Leucine Appearance Research Articles

Effect of oral citrulline supplementation on whole body protein metabolism in adult patients with short bowel syndrome: A pilot, randomized, double-blind, cross-over study

As citrulline is produced by small intestine, plasma citrulline concentration is decreased and may become essential in patients with short bowel syndrome (SBS). In a rat model of SBS, citrulline supplementation enhanced muscle protein synthesis. The aim of the study was to determine whether citrulline impacts whole body protein metabolism in patients with SBS. Nine adults with non-malignant SBS (residual small bowel 90±48cm; mean±SD) who were in near-normal nutritional status without any artificial nutrition, were recruited long after surgery. They received 7-day oral supplementation with citrulline (0.18g/kg/day), or an iso-nitrogenous placebo in a randomized, double-blind, cross-over design with a 13-day wash-out between regimens, and an intravenous 5-h infusion of L-[1-13C]-leucine in the postabsorptive state to assess protein metabolism after each regimen. Plasma citrulline concentration rose 17-fold (25±9 vs. 384±95μmol/L) and plasma arginine 3-fold after oral citrulline supplementation (both p<4×10-6). Supplementation did not alter leucine appearance rate (97±5 vs. 97±5μmolkg-1.h-1; p=0.88), leucine oxidation (14±1 vs. 12±1μmolkg-1.h-1; p=0.22), or non-oxidative leucine disposal (NOLD), an index of whole-body protein synthesis (83±4 vs. 85±5μmolkg-1.h-1; p=0.36), nor insulin or IGF-1 plasma concentrations. In each of the 3 patients with baseline citrulline<20μmol/L, citrulline supplementation increased NOLD. Among the 7 patients with plasma citrulline <30μmol/L, the effect of supplementation on NOLD correlated inversely (r2=0.81) with baseline plasma citrulline concentration. 1) Oral citrulline supplementation enhances citrulline and arginine bioavailability in SBS patients. 2) Oral citrulline supplementation does not have any anabolic effect on whole body protein metabolism in patients with SBS in good nutritional status, in the late phase of intestinal adaptation, and with near-normal baseline citrulline homeostasis. 3) Whether oral citrulline would impact whole body protein anabolism in severely malnourished SBS patients in the early adaptive period, and with baseline plasma citrulline below 20μmol/L, warrants further study. Registered under ClinicalTrials.gov Identifier no. NCT01386034.

Endurance Exercise Attenuates Postprandial Whole-Body Leucine Balance in Trained Men.

Endurance exercise increases indices of small intestinal damage and leucine oxidation, which may attenuate dietary amino acid appearance and postprandial leucine balance during postexercise recovery. Therefore, the purpose of this study was to examine the effect of an acute bout of endurance exercise on postprandial leucine kinetics and net leucine balance. In a crossover design, seven trained young men (age = 25.6 ± 2.3 yr; V˙O2peak = 61.4 ± 2.9 mL·kg·min; mean ± SEM) received a primed constant infusion of L-[1-C]leucine before and after ingesting a mixed macronutrient meal containing 18 g whole egg protein intrinsically labeled with L-[5,5,5-H3]leucine, 17 g fat, and 60 g carbohydrate at rest and after 60 min of treadmill running at 70% V˙O2peak. Plasma intestinal fatty acid binding protein concentrations and leucine oxidation both increased (P < 0.01) to peaks that were ~2.5-fold above baseline values during exercise with a concomitant decrease (P < 0.01) in nonoxidative leucine disposal. Meal ingestion attenuated (P < 0.01) endogenous leucine rates of appearance at rest and after exercise. There were no differences (both, P > 0.05) in dietary leucine appearance rates or in the amount of dietary protein-derived leucine that appeared into circulation over the 5-h postprandial period at rest and after exercise (62% ± 2% and 63% ± 2%, respectively). Leucine balance over the 5-h postprandial period was positive (P < 0.01) in both conditions but was negative (P < 0.01) during the exercise trial after accounting for exercise-induced leucine oxidation. We demonstrate that endurance exercise does not modulate dietary leucine availability from a mixed meal but attenuates postprandial whole-body leucine balance in trained young men.

Dynamics of mTORC1 activation in response to amino acids.

Amino acids are essential activators of mTORC1 via a complex containing RAG GTPases, RAGULATOR and the vacuolar ATPase. Sensing of amino acids causes translocation of mTORC1 to lysosomes, an obligate step for activation. To examine the spatial and temporal dynamics of this translocation, we used live imaging of the mTORC1 component RAPTOR and a cell permeant fluorescent analogue of di-leucine methyl ester. Translocation to lysosomes is a transient event, occurring within 2 min of aa addition and peaking within 5 min. It is temporally coupled with fluorescent leucine appearance in lysosomes and is sustained in comparison to aa stimulation. Sestrin2 and the vacuolar ATPase are negative and positive regulators of mTORC1 activity in our experimental system. Of note, phosphorylation of canonical mTORC1 targets is delayed compared to lysosomal translocation suggesting a dynamic and transient passage of mTORC1 from the lysosomal surface before targetting its substrates elsewhere.

Corticosteroids Increase Protein Breakdown and Loss in Newly Diagnosed Pediatric Crohn Disease

Children with Crohn disease have altered growth and body composition. Previous studies have demonstrated decreased protein breakdown after either corticosteroid or anti-TNF-α therapy. The aim of this study was to evaluate whole body protein metabolism during corticosteroid therapy in children with newly diagnosed Crohn disease. Children with suspected Crohn disease and children with abdominal symptoms not consistent with Crohn disease underwent outpatient metabolic assessment. Patients diagnosed with Crohn disease and prescribed corticosteroid therapy returned in 2 wk for repeat metabolic assessment. Using the stable isotopes [d5] phenylalanine, [1-(13)C] leucine, and [(15)N(2)] urea, protein kinetics were determined in the fasting state. Thirty-one children (18 controls and 13 newly diagnosed with Crohn disease) completed the study. There were no significant differences in protein breakdown or loss between patients with Crohn disease at diagnosis and controls. After corticosteroid therapy in patients with Crohn disease, the rates of appearance of phenylalanine (32%) and leucine (26%) increased significantly, reflecting increased protein breakdown, and the rate of appearance of urea also increased significantly (273%), reflecting increased protein loss. Whole body protein breakdown and loss increased significantly after 2 wk of corticosteroid therapy in children with newly diagnosed Crohn disease, which may have profound effects on body composition.

Oral citrulline does not affect whole body protein metabolism in healthy human volunteers: Results of a prospective, randomized, double-blind, cross-over study

Citrulline increases protein synthesis during refeeding in rodents with short bowel syndrome, aging and malnutrition, and improves nitrogen balance in fed healthy humans. The aim of the current study therefore was to determine whether citrulline had affected protein metabolism in healthy volunteers. In a randomized, double-blind, cross-over study, 12 healthy adults received a 5-h intravenous infusion of L-[1-(13)C]-leucine in the post-absorptive state, after a 7-day oral supplementation with 0.18 g/kg/day citrulline, or an iso-nitrogenous placebo. Treatment order was randomized, treatment periods were separated by 13-day wash out. Leucine appearance rate (Ra) was determined from plasma [1-(13)C]-keto-iso-caproate enrichment and leucine oxidation from expired (13)CO(2), and nitrogen balance was estimated from 6-h urinary urea excretion. Compared with placebo, oral citrulline supplementation increased plasma citrulline, arginine and ornithine concentrations, but failed to affect albumin, transthyretin, free insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance. Citrulline supplementation did not alter leucine Ra, leucine oxidation, nor whole-body protein synthesis. In healthy, well nourished volunteers, oral citrulline increases plasma citrulline and arginine availability but does not affect whole-body protein kinetics in the post-absorptive state.

Protein consumption following aerobic exercise increases whole-body protein turnover in older adults

Research measuring whole-body protein turnover (WBPT) after both exercise and nutrition has generally focused on resistance exercise; however, there is a paucity of data regarding the effect of postaerobic exercise nutrition, especially in older adults. It is not known if postexercise protein feeding has a beneficial effect on protein turnover after low- to moderate-intensity exercise. We investigated whether consuming protein plus carbohydrate (PRO) immediately after an acute bout of aerobic exercise has an additive effect over carbohydrate alone (CHO) on WBPT in older individuals. Twelve healthy older adults (age, 59 ± 4 years) were studied on 2 separate occasions after 1 h of exercise at approximately 50% of maximal rate of oxygen uptake, followed by 4 h of recovery. Immediately following exercise, subjects ingested a CHO (60 g) or an isocaloric PRO beverage (40 g carbohydrate, 20 g whey protein). Whole-body protein metabolism was determined using [1-13C]leucine infusion (60 mg prime; 75 mgh(-1) continuous), and sampling blood and expired breath. Rates of whole-body leucine appearance and oxidation, and nonoxidative leucine disposal during the third and fourth hours of postexercise recovery were higher in the PRO group (2.51 ± 0.55, 0.78 ± 0.37, and 1.71 ± 0.44 micromol kg(-1)·min(-1), respectively) than in the CHO group (1.81 ± 0.27, 0.33 ± 0.14, and 1.47 ± 0.25 micromol kg(-1)·min-1, respectively; p = 0.001). Our results indicate that consumption of a PRO beverage after aerobic exercise increased WBPT to a greater extent than a CHO beverage.

Protein Balance in Nondiabetic Versus Diabetic Patients Undergoing Colon Surgery

Surgical injury provokes a stress response that is thought to be pronounced in patients with diabetes mellitus type 2 (DM2) leading to intensified catabolism. The aim of this study was to compare the effects of perioperative epidural analgesia (EDA) versus patient controlled analgesia (PCA) and amino acid infusion on postoperative metabolism in patients with and without DM2. For this study, 12 nondiabetic patients and 12 diabetic patients undergoing colorectal surgery were randomly assigned to 4 groups (n = 6 per group) receiving either EDA (nondiabetic EDA and diabetic EDA [DEDA group]) or PCA with morphine (nondiabetic PCA and diabetic PCA) for perioperative pain control. Protein and glucose kinetics were measured on the second postoperative day using L-[1-13C]leucine and [6,6-2H2]glucose infusion during a fasted state and a 3-hr fed state with amino acid infusion. The transition from the fasted to fed state suppressed endogenous rate of appearance (Ra) of glucose (P G 0.001) with a distinct effect for the DEDA group (P G 0.001). The Ra of leucine and the endogenous rate of appearance of leucine tended to be lower in the DEDA group(P = 0.056 and P = 0.07). Leucine oxidation was more suppressed in the DEDA group (P = 0.02) and when receiving amino acids(P = 0.001). Diabetic patients achieved a higher protein balance than nondiabetic patients (P = 0.032) and when receiving EDA instead of PCA (P = 0.012) or infusion of amino acids (P = 0.014). A short-term infusion of amino acids reduced protein breakdown, increased protein synthesis, and rendered protein balance positive. This anabolic effect was pronounced in diabetic patients with EDA compared with nondiabetic patients or PCA, respectively, and prevented an undesirable hyperglycemia.

Glucose and protein kinetics in patients undergoing colorectal surgery: perioperative amino acid versus hypocaloric dextrose infusion

Surgical injury provokes a stress response that leads to a catabolic state and, when prolonged, interferes with the postoperative recovery process. This study tests the impact of 2 nutrition support regimens on protein and glucose metabolism as part of an integrated approach in the perioperative period incorporating epidural analgesia in 18 nondiabetic patients undergoing colorectal surgery. To test the hypothesis that parenteral amino acid infusion (amino acid group, n = 9) maintains glucose homeostasis while maintaining normoglycemia and reduces proteolysis compared with infusion of dextrose alone (DEX group, n = 9), glucose and protein kinetics were measured before and on the second day after surgery using a stable isotope tracer technique. Postoperatively, the rate of appearance of glucose was higher ( P < .001) and blood glucose increased more ( P < .001) in the DEX group than in the amino acid group. The postoperative increase in the appearance of leucine from protein breakdown tended to be greater ( P = .077) in the DEX group. We conclude that perioperative infusion of a nutrition support regimen delivering amino acids alone maintains blood glucose homeostasis and normoglycemia and tends to have a suppressive effect on protein breakdown compared with infusion of dextrose alone.

Fibrinogen kinetics and protein turnover in obese non‐diabetic males: effects of insulin

Although hyperfibrinogenemia and insulin resistance are common in obesity and diabetes mellitus, the impact of obesity per se on fibrinogen turnover and the insulin effects on fibrinogen and protein kinetics is unknown. We measured fibrinogen and albumin fractional (FSR) and absolute (ASR) synthesis rates, as well as protein turnover, in non-diabetic, obese and in control male subjects both before and following an euglycemic, euaminoacidemic, hyperinsulinemic clamp, using L-[(2)H(3)]-Leucine isotope infusion. In the obese, basal fibrinogen concentrations was approximately 25% greater (p < 0.035), and fibrinogen pool approximately 45% greater (p < 0.005), than in controls. Both FSR and ASR of fibrinogen were similar to control values. With hyperinsulinemia, although fibrinogen FSR and ASR were not significantly modified with respect to baseline in either group, fibrinogen ASR resulted to be approximately 50% greater in the obese than in controls (p < 0.015). Hyperinsulinemia equally stimulated albumin synthesis and suppressed leucine appearance from endogenous proteolysis in both groups. Amino acid clearance was also similar. In the obese, the insulin-mediated glucose disposal was approximately 50% lower (p < 0.03) than in controls, and it was inversely correlated with fibrinogen ASR during the clamp in both groups (r = - 0.58). In obese, non-diabetic males, post absorptive fibrinogen production is normal. Whole-body amino acid disposal, basal and insulin-responsive protein degradation, and albumin synthesis are also normal. However, the greater fibrinogen ASR in the obese with hyperinsulinemia, and the inverse relationship between insulin sensitivity and clamp fibrinogen production, suggest a role for hyperinsulinemia and/or insulin resistance on fibrinogen production in obesity.

Fibrinogen kinetics and protein turnover in hypertension: Effects of insulin

Background and Aim Hyperfibrinogenemia, a cardiovascular risk factor, is frequent in hypertension and largely unexplained. In this study, we measured fibrinogen production and whole-body protein turnover under both basal and hyperinsulinemic states, in hypertensive [H] and control [C] subjects, using a leucine stable isotope tracer and precursor-product relationships. Methods and results Since hypertension is often a feature of the “metabolic”, insulin resistance syndrome, which in turn affects both fibrinogen kinetics and whole-body protein turnover, we selected hypertensive subjects without the metabolic syndrome. Following basal measurements, an euglycemic, ≈euaminoacidemic, hyperinsulinemic clamp was performed, with plasma insulin raised to 700–900 pmol/L. In H, rates of the fractional and absolute synthesis (FSR and ASR, respectively) of fibrinogen were 30%–40% greater ( p < 0.05 or less) than in C in both states, whereas leucine turnover was normal. Hyperinsulinemia did not modify fibrinogen synthesis in either group with respect to baseline, whereas it suppressed leucine appearance from endogenous proteolysis by ≈40% to same extent in both groups. Amino acid clearance was similar in both the H and C subjects. In H, the insulin-mediated glucose disposal (M) was ≈25% lower, (although insignificantly) than in controls, showing no overall insulin resistance. There was an inverse correlation between M and fibrinogen FSR during the clamp. Conclusions In essential hypertension fibrinogen production is increased, is not further stimulated by insulin, and is inversely related to insulin sensitivity at high-physiological insulin concentrations. Amino acid disposal and basal as well as insulin-responsive protein degradation rates are instead normal.

Effects of 2-hydroxy-4-methylthiobutyrate on portal plasma flow and net portal appearance of amino acids in piglets

To determine whether portal plasma flow (PPF) and net portal appearance of amino acids (AA) could be affected by 2-hydroxy-4-methylthiobutyrate (HMB), six barrows (35-day-old, 8.6+/-1.4 kg), implanted with arterial, portal and mesenteric catheters, were fed a DL-methionine (as the control) or HMB-supplemented diet once hourly and infused intramesenterically with 1% p-amino hippurate. PPF was numerically 9% higher (P=0.09) in HMB-fed pigs than in controls over a 4-6 h period. Compared with controls, pigs fed the HMB diet had increased (P<0.05) net portal balance and/or appearance of leucine, isoleucine, histidine, arginine and alanine, but had decreased (P<0.05) portal appearance of glutamate over a 6-h period. The concentration of acetate in the lumen of the distal small intestine was higher (P=0.01) in HMB-fed pigs than in controls (25.14 vs. 7.64 mmol/kg). mRNA levels for proglucagon and endothelial nitric-oxide synthase (eNOS) in stomach and proximal small intestine, and mRNA levels for GLP-2 receptor (GLP-2R) in stomach were higher (P<0.05) in HMB-fed pigs compared with those in controls. Collectively, HMB supplementation increased concentrations of short-chain fatty acids in intestinal lumen, expression of proglucagon, GLP-2R, and eNOS genes, and net portal absorption of AA. These novel findings from the study with pigs may also have important implications for intestinal nutrition and health in humans.

Epidural Analgesia Enhances the Postoperative Anabolic Effect of Amino Acids in Diabetes Mellitus Type 2 Patients Undergoing Colon Surgery

It has been suggested that diabetes mellitus type 2 amplifies the endocrine-metabolic stress response to surgery, and patients become more catabolic during the postoperative period. The aim of this study, conducted in patients with diabetes mellitus type 2 scheduled to undergo elective colorectal surgery, was to determine whether the anabolic effects of intravenous amino acids are more pronounced when receiving perioperative epidural analgesia compared with patient-controlled analgesia with intravenous morphine. Twelve patients were randomly assigned to receive either epidural analgesia or patient-controlled analgesia with intravenous morphine for perioperative pain control. Protein and glucose kinetics were measured before surgery and on the second postoperative day using L-[1-C]leucine and [6,6H2]glucose infusion during a fasted and a fed (amino acid infusion) state. Preoperative parameters for glucose and protein kinetics were comparable in the fasted state for both groups. Postoperative amino acid infusion increased glucose concentration slightly (P = 0.124) and suppressed the endogenous rate of appearance of glucose (P < 0.0001) and glucose clearance (P < 0.0001) regardless of analgesia technique. The rate of appearance of leucine (P = 0.002), leucine oxidation (P < 0.0001), and protein synthesis (P = 0.026) increased, whereas net protein breakdown was decreased (P = 0.002), leading to a positive protein balance (P < 0.0001) in both groups. The increase in protein balance was greater in the epidural group compared with the patient-controlled analgesia group (P = 0.027). Diabetic patients receiving an amino acid infusion after surgery achieved a positive protein balance without hyperglycemia. This anabolic effect was greater in patients receiving epidural analgesia compared with patient-controlled analgesia with intravenous morphine.

Impact of Growth Hormone and Dehydroepiandrosterone on Protein Metabolism in Glucocorticoid-Treated Patients

Chronic pharmacological glucocorticoid (GC) use causes substantial morbidity from protein wasting. GH and androgens are anabolic agents that may potentially reverse GC-induced protein loss. Our objective was to assess the effect of GH and dehydroepiandrosterone (DHEA) on protein metabolism in subjects on long-term GC therapy. This was an open, stepwise GH dose-finding study (study 1), followed by a randomized cross-over intervention study (study 2). The studies were performed at a clinical research facility. In study 1, six subjects (age 69+/-4 yr) treated with long-term (>6 months) GCs (prednisone dose 8.3+/-0.8 mg/d) were studied before and after two sequential GH doses (0.8 and 1.6 mg/d) for 2 wk each. In study 2, 10 women (age 71+/-3 yr) treated with long-term GCs (prednisone dose 5.4+/-0.5 mg/d) were studied at baseline and after 2-wk treatment with GH 0.8 mg/d, DHEA 50 mg/d, or GH and DHEA (combination treatment). Changes in whole body protein metabolism were assessed using a 3-h primed constant infusion of 1-[13C]leucine, from which rates of leucine appearance, leucine oxidation, and leucine incorporation into protein were estimated. In study 1, GH 0.8 and 1.6 mg/d significantly reduced leucine oxidation by 19% (P=0.03) and 31% (P=0.02), and increased leucine incorporation into protein by 10% (P=0.13) and 19% (P=0.04), respectively. The lower GH dose did not cause hyperglycemia, whereas GH 1.6 mg/d resulted in fasting hyperglycemia in two of six subjects. In study 2, DHEA did not significantly change leucine metabolism alone or when combined with GH. Blood glucose was not affected by DHEA. GH, at a modest supraphysiological dose of 0.8 mg/d, induces protein anabolism in chronic GC users without causing diabetes. DHEA 50 mg/d does not enhance the effect of GH. GH may safely prevent or reverse protein loss induced by chronic GC therapy.

Impact of Acute and Chronic Low-Dose Glucocorticoids on Protein Metabolism

High-dose glucocorticoids cause acute protein loss by increasing protein breakdown and oxidation. Whether lower glucocorticoid doses, typical of therapeutic use, induce sustained catabolism has not been studied. Our objective was to assess the effect of acute and chronic therapeutic glucocorticoid doses on protein metabolism. We conducted an open longitudinal and a cross-sectional study at a clinical research facility. Ten healthy subjects were studied before and after a short course of prednisolone (5 and 10 mg/d sequentially for 7 d each). Twelve subjects with inactive polymyalgia rheumatica receiving chronic (>12 months) prednisone (mean = 5.0 +/- 0.8 mg/d) were compared with 12 age- and gender-matched normal subjects. Whole-body protein metabolism was assessed using a 3-h primed constant infusion of 1-[(13)C]leucine, from which rates of leucine appearance (leucine Ra, an index of protein breakdown), leucine oxidation (Lox, index of protein oxidation) and leucine incorporation into protein (LIP, index of protein synthesis) were estimated. Prednisolone induced an acute significant increase in Lox (P = 0.008) and a fall in LIP (P = 0.08) but did not affect leucine Ra. There was no significant difference between the effects of the 5- and 10-mg prednisolone doses on leucine metabolism. In subjects receiving chronic prednisone therapy, leucine Ra, Lox, and LIP were not significantly different from normal subjects. Glucocorticoids stimulate protein oxidation after acute but not chronic administration. This time-related change suggests that glucocorticoid-induced stimulation of protein oxidation does not persist but that a metabolic adaptation occurs to limit protein loss.

Pre-operative nutritional status does not alter the metabolic response to major gastrointestinal surgery in patients with oesophageal cancer

Malnutrition is associated with an increased incidence of perioperative morbidity and mortality. To evaluate the effect of malnutrition on the metabolic and inflammatory response to surgery in patients with oesophageal cancer, we studied the effects of oesophagectomy in six patients with major (13.9 (se 1.3) %) weight loss and five patients with minor (0.7 (se 0.6) %) weight loss in the 6 months before to surgery. Rates of appearance (Ra) of glucose, glycerol, leucine and urea were determined by stable isotopically labelled tracer infusion before and after surgery. C-reactive protein was measured as an inflammation marker. BMI was lower in the patients with major weight loss than those with minor weight loss (20.3 (se 0.7) and 24.9 (se 1.5) kg/m2, P = 0.02). With the exception of greater glucose Ra in the major weight loss than minor weight loss subjects (11.1 (se 0.3) v. 9.5 (se 0.3) mumol/kg per min, P = 0.01), there were no differences in substrate kinetics before surgery between groups. Surgery increased glucose Ra, leucine Ra and urea Ra by 41, 24 and 58 %, respectively, in the total group. Changes in substrate kinetics in response to surgery were not different between patients with major and minor weight loss. Surgery increased C-reactive protein concentrations to a comparable extent in both groups. In conclusion, major upper gastrointestinal tract surgery in patients with oesophageal cancer elicits a catabolic response, characterized by increased inflammation, glucose production and protein breakdown. However, this catabolic response does not seem to be influenced by pre-operative nutritional status.

A Randomized Controlled Trial of the Anticatabolic Effect of Epidural Analgesia and Hypocaloric Glucose

The goal of the present study was to investigate whether epidural analgesia exerts a protein-sparing effect after colorectal surgery in the presence of hypocaloric glucose supply initiated with surgical skin incision. We randomly allocated 10 patients to receive general anesthesia combined with epidural anesthesia with bupivacaine, followed by epidural analgesia using bupivacaine/fentanyl, and 10 patients to receive general anesthesia, followed by patient-controlled analgesia with intravenous morphine. All patients received a 48-hour infusion of glucose 10% from surgical skin incision until the second day after surgery. The glucose infusion rate provided 50% of the patient's resting energy expenditure. Kinetics of protein and glucose metabolism were assessed by a stable-isotope tracer technique (L-[1-(13)C]leucine and [6,6-(2)H(2)]glucose). The rate of appearance of leucine increased in the intravenous-analgesia group (112 +/- 29 to 130 +/- 25 micromol/kg/h) 2 days after surgery, and this increase was more pronounced than in the epidural analgesia group (preoperative 120 +/- 24, postoperative 123 +/- 22 micromol/kg/h, P < .05). Leucine oxidation rate increased in the intravenous analgesia group from 17 +/- 8 to 23 +/- 8 micromol/kg/h and in the epidural group from 17 +/- 6 to 19 +/- 7 micromol/kg/h without the difference between the groups reaching statistical significance (P = .067). Nonoxidative leucine disposal remained unaltered in both groups. No differences in glucose metabolism were seen between the groups. Epidural analgesia inhibits the increase in whole-body protein breakdown in patients receiving perioperative hypocaloric glucose infusion initiated with surgical skin incision. However, oxidative protein loss, protein synthesis, and glucose metabolism are not affected by epidural analgesia.

Dynamics of albumin synthesis after major rectal operation

Major abdominal operations were found to be associated with long-lasting metabolic changes, such as accelerated release of stress hormones and carbohydrate turnover. It is unknown currently whether acute changes of hepatic protein metabolism persist in a similar way. We wanted to determine the long-term dynamics of albumin synthesis and its relationship to whole body protein breakdown and albumin concentration after major rectal operations. We used stable isotope tracer techniques to determine albumin synthesis and whole body protein breakdown (rate of appearance of leucine, Ra) in postoperative patients about 1 week after low anterior rectal resection and also during convalescence (about 4 months after operation), and in healthy controls. Consecutive blood sampling was carried out during continuous isotope infusion (1-[(13)C]-leucine, 0.16 micromol/kg min). Serum albumin concentrations were close to the lower normal limit in patients early after operation but were comparable to controls in convalescent patients. Simultaneously, albumin synthesis was increased in the early postoperative phase (0.53 +/- 0.0.5%/h) compared with convalescent patients (0.32 +/- 0.04) and controls (0.28 +/- 0.04) (P < .01 each). A significant inverse correlation could be found between plasma albumin concentration and corresponding rates of albumin synthesis. Early after operation patients showed an increased leucine Ra (3.25 +/- 0.23 micromol/kg min) that was greater than that of convalescent patients (2.37 +/- 0.06 micromol/kg min, P < .05). Leucine Ra in both patient groups were greater than the rates in controls (2.01 +/- 0.07 micromol/kg min, P < .01) Albumin synthesis correlated weakly with whole body protein breakdown rate. Albumin synthesis and total body protein breakdown are increased after major abdominal operation, but albumin synthesis returns to control values only during convalescence. Hypoalbuminemia after rectal operations may be associated with high rates of albumin synthesis and is, therefore, not necessarily an indicator of insufficient hepatic function or poor nutritional status in that particular situation.

Protein metabolism in glucocorticoid excess: study in Cushing's syndrome and the effect of treatment

How protein metabolism is perturbed during chronic glucocorticoid excess is poorly understood. The aims were to investigate the impact of chronic glucocorticoid excess and restoration of eucortisolemia in Cushing's syndrome (CS) on whole body protein metabolism. Eighteen subjects with CS and 18 normal subjects (NS) underwent assessment of body composition using DEXA and whole body protein turnover with a 3-h constant infusion of l-[(13)C]leucine, allowing calculation of rates of leucine appearance (leucine R(a)), leucine oxidation (L(ox)), and leucine incorporation into protein (LIP). Ten subjects with CS were restudied after restoration of eucortisolemia. Percentage FM was greater (43.9 +/- 1.6 vs. 33.8 +/- 2.4%, P = 0.002) and LBM lower (52.7 +/- 1.6 vs. 62.1 +/- 2.3%, P = 0.002) in CS. LBM was significantly correlated (r(2) > 0.44, P < 0.005) to leuceine R(a), L(ox), and LIP in both groups. After correcting for LBM, leucine R(a) (133 +/- 5 vs. 116 +/- 5 micromol/min, P = 0.02) and L(ox) (29 +/- 1 vs. 24 +/- 1 micromol/min, P = 0.01) were greater in CS. FM significantly correlated (r(2) = 0.23, P < 0.05) with leucine R(a) and LIP, but not L(ox) in CS. In multiple regression, LBM was an independent determinant of all three indexes of leucine turnover, FM of leucine R(a), and LIP and CS of L(ox). Following restoration of eucortisolemia, L(ox) was reduced (Delta-7.5 +/- 2.6 micromol/min, P = 0.02) and LIP increased (Delta+15.2 +/- 6.2 micromol/min, P = 0.04). In summary, whole body protein metabolism in CS is influenced by changes in body composition and glucocorticoid excess per se, which increases protein oxidation. Enhanced protein oxidation is a likely explanation for the reduced protein mass in CS. Successful treatment of CS reduces protein oxidation and increases protein synthesis to prevent ongoing protein loss.

Protein Metabolism in Acromegaly: Differential Effects of Short- and Long-Term Treatment

GH acutely increases body protein by stimulating protein synthesis and reducing protein oxidation. The objective of the study was to determine whether these changes in protein metabolism are sustained in long-term GH excess and reversed by correction. We conducted a cross-sectional study in 16 acromegalic and 18 normal subjects and a longitudinal study in which acromegalic subjects were studied before and after short-term (n=8) or long-term (n=10) treatment. The study was conducted at a clinical research center. Whole-body rates of leucine appearance (leucine Ra; an index of protein breakdown), leucine oxidation, and nonoxidative leucine disposal (NOLD; an index of protein synthesis) estimated using infusion of 1-[13C] leucine were measured. Leucine Ra and NOLD were greater (P<0.01) in acromegalic compared with normal subjects, whereas leucine oxidation did not differ. Leucine oxidation increased significantly (P<0.05) after short-term treatment but returned to baseline after long-term treatment. Both leucine Ra and NOLD decreased significantly (P<0.05) after short- and long-term treatment. Adjustment for body composition did not affect results. In acromegalic subjects, protein breakdown and synthesis are increased, whereas protein oxidation does not differ from normal subjects. Protein oxidation increases transiently, whereas protein breakdown and synthesis are stably reduced after treatment. Because protein oxidation represents irreversible loss, we conclude that the normal state of protein oxidation found in acromegaly and after long-term treatment represents metabolic adaptation, which maintains protein mass at a steady state after stable changes in GH status.

Intraoperative Infusion of Amino Acids Induces Anabolism Independent of the Type of Anesthesia

The infusion of dextrose in patients receiving epidural and light general anesthesia or general anesthesia alone failed to achieve a positive protein balance. We sought to verify the hypothesis that nutritional supplementation with i.v. amino acids induced a greater protein balance in patients receiving epidural blockade compared with those receiving general anesthesia. Sixteen patients were randomly assigned to receive either general anesthesia with desflurane (control group) or general anesthesia combined with epidural analgesia (EDA group). A primed constant infusion of stable isotope tracers L-[1-(13)C]leucine and [6,6-(2)H2]glucose was started after a 32-h fast before surgery, (3 h of fasted state), and continued for 3 h during surgery during which amino acids were infused i.v. (fed state). Compared with the fasted state, the endogenous rate of appearance of leucine decreased to a similar extent in both groups, and protein synthesis increased, with no difference between the two groups. Leucine oxidation did not change in either group. After amino acids infusion, endogenous glucose production remained unchanged and glucose clearance decreased in both groups. Blood glucose, plasma cortisol, serum insulin, and glucagon concentrations increased to the same extent in both groups. Epidural anesthesia provided no additional benefit beyond the anabolism obtained with amino acids.