Decrease in human quadriceps muscle protein turnover consequent upon leg immobilization

Quadriceps muscle protein turnover was assessed in the post-absorptive state in six men immediately after the end of unilateral leg immobilization (37 +/- 4 days) in a plaster cast after tibial fracture. A primed-constant intravenous infusion of L-[1-13C]leucine was administered over 7 h. Quadriceps needle biopsies, taken bilaterally at the end of the infusion, were analysed for muscle protein leucine enrichment with 13C. Quadriceps muscle protein synthetic rate, calculated from the fractional incorporation of [13C]leucine into protein compared with the average enrichment of blood alpha-ketoisocaproate, was 0.046 +/- 0.012%/h in the uninjured leg, but was only 0.034 +/- 0.007%/h in the quadriceps of the previously fractured leg (P less than 0.05, means +/- SD). Muscle RNA activity (i.e. protein synthetic rate per RNA) fell from 0.27 +/- 0.08 microgram of protein synthesized h-1 microgram-1 of RNA in the control leg to 0.14 +/- 0.03 microgram of protein synthesized h-1 microgram-1 of RNA in the immobilized leg (P less than 0.02). Immobilization was associated with a significant atrophy of type I muscle fibres (mean diameter 69.5 +/- 21 microns immobilized, 81.1 +/- 18 microns control, P less than 0.05), but no significant change occurred in type II fibre diameter. Mean quadriceps fibre volume calculated from the values for fibre diameter and percentage of each fibre type, was smaller in the injured leg by 10.6%; this value was near to the calculated difference in muscle thigh volume (calculated from thigh circumference and skin-fold thickness) which was less by 8.3%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of adrenaline infusion on fatty acid and glucose turnover in lean and obese human subjects in the post-absorptive and fed states.

1. Energy expenditure, plasma glucose and palmitate kinetics and leg glycerol release were determined simultaneously both before and during adrenaline infusion in lean and obese human subjects. Seven lean subjects (mean 96.5% of ideal body weight) were studied in the post-absorptive state and also during mixed nutrient liquid feeding, eight obese subjects (mean 165% of ideal body weight) were studied in the post-absorptive state and six obese subjects (mean 174% of ideal body weight) were studied during feeding. 2. Resting energy expenditure was higher in the obese subjects, but the thermic response to adrenaline, both in absolute and percentage terms, was similar in lean and obese subjects. Plasma adrenaline concentrations attained (3 nmol/l) were comparable in all groups and the infusion had no differential effects on the plasma insulin concentration. Before adrenaline infusion the plasma glucose flux was higher in the obese than in the lean subjects in the fed state only (45.8 +/- 3.8 versus 36.6 +/- 1.0 mmol/h, P less than 0.05); it increased to the same extent in both groups with the adrenaline infusion. 3. Before the adrenaline infusion plasma palmitate flux was higher in the obese than in the lean subjects (by 51%, P less than 0.01, in the post-absorptive state and by 78%, P less than 0.05, in the fed state). However, there was no significant change during adrenaline infusion in the obese subjects (from 13.5 +/- 1.00 to 15.0 +/- 1.84 mmol/h, not significant, in the post-absorptive state and from 14.4 +/- 2.13 to 15.7 +/- 1.74 mmol/h, not significant, in the fed state), whereas there were increases in the lean subjects (from 8.93 +/- 1.10 to 11.2 +/- 1.19 mmol/h, P less than 0.05, in the post-absorptive state, and from 8.06 +/- 1.19 to 9.86 +/- 0.93 mmol/h, P less than 0.05, in the fed state). 4. Before adrenaline infusion the palmitate oxidation rate was also higher in the obese than in the lean subjects (1.86 +/- 0.14 versus 1.22 +/- 0.09 mmol/h, P less than 0.01, in the post-absorptive state and 1.73 +/- 0.25 versus 1.12 +/- 0.12 mmol/h, P less than 0.05, in the fed state). However, in response to adrenaline the fractional oxidation rate (% of flux) increased less in the obese than in the lean subjects, especially in the post-absorptive state (from 13.8 +/- 1.02 to 14.9 +/- 1.39%, not significant, versus from 13.7 +/- 0.98 to 19.3 +/- 1.92%, P less than 0.05). These effects were independent of feeding.(ABSTRACT TRUNCATED AT 400 WORDS)     

Skeletal muscle and whole body protein turnover in thyroid disease

The effects of disturbances of thyroid hormone secretion on leg and whole body amino acid and protein metabolism have been investigated in seven patients with untreated thyrotoxicosis and eight patients with untreated hypothyroidism; the results were compared to those obtained in 11 normal control subjects. After treatment, the patients were restudied. Arterio-venous exchanges of tyrosine and 3-methylhistidine across leg tissue in the post-absorptive state were used as indices of net protein balance and myofibrillar protein breakdown, respectively. Whole body protein turnover was measured using stable isotope labelling techniques with 1-[1-13C] leucine. Efflux of tyrosine from leg tissues was six-fold greater in patients with untreated thyrotoxicosis than in normal control subjects (-19.39 +/- 2.21 vs. -4.20 +/- 0.31 nmol 100 g-1 leg tissue min-1, P less than 0.005, mean +/- SEM), but 3-methyl-histidine efflux was not significantly different (-0.11 +/- 0.03 nmol 100 g-1 leg tissue min-1 vs. 0.14 +/- 0.02 nmol 100 g-1 leg tissue min-1). After treatment, when the thyrotoxic patients became euthyroid, tyrosine efflux was normalized (at -4.94 +/- 0.84 nmol 100 g-1 leg tissue min-1) and 3-methylhistidine efflux was unchanged. In hypothyroid patients, neither tyrosine nor 3-methylhistidine effluxes were significantly different from those in normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of muscle glutamine formation in hypercatabolic patients.

Glutamine is synthesized primarily in skeletal muscle, and enables transfer of nitrogen to the liver, as well as serving other functions. There is increasing evidence for beneficial clinical effects of glutamine supplementation in critically ill patients. However, the response of endogenous glutamine formation to severe stress is poorly understood. The rates of net protein balance, leucine oxidative decarboxylation, and alanine and glutamine synthesis de novo were determined in leg skeletal muscle of 20 severely burned patients and 19 normal controls in the post-absorptive state. Patients were studied at 14+/-5 days post-burn, and their mean burn size was 66+/-18% of total body surface area. Methods were based on the leg arteriovenous balance technique in combination with biopsies of the vastus lateralis muscle. In the post-absorptive state, patients with severe burns, as compared with healthy control subjects, exhibited accelerated muscle loss (+150%) (i.e. proteolysis minus synthesis) and leucine oxidative decarboxylation (+117%), and depletion of the intramuscular free glutamine pool (-63%). The average rate of glutamine synthesis de novo was decreased by 48%, whereas net alanine synthesis de novo was increased by 174%, in skeletal muscle of burned patients. In conclusion, in severely hypercatabolic burned patients, muscle glutamine formation was suppressed, whereas alanine was the major vehicle for inter-organ nitrogen transport. These changes account for a decreased glutamine availability during prolonged severe stress.     

Muscle protein synthesis in patients with rheumatoid arthritis: effect of chronic corticosteroid therapy on prostaglandin F2α availability

Using stable-isotope techniques, we measured rates of quadriceps muscle protein synthesis in twelve women with sero-positive rheumatoid arthritis. The results were compared to those from the normal limb of seven women with unilateral osteoarthritis of the knee. Six patients had never received corticosteroid immuno-suppression, but the other six had taken an average of 8 mg Prednisolone per day for 9 years. Quadriceps atrophy was present in both sets of patients with rheumatoid arthritis (normal legs 444 +/- 182, rheumatoid 190 +/- 40, rheumatoid + steroid 300 +/- 110 micrograms protein/micrograms DNA, means +/- SD, both P less than 0.001). Muscle protein synthesis, calculated by comparing the incorporation of 13C-leucine into biopsy samples taken after an 8 h L-[1-13C] leucine infusion with the time averaged enrichment of blood alpha-ketoisocaproate, was 0.056 +/- 0.005% h-1 in the patients not receiving steroids compared with 0.050 +/- 0.02% h-1 in normals (P greater than 0.05) indicating that muscular atrophy was primarily due to an increase in rate of muscle protein breakdown. Intra-muscular PGE2 concentration was increased in these patients (rheumatoid 0.12 +/- 0.06 ng mg-1 tissue, normals 0.06 +/- 0.03 ng mg-1 tissue, P less than 0.05). Patients taking corticosteroids had a markedly depressed rate of muscle protein synthesis (0.035 +/- 0.008% h-1, P less than 0.05) and reduced intra-muscular PGF 2 alpha concentration (P less than 0.01). We conclude that steroid therapy significantly influences the mechanism of skeletal muscle atrophy in patients with rheumatoid arthritis.     

Effects of therapeutic percutaneous electrical stimulation of atrophic human quadriceps on muscle composition, protein synthesis and contractile properties

The effects of percutaneous electrical stimulation (70 V, 300 microseconds pulses at 30 Hz) on muscle composition and rate of protein synthesis were studied in seven patients with quadriceps atrophy secondary to unilateral osteoarthritis of the knee (stimulated group). Quadriceps were stimulated on the affected side for 1 h per day. The results were compared to those from seven patients who did not use a muscle stimulator (control group), in whom muscle biopsy at surgery provided evidence of wasting of tissue protein on the side of osteoarthritis (normal leg 608 +/- 266 micrograms protein micrograms-1 DNA, affected leg 256 +/- 100 micrograms protein micrograms-1 DNA, means +/- SD, P less than 0.05; type I fibre diameters: normal 53.2 +/- 6.7 microns, affected 43.8 +/- 4.0 microns, P less than 0.05). In patients who had received stimulation there was no residual difference between the legs in either muscle protein concentration (normal 411 +/- 168 micrograms protein micrograms-1 DNA, affected 373 +/- 112 micrograms protein micrograms-1 DNA) or fibre diameter (type I diameters: normal 56.1 +/- 7.8 microns, affected 58.0 +/- 10.7 microns). Stimulation did not influence the ratios of muscle force elicited by acute stimulation at 20 and 50 Hz (normal 75 +/- 15%, affected 79 +/- 15%), or rates of muscle relaxation (percentage losses of tetanic force 10 ms-1: normal 7.66 +/- 1.2%, affected 8.67 +/- 2.2%).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of amino acid infusion on leg protein turnover assessed by L-[15N]phenylalanine and L-[1-13C]leucine exchange

A stable isotope technique depending on the use of [15N]phenylalanine and [1-13C]leucine to assess exchange was utilized to measure the components of protein turnover of the human leg and the effects of amino acid infusion. Eight healthy subjects (28.5 +/- 2.5 years) were studied when post-absorptive in the basal state and again during infusion of a mixed amino acid solution (55 g l-1, 1.52 ml kg-1 h-1). During the basal period leucine oxidation by the leg was 4.4 +/- 2.0 nmol 100 g-1 min-1 and this increased threefold during amino acid infusion (13.6 +/- 3.1 nmol 100 g-1 min-1, mean +/- SEM, P = 0.003). Amino acid infusion abolished the net negative balance between incorporation of leucine into, and release from, protein (basal, -31.8 +/- 5.8; during infusion, +3.1 +/- 7.1 nmol 100 g-1 P = 0.001). Phenylalanine exchange showed a similar pattern (basal, -13.7 +/- 1.8; during infusion, -0.8 +/- 3.0 nmol 100 g-1 min-1, P = 0.003). Basal entry of leucine into leg protein (i.e. protein synthesis) was 70.0 +/- 10.8 nmol 100 g-1 min-1 and this increased during amino acid infusion to 87.3 +/- 14.1 nmol 100 g-1 min-1 (P = 0.11). Phenylalanine entry to protein also increased with amino acid infusion (29.1 +/- 4.5 vs. 38.3 +/- 5.8 nmol 100 g-1 min-1, P = 0.09). Release from protein of leucine (101.8 +/- 9.1 vs. 84.2 +/- 9.1 nmol 100 g-1 min-1, P = 0.21) and of phenylalanine (42.8 +/- 4.2 vs. 39.1 +/- 4.2 nmol 100 g-1 min-1, P = 0.50) was unchanged by amino acid infusion. The results suggest that, in the post-absorptive state in man, infusion of mixed amino acids, without additional energy substrates; reverses negative amino acid balance by a mechanism which includes stimulation of muscle protein synthesis but which does not alter protein breakdown. Interpretation of the results obtained concurrently on whole-body protein turnover suggests that the increase in muscle protein synthesis contributes substantially to the whole-body increase, but the fall in whole-body breakdown with exogenous amino acids is independent of changes in muscle.     

Relationship between turnover rate and oxidation rate of alanine in the post-absorptive state and during parenteral nutrition before and after surgery

The influence of total parenteral nutrition and stomach resection on alanine turnover rate and alanine oxidation rate was measured in ten patients after single injection of U-14 C-alanine. Sequential studies were done in three patients. During parenteral nutrition alanine turnover was significantly higher than in the post-abortive state (14.75 +/- 2.56 mumol kg-1 min-1 and 8.48 +/- 1.88 mumol kg-1 min-1, respectively; P less than 0.01, mean +/- s.d.). Surgery had no additional significant influence on alanine turnover. In the post-absorptive state 4.71 +/- 0.71 mumol kg-1 min-1 was oxidized, during parenteral feeding before surgery 7.93 +/- 1.93 mumol kg-1 min-1 (P less than 0.01 v. post-absorptive state), and during parenteral feeding after surgery 7.67 +/- 1.67 mumol kg-1 min-1. The percentages of alanine turnover used for oxidation in the post-absorptive state and during parenteral feeding before and after surgery were 57 +/- 11%, 54 +/- 7% and 45 +/- 11%, respectively (no significant differences). It is concluded that the degree of alanine oxidation seems to be directed by the degree of alanine turnover. A discussion about differences in alanine oxidation under different circumstances must therefore include a discussion about changes in alanine turnover.     

Effect of eating on plasma radical-trapping antioxidant activity (TRAP) in patients with cirrhosis

OBJECTIVES: To ascertain the effects of eating on plasma antioxidant capacity in patients with liver disease. DESIGN AND METHODS: Eighteen cirrhotic patients were compared to 18 age and sex-matched controls. TRAP was measured by a fluorometric assay after a 12 h fast, and 60, 120, and 180 min after the study participants had taken a drink formula food. RESULTS: In the fasting state, TRAP was higher in patients with alcoholic cirrhosis (847+/-39 micromol/L, mean +/- SEM) in comparison to patients with viral cirrhosis (653+/-41) and to controls (758+/-26) (p<0.005). In cirrhotic patients, TRAP did not change in the post-absorptive state. In controls, TRAP decreased progressively, to a value of 719+/-21 (p<0.02), and the AUC of the delta-values of TRAP and of plasma insulin showed an inverse correlation (r = -0.52, p<0.05). CONCLUSIONS: In normal subjects, but not in cirrhotics, TRAP decreases in the post-absorptive state, probably in relationship with the activation of metabolic pathways.     

Small-intestinal mucosal protein synthesis and whole-body protein turnover in alcoholic liver disease

We used stable-isotope-labelled amino acids to measure the effects of alcoholic liver disease (ALD) on whole-body protein turnover and small-intestinal mucosal protein synthesis. Groups comprising eight patients with ALD and eight healthy control subjects were studied. They received primed, continuous intravenous infusions of L-[1-(13)C]leucine after an overnight fast; after 4 h, duodenal biopsies were obtained via endoscopy. Protein synthesis was calculated from protein labelling relative to intracellular leucine enrichment. Rates of duodenal mucosal protein synthesis were 2. 58+/-0.32%.h(-1) (mean+/-S.D.) in the normal subjects and 2.04+/-0. 18%.h(-1) in the ALD patients (P<0.003), despite the fact that the protein synthetic capacity (microgram of RNA/mg of protein) was higher in ALD patients (160+/-14 compared with 137+/-6 microgram/mg; P<0.003). The mucosal cell size (protein/DNA ratio) was lower in ALD patients (9.23+/-0.91 compared with 13+/-2.2 microgram/mg; P<0.002). Although the mean rates of whole-body protein turnover were not significantly different between the two groups (204+/-18 and 196+/-44 micromol leucine.h(-1).kg(-1) for ALD and control subjects respectively), there was, in the ALD patients, an inverse relationship between the rate of small-intestinal mucosal protein synthesis and the severity of ALD; furthermore, there was a direct relationship between the rate of whole-body protein turnover and the severity of ALD. Thus there was an inverse relationship between the rate of small-intestinal mucosal protein synthesis and the rate of whole-body protein turnover in ALD patients, which was not seen in the normal subjects.     

Decreased insulin sensitivity of forearm muscle in myotonic dystrophy.

Previous studies of patients with myotonic dystrophy have demonstrated hyperinsulinism after glucose loading. This hyperinsulinism has been attributed by some investigators to tissue insulin resistance. We have directly studied insulin sensitivity of forearm muscle in patients having such hyperinsulinism. The effect of an intrabrachial arterial insulin infusion (100 mu U/kg per min) on glucose uptake was determined in six cases of myotonic dystrophy, six normal subjects, and in seven disease control subjects with myotonia or wasting from other disorders. There was no significant difference in insulin tolerance comparing myotonic dystrophy patients to the normal and disease control groups. Glucose tolerance and basal insulin levels were normal in the myotonic dystrophy patients, but hyperinsulinism occurred after glucose ingestion. After 25 min of intra-arterial insulin, the mean peak muscle glucose uptake in myotonic dystrophy was 2.54 +/- 0.54 mu mol/min per 100 ml forearm compared to 5.24 +/- 0.86 mu mol/min per 100 ml for disease controls (P is less than 0.05). Myotonic dystrophy patients showed a peak glucose uptake increment of only 2.6 +/- 0.2-fold over basal contrasted with the disease control value of 6.5 +/- 1.0-fold (P is less than 0.02) and the normal control value of 8.8 +/- 1.1-fold (P is less than 0.01). Thus, there was an absolute as well as a relative decrease in muscle insulin sensitivity in myotonic dystrophy patients compared to both control groups. The peak increments in arterio-superficial venous glucose concentration differences after insulin infusion were not significantly different comparing myotonic dystrophy and control groups. These data suggest that in myotonic dystrophy, there is insulin insensitivity of skeletal muscle.     

Peak flow and peak cough flow in the evaluation of expiratory muscle weakness and bulbar impairment in patients with neuromuscular disease

OBJECTIVE: To study the expiratory muscle force and the ability to cough estimated by the peak expiratory flow and peak cough flow in patients with Duchenne muscular dystrophy and amyotrophic lateral sclerosis. DESIGN: A total of 27 patients with amyotrophic lateral sclerosis and 52 patients with Duchenne muscular dystrophy were studied. From the group of 144 normal subjects of this laboratory, we selected 38 for comparison. RESULTS: The maximal inspiratory pressure in patients with Duchenne muscular dystrophy and amyotrophic lateral sclerosis was 64.5 +/- 24.7% and 37.8 +/- 21.8%, respectively, and maximal expiratory pressure was 64.2 +/- 32.5% and 37.7 +/- 21.6%, respectively. Patient groups showed a significant lower peak expiratory flow than normal subjects. Higher peak cough flow than peak expiratory flow was found in all groups. The peak cough flow-peak expiratory flow difference was 46 +/- 18% in normal subjects, 43 +/- 23% in patients with Duchenne muscular dystrophy, and 11 +/- 17% in patients with amyotrophic lateral sclerosis. The peak expiratory flow and peak cough flow were not different in bulbar onset amyotrophic lateral sclerosis. In patient groups, the dynamic and static behavior correlated positively. CONCLUSIONS: These results suggest that peak cough flow-peak expiratory flow is useful to monitor expiratory muscle weakness and bulbar involvement and to assess its evolution in these patients.     

Teicoplanin pharmacokinetics in patients undergoing continuous ambulatory peritoneal dialysis after intravenous and intraperitoneal dosing.

The pharmacokinetics of teicoplanin after single 6-mg/kg intravenous and intraperitoneal doses were studied in five noninfected patients undergoing continuous ambulatory peritoneal dialysis. Biological samples were assayed for teicoplanin content by a microbiological assay technique. Terminal disposition half-life (266.4 +/- 51.9 h [mean +/- standard error of the mean]) was prolonged and total body clearance (0.040 +/- 0.004 ml/min per kg) was reduced compared with values previously reported in subjects with normal renal function. The volume of distribution at steady state (1.15 +/- 0.19 liters/kg) was higher than values previously reported in subjects with normal renal function (0.56 to 0.72 liter/kg). Peritoneal dialysis clearance (0.007 +/- 0.001 ml/min per kg) accounted for only 16.1% of total body clearance. The absolute systemic bioavailability of teicoplanin after intraperitoneal administration was 81.5 +/- 10.7%.     

Muscle and bone in paraplegic patients, and the effect of functional electrical stimulation

1. Four paraplegic men volunteered for an exercise programme in which their paralysed quadriceps muscles were stimulated by means of computer-regulated electrical impulses applied through external electrodes. The first exercise regimen consisted of leg raising against a graded load, and during the second regimen exercise took the form of cycling on a modified bicycle ergometer. Each subject exercised five times weekly for 10 weeks during the first regimen and 32 weeks during the second regimen. 2. Whole-body protein turnover determined by L-[1-13C]leucine during feeding remained constant during both exercise regimens, when expressed either in terms of body weight or fat-free mass derived from measurements of total body potassium. 3. Quadriceps muscle protein synthetic rate increased during the study, from 0.0712 to 0.0985%/h (P less than 0.05), as did quadriceps muscle area assessed by computed tomography. 4. Bone mineral content for lumbar vertebrae was normal in all four patients, but for the femoral mid-shaft bone mineral content averaged only 66% of normal for three of the patients. Trabecular bone density in the distal tibia ranged from normal to 2% of normal for the men with the shortest and longest periods of disability, respectively. No changes in bone mineral content or bone density occurred during the exercise period.     

Overexpression of Glut4 protein in muscle increases basal and insulin-stimulated whole body glucose disposal in conscious mice.

The effect of increased Glut4 protein expression in muscle and fat on the whole body glucose metabolism has been evaluated by the euglycemic hyperinsulinemic clamp technique in conscious mice. Fed and fasting plasma glucose concentrations were 172 +/- 7 and 78 +/- 7 mg/dl, respectively, in transgenic mice, and were significantly lower than that of nontransgenic littermates (208 +/- 5 mg/dl in fed; 102 +/- 5 mg/dl in fasting state). Plasma lactate concentrations were higher in transgenic mice, (6.5 +/- 0.7 mM in the fed and 5.8 +/- 1.0 mM in fasting state) compared with that of non-transgenic littermates (4.7 +/- 0.3 mM in the fed and 4.2 +/- 0.5 mM in fasting state). In the fed state, the rate of whole body glucose disposal was 70% higher in transgenic mice in the basal state, 81 and 54% higher during submaximal and maximal insulin stimulation. In the fasting state, insulin-stimulated whole body glucose disposal was also higher in the transgenic mice. Hepatic glucose production after an overnight fast was 24.8 +/- 0.7 mg/kg per min in transgenic mice, and 25.4 +/- 2.7 mg/kg per min in nontransgenic mice. Our data demonstrate that overexpression of Glut4 protein in muscle increases basal as well as insulin-stimulated whole body glucose disposal. These results suggest that skeletal muscle glucose transport is rate-limiting for whole body glucose disposal and that the Glut4 protein is a potential target for pharmacological or genetic manipulation for treatment of patients with non-insulin-dependent diabetes mellitus.     

Skeletal muscle and whole body protein turnover in cardiac cachexia: influence of branched-chain amino acid administration

Muscle protein wasting commonly accompanies severe heart failure. The mechanism of this so-called cardiac cachexia has been investigated in eight patients with an average body weight decrement of 19%, whose results have been compared with those from 11 healthy control subjects. Exchanges of tyrosine and 3-methylhistidine across leg tissue were used as specific indicators of net protein balance and myofibrillar protein breakdown, respectively. Whole body protein turnover was measured using a stable isotope labelling technique with L-[1-13C]leucine as tracer. In patients with cardiac cachexia there were greater values, relative to those values in normal control subjects, of leg efflux of tyrosine (-8.1 +/- 0.6 nmol 100 ml leg tissue-1 min-1 vs. -4.2 +/- 0.3 nmol 100 ml-1 min-1 (P less than 0.01) and of 3-methylhistidine (-0.8 +/- 0.1 nmol 100 ml leg tissue-1 min-1 vs. -0.1 +/- 0.02 nmol 100 ml-1 min-1 (P less than 0.005), mean +/- SEM). The results suggest that in patients with cardiac cachexia the state of net negative protein balance across leg tissue is associated with an increased rate of myofibrillar protein breakdown. In cardiac cachexia, neither efflux of tyrosine (-8.4 +/- 0.7 nmol 100 ml leg tissue-1 min-1) nor of 3-methylhistidine (-1.0 +/- 0.2 nmol 100 ml leg tissue-1 min-1) were significantly altered by branched-chain amino acid (BCAA) infusion to plasma concentrations of 1300 +/- 14 mumol ml-1, i.e., four times normal plasma values (282 +/- 11 mumol ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of whole-body protein turnover in insulin-dependent (type 1) diabetic patients during insulin withdrawal and infusion: comparison of [13C]leucine and [2H5]phenylalanine methodologies

1. The aims of this study were twofold: (i) to investigate the ability of a recently described [2H5]phenylalanine method for quantifying whole-body protein turnover during acute physiological perturbation; (ii) to determine specifically whether the previously observed increase in protein synthesis on insulin withdrawal in insulin-dependent (type 1) diabetic patients seen when employing the [13C]leucine technique could be corroborated by using [2H5]phenylalanine. 2. Whole-body protein turnover was measured by both the [2H5]phenylalanine and [13C]leucine primed continuous infusion methods applied simultaneously to six type I post-absorptive diabetic patients during insulin withdrawal and infusion. 3. Values were determined by the [13C]leucine method by measuring either [13C]leucine (primary pool) or alpha-[13C] ketoisocaproic acid (reciprocal pool) enrichment in plasma. 4. Values of whole-body protein breakdown during insulin withdrawal derived from the [2H5]phenylalanine and primary and reciprocal pool [13C]leucine models respectively were 3.54 +/- 0.43, 3.85 +/- 0.41 and 4.62 +/- 0.44 g day-1 kg-1 (means +/- SD). Insulin infusion resulted in a significant reduction (P less than 0.02) to 3.07 +/- 0.34, 3.05 +/- 0.26 and 3.82 +/- 0.4 g day-1 kg-1, respectively. Synthesis values fell significantly but by a smaller amount than breakdown, resulting in increased (P less than 0.05) net protein deposition, regardless of the model used. 5. These data demonstrate that the [2H5]phenylalanine and [13C]leucine methods generate similar results both in absolute and relative terms in response to short-term insulin infusion. 6. The confirmation of increased whole-body protein synthesis during insulin withdrawal by two independent methods supports the validity of this observation.     

肌营养不良蛋白表达在萎缩性肌病鉴别诊断中的意义

目的探讨肌营养不良蛋白(Dystrophin蛋白)在萎缩性肌病中的表达及其临床意义。方法对均表现为双下肢近端肌肉萎缩的43例肌营养不良患者、3例其他神经肌肉疾病患者(包括1例脂质沉积性肌病、2例运动神经元病)及5例正常对照者的骨骼肌标本进行Dystrophin蛋白免疫组化染色。结果 Duchenne型肌营养不良(DMD)患者肌细胞膜上无显色,Becker型肌营养不良(BMD)患者全部为弱阳性,BMD/LGMD(肢带型肌营养不良)患者中6例肌细胞膜上显色浅淡、不连续或呈斑片状,其余15例患者肌细胞膜上染色正常;2例运动神经元病患者中1例肌细胞膜显色浅淡、呈斑片状,另1例染色正常。脂质沉积性肌病患者和正常对照肌细胞膜上染色均正常。结论对于存在双下肢近端肌肉萎缩的临床表现相似的肌病患者,Dystrophin免疫组化染色可以将其大致区分,对早期预测肢体功能影响程度及正确地进行遗传咨询具有重要意义。     

Effect of alpha-human atrial natriuretic peptide on proteinuria in patients with primary glomerular diseases

1. The effects of synthetic alpha-human atrial natriuretic peptide (alpha-hANP) on urinary protein excretion were examined in nine healthy subjects and 20 patients with primary glomerular diseases who had proteinuria of 1.0 g or more per day. Synthetic alpha-hANP was intravenously infused into supine subjects at a rate of 8.3 pmol min-1 kg-1 for 40 min. 2. Before alpha-hANP infusion, the plasma concentration of immunoreactive alpha-hANP was significantly higher in the patients with glomerulonephritis than in the normal subjects (44.3 +/- 8.7 vs 19.4 +/- 3.0 pmol/l, mean +/- SEM, P less than 0.01) and it showed a positive correlation with mean arterial pressure (rs = 0.84, P less than 0.001) and a negative correlation with creatinine clearance (rs = -0.50, P less than 0.01). 3. During infusion of alpha-hANP, although the urinary excretion of protein did not change significantly in the normal subjects, it increased from 0.6 +/- 0.2 to 3.0 +/- 0.8 mg min-1 m-2 (P less than 0.001) in the patients with glomerulonephritis. The urinary protein/creatinine ratio did not change significantly in the former (from 0.18 +/- 0.05 to 0.22 +/- 0.06; NS), whereas it rose from 3.25 +/- 0.94 to 7.62 +/- 1.31 (P less than 0.001) in the latter. 4. The urinary excretions of albumin and of alpha 1-, alpha 2-, beta- and gamma-globulins, which were electrophoretically analysed, all increased in eight nephrotic patients during or immediately after infusion of alpha-hANP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased turnover of muscle contractile proteins in Duchenne muscular dystrophy as assessed by 3-methylhistidine and creatinine excretion.

1. Myofibrillar protein degradation has been measured in patients with Duchenne muscular dystrophy, normal boys, adult males and Duchenne carriers by the rate of 3-methylhistidine excretion after transfer of subjects to a meat-free diet. 2. Although absolute rates of protein breakdown are lower in Duchenne patients, expression of the data to allow for differences in muscle mass gives fractional degradation rates 2--3 times higher than in age-matched controls. 3. Fractional rates of muscle protein synthesis are increased in the Duchenne patients to almost the same extent as protein breakdown. 4. Rates of muscle protein breakdown in obligate and presumed carriers of the Duchenne gene are not different from controls.