The data indicate that methionyl growth hormone can induce intracellular amino acid accrual and increased levels of myofibrillar protein mRNA during hospitalized nutritional support and suggest growth hormone to be a potential therapy of lean body wasting.

Leucine metabolism in aging humans: effect of insulin and substrate availability

To elucidate the relative roles of insulin (I) and amino acid (AA) availability on body protein economy and AA kinetics, we compared whole body leucine kinetic responses, using a 360-min constant infusion of L-[1-13C]leucine, during administration of an L-AA solution to six healthy young (21-25 yr) and six healthy old (72-87 yr) men (study 1) to those when the AA solution was given in conjunction with a euglycemic I clamp (study 2). In study 1, serum I increased significantly (P less than 0.02) by 4 +/- 1 and 4 +/- 2 microU/ml in young (Y) and old (O) men, respectively. In study 2, I was raised to 91 +/- 7 (Y) and 88 +/- 7 (O) microU/ml; the glucose infusion to maintain euglycemia in the Y was significantly greater than in the O (8.0 +/- 0.1 vs. 6.8 +/- 1.9 mg.kg-1.min-1). Leucine flux and oxidation increased significantly in both age groups during the administration of AA. Estimates of leucine released from protein breakdown declined (P less than 0.01) by 18 and 20% in study 1 and 2, respectively, in the young and by 12 and 44%, respectively, in the elderly. Rates of leucine incorporation into protein increased (P less than 0.01) similarly in both age groups and in both studies. These findings emphasize the importance of AA availability in the stimulation of protein synthesis and suggest that insulin's major role in vivo is to repress whole body proteolysis. Furthermore, despite evidence of an age-related decline in glucose disposal, the elderly had similar leucine kinetic responses to hyperaminoacidemia.

Evaluation of high-intensity therapeutic ultrasound irradiation in the treatment of experimental hepatoma

A study evaluating the efficacy of high-intensity therapeutic ultrasound (HITU) as a treatment modality in experimental hepatoma is reported. Morris hepatoma (3924) 1 x 10(6) cells were transferred subcutaneously into 40 male ACI rats (weight, 150 to 200 g). Animals were divided into four experimental groups: group 1 (n = 10) consisted of untreated controls; group 2 (n = 10) received intraperitoneal cyclophosphamide 50 mg/kg as a single dose; group 3 (n = 10) underwent HITU only; and group 4 (n = 10) received both chemotherapy (as in group 2) and HITU (as in group 3). HITU was administered with a 5.5-cm diameter 4-MHz quartz transducer creating a continuous wave with 400 W/cm2 focal intensity. The entire tumor was irradiated in 1-mm increments (horizontal and vertical) using treatment cycles of 4 seconds on and 11 seconds off. Total body weight and tumor volume were measured on the day of treatment, and 4 weeks later. At 4 weeks, the animals were killed, the tumor was excised and weighed, and tumor volume was determined. Tumor volume in all treated animals (groups 2, 3 and 4) was significantly smaller than in controls (P less than .001) at 4 weeks, and tumor volume for animals in group 4 was significantly smaller than for those in groups 2 and 3 (P less than .01). These data indicate that HITU significantly reduces tumor size when compared with control rats with Morris hepatoma. A synergistic effect of chemotherapy and HITU was observed and resulted in an enhanced tumor response and reduction of tumor size.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine flux in obese and healthy humans as evaluated by 15N- and 2H3-labeled alanines

Estimates of plasma alanine flux as measured in humans using L-[15N]-alanine or L-[3,3,3-2H3]alanine were compared by simultaneous intravenous infusion of both tracers. Plasma isotope enrichments were measured by chemical ionization gas chromatography-mass spectrometry. In 16 obese women before and during a hypocaloric diet and in 4 normal men in the postabsorptive and fed states, the fluxes were highly correlated (r2 = 0.93) although plasma alanine flux with the 2H tracer was two to three times greater than that obtained with [15N]alanine. The fluxes decreased with the hypocaloric diet in obese subjects and increased during the fed state in healthy adults. Thus, although the estimates of alanine flux differed according to the tracer used, both appear to give equivalent information about changes in alanine kinetics induced by the nutritional conditions examined.