Elevation of plasma epinephrine concentrations inhibits proteolysis and leucine oxidation in man via beta-adrenergic mechanisms

Anabolic Resistance in the Pathogenesis of Sarcopenia in the Elderly: Role of Nutrition and Exercise in Young and Old People

The development of sarcopenia in the elderly is associated with many potential factors and/or processes that impair the renovation and maintenance of skeletal muscle mass and strength as ageing progresses. Among them, a defect by skeletal muscle to respond to anabolic stimuli is to be considered. Common anabolic stimuli/signals in skeletal muscle are hormones (insulin, growth hormones, IGF-1, androgens, and β-agonists such epinephrine), substrates (amino acids such as protein precursors on top, but also glucose and fat, as source of energy), metabolites (such as β-agonists and HMB), various biochemical/intracellular mediators), physical exercise, neurogenic and immune-modulating factors, etc. Each of them may exhibit a reduced effect upon skeletal muscle in ageing. In this article, we overview the role of anabolic signals on muscle metabolism, as well as currently available evidence of resistance, at the skeletal muscle level, to anabolic factors, from both in vitro and in vivo studies. Some indications on how to augment the effects of anabolic signals on skeletal muscle are provided.

The impact of catecholamines on skeletal muscle following massive burns: Friend or foe?

Profound skeletal muscle wasting in the setting of total body hypermetabolism is a defining characteristic of massive burns, compromising the patient's recovery and necessitating a protracted period of rehabilitation. In recent years, the prolonged use of the non-selective beta-blocker, propranolol, has gained prominence as an effective tool to assist with suppressing epinephrine-dependent burn-induced hypermetabolism and by extension, blunting muscle catabolism. However, synthetic β-adrenergic agonists, such as clenbuterol, are widely associated with the promotion of muscle growth in both animals and humans. Moreover, experimental adrenodemedullation is known to result in muscle catabolism. Therefore, the blunting of muscle β-adrenergic signaling via the use of propranolol would be expected to negatively impair muscle protein homeostasis. This review explores these paradoxical observations and identifies the manner by which propranolol is thought to exert its anti-catabolic effects in burn patients. Moreover, we identify potential avenues by which the use of beta-blocker therapy in the treatment of massive burns could potentially be further refined to promote the recovery of muscle mass in these critically ill patients while continuing to ameliorate total body hypermetabolism.

Effects of adrenaline on lactate, glucose, lipid and protein metabolism in the placebo controlled bilaterally perfused human leg

AIM

Adrenaline has widespread metabolic actions, including stimulation of lipolysis and induction of insulin resistance and hyperlactatemia. Systemic adrenaline administration, however, generates a very complex hormonal and metabolic scenario. No studies employing regional, placebo controlled and adrenaline infusion exist. Our study was designed to test the hypothesis that local placebo controlled leg perfusion with adrenaline directly increases local lactate release, stimulates lipolysis, induces insulin resistance and leaves protein metabolism unaffected.

METHODS

  We studied seven healthy volunteers with bilateral femoral vein and artery catheters during 3-h basal and 3-h hyperinsulinemic (0.6 mU kg(-1) min(-1) ) euglycemic clamp conditions. One femoral artery was perfused with saline and the other with adrenaline (0.4 μg min m(-2) ). Lipid metabolism was quantified with [9,10-(3) H] palmitate and amino acid metabolism with (15) N-phenylalanine and lactate and glucose by raw arterio-venous differences.

RESULTS

  Femoral vein plasma adrenaline increased ≈eightfold in the perfused leg with unaltered blood flows. Adrenaline perfusion significantly increased local leg lactate release from 0.01 to 0.25 mmol min(-1) per leg, palmitate release in the basal state 11.5-16.9 μmol min(-1) per leg and during the clamp 2.62-8.44 μmol min(-1) per leg. Glucose uptake decreased during the clamp from ≈180 to 30 μmol min(-1) per leg. Phenylalanine kinetics was not affected by adrenaline.

CONCLUSION

  Adrenaline directly increases lactate release and lipolysis and inhibits insulin-stimulated glucose uptake in the perfused human leg. Adrenaline has no direct effects on peripheral amino acid metabolism. Adrenaline-induced lactate release from striated muscle may be an important mechanism underlying hyperlactatemia in the critically ill.

Effects of adiposity and 30 days of caloric restriction upon protein metabolism in moderately vs. severely obese women

Protein metabolism adapts during caloric restriction (CR) to minimize protein loss, and it is unclear whether greater fat stores favorably affect this response. We sought to determine whether protein metabolism is related to degree of obesity and whether the response to CR is impacted by pre-CR adiposity level. Whole body protein metabolism was studied in 12 obese women over a wide range of BMI (30-53 kg/m(2)) as inpatients using [1-(13)C]leucine as a tracer following 5 days of a weight-maintaining diet and then after 30 days of CR (1,400 kcal deficit with maintained protein intake). When expressed as total rates, per body weight (BW) or per fat-free mass (FFM), leucine rate of appearance (Ra), and nonoxidative leucine disposal (NOLD) were significantly higher in the individuals with a greater degree of obesity (P < 0.05). Leucine oxidation (Rox) was also higher in more highly obese women when expressed as a total rate (P < 0.05) but not if expressed per BW or FFM. CR reduced BW, FFM, and fat mass (P < 0.001), and declines were relatively similar between individuals. CR reduced Ra (P < 0.001), NOLD (P < 0.01), and Rox (P < 0.05), and the relative decline was not affected by differences in fat mass. CR-induced declines were significant even when Ra and NOLD were normalized to BW or FFM. We conclude that fat mass, like FFM, is a key determinant of protein turnover. However, during CR, higher fat mass does not favorably alter the response of protein metabolism and does not mitigate the loss of FFM.

Acute β-adrenergic stimulation does not alter mitochondrial protein synthesis or markers of mitochondrial biogenesis in adult men

Exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) is dramatically inhibited in mice pretreated with a β-adrenergic receptor (β-AR) antagonist, suggesting that β-ARs play an important role in the regulation of skeletal muscle PGC-1α expression, and potentially, mitochondrial biogenesis. Accordingly, we hypothesized that acute β-AR stimulation would induce transcriptional pathways involved in skeletal muscle mitochondrial biogenesis in humans. Whole body protein turnover (WBPT), myofibrillar protein synthesis (MyPS), skeletal muscle mitochondrial protein synthesis (MiPS), and mitochondrial biogenic signaling were determined in samples of vastus lateralis obtained on two separate occasions in 10 young adult males following 1 h of continuous intravenous administration of saline (CON) or a nonspecific β-AR agonist [isoproterenol (ISO): 12 ng·kg fat free mass−1·min−1], combined with coinfusion of [1,2]13C-leucine. β-AR stimulation induced appreciable increases in heart rate and systolic blood pressure (both P < 0.001) but did not affect mitochondrial biogenic signaling (no change in PGC-1α, TFAM, NRF-1, NRF-2, COX, or NADHox expression via RT-PCR; P > 0.05). Additionally, MiPS [CON: 0.099 ± 0.028, ISO: 0.074 ± 0.046 (mean ± SD); P > 0.05] and MyPS (CON: 0.059 ± 0.008, ISO: 0.055 ± 0.009; P > 0.05), as well as measures of WBPT were unaffected. On the basis of this investigation, we conclude that acute intravenous β-AR stimulation does not increase mitochondrial protein synthesis or biogenesis signals in skeletal muscle.

Recombinant human growth hormone improves muscle amino acid uptake and whole-body protein metabolism in chronic hemodialysis patients

BACKGROUND

Intradialytic parenteral nutrition (IDPN), with or without exercise, has been shown to reverse the net negative whole-body and forearm muscle protein balances observed during hemodialysis. Pharmacologic doses of recombinant human growth hormone (rhGH) constitute another potential anabolic therapy in chronic hemodialysis patients.

OBJECTIVE

Our goal was to examine the potential additive anabolic effects of rhGH compared with IDPN and exercise on protein and energy homeostasis.

DESIGN

We studied 7 chronic hemodialysis patients in a crossover design study in which each subject participated in 2 protocols: GH (rhGH + IDPN + exercise) and no GH (IDPN + exercise). During the GH protocol, the subjects were studied after 3 daily doses of rhGH. Each subject was studied 2 h before, 4 h during, and 2 h after a hemodialysis session with the use of a primed, constant infusion of l-[1-(13)C]leucine.

RESULTS

Whole-body net protein balance was -0.50 +/- 0.07 mg x kg fat-free mass(-1) x min(-1) when the patients did not receive rhGH and -0.39 +/- 0.04 mg x kg fat-free mass(-1) x min(-1) when the patients received rhGH, a 22% improvement in prehemodialysis whole-body protein homeostasis (P < 0.05). Essential amino acid muscle loss was also significantly less during the prehemodialysis period when rhGH was administered (-18 +/- 23 compared with -71 +/- 20 mmol/L; P < 0.05). The whole-body anabolic effects of rhGH observed during the prehemodialysis period persisted throughout the entire study, as evidenced by a lack of significant interaction or main effect of treatment during hemodialysis and in the posthemodialysis period.

CONCLUSION

rhGH improves whole-body protein homeostasis in chronic hemodialysis patients.

Adrenalectomy enhances the insulin sensitivity of muscle protein synthesis

After confirming that adrenalectomy per se does not affect skeletal muscle protein synthesis rates, we examined whether endogenously produced glucocorticoids modulate the effect of physiological insulin concentrations on protein synthesis in overnight-fasted rats 4 days after either a bilateral adrenalectomy (ADX), ADX with dexamethasone treatment (ADX + DEX), or a sham operation (Sham; n = 6 each). Rats received a 3-h euglycemic insulin clamp (3 mU. min(-1). kg(-1)). Rectus muscle protein synthesis was measured at the end of the clamp, and the phosphorylation states of protein kinase B (Akt), eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), and ribosomal protein S6 kinase (p70(S6K)) were quantitated before and after the insulin clamp. The basal phosphorylation states of Akt, 4E-BP1, and p70(S6K) were similar between ADX and Sham rats. Insulin significantly enhanced the phosphorylation of Akt (P < 0.03), 4E-BP1 (P = 0.003), and p70(S6K) (P < 0.002) in ADX but not in Sham rats. Protein synthesis was significantly greater after insulin infusion in ADX than in Sham rats (P = 0.01). Glucocorticoid replacement blunted the effect of insulin on Akt, 4E-BP1, and p70(S6K) phosphorylation and protein synthesis. In conclusion, glucocorticoid deficiency enhances the insulin sensitivity of muscle protein synthesis, which is mediated by increased phosphorylation of translation initiation-regulatory proteins.

β-Adrenergics enhance brain extraction of levodopa

We sought to determine whether beta-adrenergic agonists enhance the brain extraction of L-dopa and L-leucine. Systemic administration of beta-adrenergic agonists increase brain concentrations of L-dopa and other large neutral amino acids (LNAA) in rats and monkeys and may improve symptoms and reduce daily L-dopa requirement in patients with Parkinson's disease. Cerebral blood flow (CBF) using [3H]nicotine and the extraction fraction of 14C-labeled L-dopa or L-leucine were measured simultaneously in various brain regions of conscious rats using the dual-isotope indicator fractionation technique after intraperitoneal administration of isoproterenol (a peripheral nonselective beta-adrenergic agonist), or clenbuterol (a beta2-adrenergic agonist that crosses the blood-brain barrier), or beta-adrenergic agonist preceded by nadolol (a peripheral nonselective beta-adrenergic antagonist), or saline vehicle. Both beta-adrenergic agonists increased regional brain extraction fraction of L-dopa and L-leucine tracers by 35-45%, without altering regional CBF. These changes were accompanied by about a 30% decrease in plasma branched chain LNAA concentrations. Nadolol blocked all these effects. beta-Adrenergic agonists increase the brain extraction of L-dopa and leucine, mainly by peripheral mechanisms that reduce the levels of other competing plasma LNAAs for transport. Thus, beta-adrenergic agonists might be useful in the treatment of patients with Parkinson's disease by enhancing delivery of L-dopa to the brain.

Intravenous nutrition and postnatal growth of the micropremie

There is a growing body of evidence that early nutritional practices may affect short-term growth and developmental outcome. In addition, they may play a role in determining adult health and disease. There is much that needs to be learned about safe and efficacious nutrient administration in the ELBW population; about techniques to assess the effect of different nutritional strategies; and about the long-term effects of these regimen or development outcome, growth, and disease.

Activation of the ubiquitin pathway in rat skeletal muscle by catabolic doses of glucocorticoids

To evaluate whether catabolic levels of glucocorticoids activate the ubiquitin pathway in conjunction with their known proteolytic effect in skeletal muscle, rats were injected daily with corticosterone (CTC; 10 mg/100 g body wt) for 7 days. Two peaks of urinary excretion of 3-methylhistidine (3-MH), a specific marker of myofibrillar proteolysis, were observed at days 1 and 3 (165 and 295% of controls, respectively). Levels of ubiquitin pathway mRNAs in skeletal muscle were assessed around the 3-MH peaks. In the extensor digitorum longus, a first rise of two polyubiquitin (pUb) mRNAs was seen at day 1 (183 and 162% of control for the UbB and UbC transcripts, respectively, P < 0.01). An accumulation of both E2-14k mRNAs (140%, P < 0.02, and 157% of controls, P < 0.01) and proteasome C8 subunit mRNA (222% of control, P < 0.05) was seen at day 2. A second more important peak of induction of pUb mRNA was seen at day 3 (251 and 217% of controls for the UbB and UbC transcripts, respectively, P < 0.001). All transcripts returned to near control levels by day 4. In the soleus, induction of E2-14k mRNA started at day 3 and reached 216 and 208% of controls at day 4 (P < 0.001), whereas an increase of pUb mRNA was observed at days 3 (213 and 241%, P < 0.05) and 4 (211 and 221%, P < 0.001). A rise of proteasome C8 subunit mRNA accumulation was also seen in the soleus at days 3 (217%, P < 0.05) and 4 (157%, P < 0.05). Reduced ubiquitin conjugate levels, possibly due to their rapid degradation through increased proteasome activity, were observed in both muscle types at day 3. The parallel between the catabolic effects of CTC and activation of the ubiquitin pathway in muscles of CTC-treated rats strongly suggests the involvement of this system in glucocorticoid-induced muscular atrophy.

Hormonal regulation of human muscle protein metabolism

A continuous turnover of protein (synthesis and breakdown) maintains the functional integrity and quality of skeletal muscle. Hormones are important regulators of this remodeling process. Anabolic hormones stimulate human muscle growth mainly by increasing protein synthesis (growth hormone, insulin-like growth factors, and testosterone) or by decreasing protein breakdown (insulin). Unlike in growing animals, insulin's main anabolic effect on muscle protein in adult humans is an inhibition of protein breakdown. Protein synthesis is stimulated only in the presence of a high amino acid supply. A combination of the stress hormones (glucagon, glucocorticoids, and catecholamines) cause muscle catabolism, but the effects of the individual hormones on human muscle and their mechanisms of action remain to be clearly defined. Although thyroid hormone is essential during growth, both an excess and a deficiency cause muscle wasting by yet unknown mechanisms. A greater understanding of the regulation of human muscle protein metabolism is essential to elucidate mechanisms of muscle wasting.

Acute effect of epinephrine on muscle proteolysis in perfused rat hindquarters

An acute and direct effect of epinephrine (Epi) on muscle proteolysis was investigated using a single-pass mode of rat hindquarter perfusion. The rate of tyrosine (Tyr) release at > 30 min with cycloheximide was regarded as the muscle proteolytic rate. Infusion of Epi (500 nM) to the hindquarters of fed rats led to a sharp decrease in the Tyr release to 50% within 5 min, accompanied by an increase in perfusion pressure and edema around the perfused tissues. To clarify the mechanism, alpha- and beta-antagonists were used together with Epi. A mixture of 10 microM prazosin and 10 microM yohimbine (alpha-adrenergic blockade) before or after Epi infusion completely prevented the edema development and resulted in a new steady state to 80% of the initial rate. On the contrary, 100 microM propranolol (a beta-antagonist) with Epi did not abolish the edema and caused fluctuation in Tyr release. Whether the above results are affected by changes in Tyr transport at the plasma membrane was tested by measuring Tyr efflux from the perfused muscle. Only a beta-adrenergic blockade significantly reduced the rate constant of Tyr efflux from the intracellular pool by 13%. These results suggested that the suppression of Tyr release by alpha-adrenergic activity was mainly due to the effect on Tyr efflux, whereas that by beta-adrenergic activity was not at the Tyr transport level but at the proteolysis level, demonstrating that Epi directly inhibits proteolysis of skeletal muscle via the beta-adrenoceptor.

The role of the central nervous system in modulating glucose and protein metabolism during insulin-induced hypoglycemia

We previously established that insulin-induced hypoglycemia is associated with enhanced proteolysis with the GI tract being the major contributor to this response. In the present study we examined whether brain hypoglycemia modulates the changes in amino acid and glucose kinetics during insulin-induced hypoglycemia. Studies were performed in 24 h faster conscious dogs chronically fitted with catheters in the femoral artery, portal vein, hepatic vein, femoral vein and in both carotid and vertebral arteries, and that were also fitted with permanent tracheostomies. Following a 30 min basal period insulin was infused i.v. at 300 mU/kg.h to achieve systemic hypoglycemia averaging 42 +/- 2 mg/dl. In group I (n = 6) both central and systemic (global) hypoglycemia was allowed to develop. The rate of net hepatic glucose output (NHGO) increased by 50% above basal. Plasma leucine increased from 120 +/- 12 mumol/l basally to 154 +/- 30 mumol/l during the last hour of hypoglycemia. The rate of leucine appearance into the plasma compartment (R(a)) increased from 154 +/- 30 to 200 +/- 36 mumol/kg.h and its rate of oxidation increased from 22 +/- 5 to 51 +/- 8 mumol/kg.h, while its non-oxidative rate of disposal (141 +/- 12 mumol/kg.h) did not change. Net leucine balance across the gut was neutral (6 +/- 5 mumol/kg.h) and switched to net output of 96 +/- 24 mumol/kg.h. In group II (n = 5) 10% dextrose in water was infused into both carotid and vertebral arteries to prevent profound CNS glucopenia. This was associated with a drop in NHGO.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermic effect of epinephrine: a role for endogenous insulin

The contribution of the basal insulin concentration to the metabolic response to epinephrine was measured in eight, postabsorptive, healthy volunteers before and during epinephrine (0.05 micrograms/kg fat-free mass [FFM] x min) and somatostatin (500 micrograms/h) infusion with and without insulin (0.1 mU/kg body weight [BW] x min) replacement. At basal plasma insulin concentrations, epinephrine increased oxygen consumption, heart rate, heart work, hepatic glucose production, glycogen breakdown in liver and muscle, and glucose oxidation, and the arterial plasma concentrations of glucose, lactate, and free fatty acids. Similar effects were observed during hypoinsulinemia, but epinephrine's actions on oxygen consumption and plasma concentrations of free fatty acids were disproportionally enhanced. We conclude that epinephrine-induced thermogenesis is partially inhibited by basal plasma insulin concentrations.

Effect of acute acidosis and alkalosis on leucine kinetics in man

The effects of acute pH changes on whole body leucine kinetics (1-13C-leucine infusion technique) were determined in normal subjects. Plasma insulin, glucagon, and growth hormone concentrations were kept constant by somatostatin and replacement infusions of the three hormones. When acidosis was produced by ingestion of NH4Cl (4 mmol kg-1 p.os; n = 8) arterialized pH decreased within 3 h from 7.39 +/- 0.01 to 7.31 +/- 0.01 (P less than 0.001) and leucine plasma appearance increased by 0.13 +/- 0.04 mumol kg-1 min-1 (P less than 0.02); in contrast, when alkalosis was produced by intravenous infusion of 4 mmol kg-1 NaHCO3 (n = 7, pH 7.47 +/- 0.01), leucine plasma appearance decreased by -0.09 +/- 0.04 mumol kg-1 min-1 (P less than 0.01 vs. acidosis). Whole body leucine flux also increased during acidosis compared to alkalosis (P less than 0.05), suggesting an increase in whole body protein breakdown during acidosis. Apparent leucine oxidation increased during acidosis compared to alkalosis (P = 0.05). Net forearm leucine exchange remained unaffected by acute pH changes. Plasma FFA concentrations decreased during acidosis by -107 +/- 67 mumol l-1 (P less than 0.05) and plasma glucose increased by 1.90 +/- 0.25 mmol l-1 (P less than 0.02); in contrast, alkalosis resulted in an increase in plasma FFA by 83 +/- 40 mumol l-1 (P less than 0.02; P less than 0.01 vs. acidosis), suggesting an increase in lipolysis; plasma glucose decreased compared to acidosis (P less than 0.01). The data demonstrate that acute metabolic acidosis and alkalosis, as they occur in clinical conditions, influence protein breakdown, and in the opposite direction, lipolysis.

Nutrient interactions with reference to amino acid and protein metabolism in non-ruminants; particular emphasis on protein-energy relations in man

Because the regulation of protein and energy balance is of major research interest in the nutrition and physiology of humans and animals, a selected account of interactions between protein and energy is given here, with particular emphasis on studies in human subjects. The discussion begins with reference to the relations between protein and energy intakes and nitrogen balance; selected aspects of the relations between protein dynamics and energy metabolism among the various mammalian species are then considered. This leads to a brief account of oxidative amino acid catabolism and its relevance to the assessment of amino acid requirements, particularly in adult man. It is concluded that obligatory oxidative losses of amino acids can be used to predict or approximate amino acid requirements in children and adults. The nitrogen-sparing properties of carbohydrate and lipid-derived fuels are then considered. Despite the well-known and profound, yet differential, impacts of dietary protein and energy sources, and their interactions on body protein balance, there remain wide gaps in our understanding of the mechanisms responsible for their effects, such as the quantitative and mechanistic involvement of hormones, including insulin and the counter-regulatory hormones, and the roles played by the major amino acids responsible for the interorgan transport of nitrogen and the regulation of urea production. Additional studies focusing on metabolic nitrogen trafficking would significantly enhance an understanding of how protein and energy interact to achieve the efficient utilization of dietary protein for maintenance and promotion of lean body gain.

Beta-adrenergic effects on plasma and brain large neutral amino acids are unaltered by chronic administration of antidepressants

Effects of isoproterenol (3 mg kg-1, i.p. for 60 min) and salbutamol (3, 10 mg kg-1, i.p. for 60 min) on large neutral amino acid concentrations in rat plasma and brain were assessed. Phenylalanine, leucine, isoleucine, and valine were measured by gas chromatography with electron-capture detection; tyrosine and tryptophan were measured by HPLC with electrochemical detection. These drugs induced increases in brain tryptophan, tyrosine, phenylalanine, and valine and decreases in plasma tryptophan, tyrosine, leucine, isoleucine, and valine. Effects of salbutamol (3 mg kg-1, i.p. for 60 min) were assessed following chronic administration of phenelzine sulfate and desipramine.HCl (each drug 10 mg kg-1 per day, s.c. via Alzet 2ML4 osmotic minipumps for 28 days). There were no effects of these antidepressants on basal levels of large neutral amino acids in brain and plasma. In both brain and plasma, salbutamol-induced changes in large neutral amino acids were unaffected by these antidepressants. The results indicate that beta-adrenoceptor-regulated availability of plasma and brain large neutral amino acids is unaffected by chronic administration of tricyclic or monoamine oxidase inhibitor antidepressants.

Peripheral tissue energy metabolism during recovery from hypothermia after cardiopulmonary bypass: effect of amino-acid infusions

We studied the effects of amino-acid administration on the leg exchange of energy substrates and amino-acids during recovery from hypothermia after open heart surgery. Glucose (G, n = 5), glucose and conventional amino-acids (CA, n = 5) or glucose and branched chain amino-acids (BC, n = 5) were infused during recovery from hypothermia after open heart surgery. The leg exchange of energy substrates and amino-acids were measured after arrival at the intensive care unit, after rewarming, and 2h and 4h after rewarming during increasing amino-acid intake. Despite a normal stress response to surgery, reflected by increased energy expenditure and increased concentrations of insulin and catabolic hormones, amino-acids had no effect on the leg exchange of branched chain amino-acids, glutamine, alanine and energy substrates. This suggests that the transport of amino-acids and energy substrates into the cell are impaired after hypothermic cardiopulmonary bypass and intracellular substrates are utilised for the increased demand for energy during rewarming.

Protein metabolism assessed by 1-13C leucine infusions in patients undergoing bone marrow transplantation

Patients receiving cytoreductive therapy and bone marrow transplantation (BMT) are known to develop marked protein catabolism. To assess the contribution of whole body protein breakdown, amino acid oxidation and incorporation into proteins, plasma leucine kinetics (1-13C-leucine infusion technique) were determined in six patients five times within 14 days before and after cytoreductive therapy (Cyclophosphamide and total body irradiation) and marrow transplantation. Nitrogen balance became negative (-0.20 +/- 0.04 g/Kg/24 hr) after cyclophosphamide (p less than 0.01) and was -0.25 +/- 0.05 g/Kg/24 hr 7 days after BMT in spite of total parenteral nutrition. Plasma leucine concentration increased after BMT by 67% (p less than 0.0015). Leucine plasma appearance was 1.20 +/- 0.15 mumol/kg/min before treatment, it increased slightly and transiently after cyclophosphamide, and increased again from day 5 to day 7 after BMT (p less than 0.01), suggesting increased protein break-down. Leucine oxidation increased from 0.27 +/- 0.07 before therapy to 0.97 +/- 0.16 mumol/kg/min (p less than 0.02) after cyclophosphamide and BMT. Nonoxidative leucine disappearance rate decreased slightly from 0.92 +/- 0.08 to 0.75 +/- 0.16 mumol/kg/min after BMT (ns). Leucine metabolic clearance rate decreased from 11.8 +/- 1.65 before therapy to 6.9 +/- 0.70 ml/kg/min (p less than 0.02) after cytoreductive therapy. After BMT it increased again to 9.9 +/- 1.5 ml/kg/min (p less than 0.02). The results demonstrate that patients undergoing cytoreductive therapy and bone marrow transplantation develop negative nitrogen balance due to increased protein breakdown associated with increased leucine oxidation and increased metabolic clearance rate.(ABSTRACT TRUNCATED AT 250 WORDS)