Biomedical subjects

T E Graham

Publications and source records attributed to T E Graham.

At least 73 records · Page 4Linked to original sources

PubMed1992

Elevated muscle glycogen and anaerobic energy production during exhaustive exercise in man.

1. The effect of elevated muscle glycogen on anaerobic energy production, and glycogenolytic and glycolytic rates was examined in man by using the one-legged knee extension model, which enables evaluation of metabolism in a well-defined muscle group. 2. Six subjects performed very intense exercise to exhaustion (EX1) with one leg with normal glycogen (control) and one with a very high concentration (HG). With each leg, the exhaustive exercise was repeated after 1 h of recovery (EX2). Prior to and immediately after each exercise bout, a muscle biopsy was taken from m. vastus lateralis of the active leg for determination of glycogen, lactate, creatine phosphate (CP) and nucleotide concentrations. Measurements of leg blood flow and femoral arterial-venous differences for oxygen content, lactate, glucose, free fatty acids and potassium were performed before and regularly during the exhaustive exercises. 3. Muscle glycogen concentration prior to EX1 was 87.0 and 176.8 mmol (kg wet wt)-1 for the control and HG leg, respectively, and the decreases during exercise were 26.3 (control) and 25.6 (HG) mmol (kg wet wt)-1. The net glycogen utilization rate was not related to pre-exercise muscle glycogen concentration. Muscle lactate concentration at the end of EX1 was 18.8 (control) and 16.1 (HG) mmol (kg wet wt)-1, and the net lactate production (including lactate release) was 26.5 (control) and 23.6 (HG) mmol (kg wet wt)-1. Rate of lactate production was unrelated to initial muscle glycogen level. Time to exhaustion for EX1 was the same for the control leg (2.82 min) and HG leg (2.92 min). 4. Muscle glycogen concentration before EX2 was 14 mmol (kg wet wt)-1 lower than prior to EX1. During EX2 the muscle glycogen decline of 19.6 mmol (kg wet wt)-1 for the control leg was less than for the HG leg (26.2 mmol (kg wet wt)-1). The muscle lactate concentrations at the end of EX2 were about 7-8 mmol (kg wet wt)-1 lower compared to EX1, and the net lactate production was reduced by 40%. The exercise time during EX2 was 0.35 min shorter for the control leg, while no difference was observed for the HG leg. 5. Total reduction in ATP and CP was similar during the four exercise bouts, while a higher accumulation of inosine monophosphate (IMP) occurred during EX2 for the control leg (0.72 mmol (kg wet wt)-1) compared to the HG leg (0.20 mmol (kg wet wt)-1).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1992

Cardiovascular and norepinephrine responses of men and women to two cold pressor tests.

Two types of cold pressor tests were used to study gender differences in cardiovascular and plasma catecholamine responses. Ten male and ten female, young, healthy Caucasian subjects participated. The tests consisted of (1) 5 degrees C air blown at 3.5-4 m/s onto part of the face for 4 min and (2) the open right hand immersed to the wrist in water at 5 degrees C for 4 min. Heart rate, blood pressure (BP), and venous plasma norepinephrine were collected before, during, and 5 min after the 4 min of cold exposures. Test order was decided by a Latin square design, and the subjects rested in a quiet room for 30 min between the two tests. All parameters demonstrated significant (p less than 0.01) increases from rest during the cold tests. Gender differences were significant (p less than 0.01) in diastolic and systolic BP in each test with the males having a greater response, but gender differences were not found in heart rate or norepinephrine concentration. The study demonstrated that gender differences exist in the blood pressure responses to local cold, but that the mechanisms involved do not include a parallel difference in heart rate or venous plasma norepinephrine concentration.

Adult↗

PubMed1992

Ammonia and amino acid metabolism in human skeletal muscle during exercise.

This review focuses on the ammonia and amino acid metabolic responses of active human skeletal muscle, with a particular emphasis on steady-state exercise. Ammonia production in skeletal muscle involves the purine nucleotide cycle and the amino acids glutamate, glutamine, and alanine and probably also includes the branched chain amino acids as well as aspartate. Ammonia production is greatest during prolonged, steady state exercise that requires 60-80% VO2max and is associated with glutamine and alanine metabolism. Under these circumstances it is unresolved whether the purine nucleotide cycle (AMP deamination) is active; if so, it must be cycling with no IMP accumulation. It is proposed that under these circumstances the ammonia is produced from slow twitch fibers by the deamination of the branched chain amino acids. The ammonia response can be suppressed by increasing the carbohydrate availability and this may be mediated by altering the availability of the branched chain amino acids. The fate of the ammonia released into the circulation is unresolved, but there is indirect evidence that a considerable portion may be excreted by the lung in expired air.

Alanine↗

PubMed1992

Plasma amino acid and ammonia responses to altered dietary intakes prior to prolonged exercise in humans.

This study examined the effects of altered dietary intakes on amino acid and ammonia (NH3) responses prior to and during prolonged exercise in humans. Six male recreational cyclists rode to exhaustion at 75% of VO2max following 3 days on a low carbohydrate (LC), mixed (M), or high carbohydrate (HC) diet in a latin square design. There were differences (p less than 0.05) in exercise times among all treatments (58.8 +/- 3.7, 112.1 +/- 7.3, and 152.9 +/- 10.3 min for the LC, M, and HC treatments, respectively). The rate of increase in plasma NH3 during exercise was greater (p less than 0.05) during the LC trial. The LC trial was also characterized by higher (p less than 0.05) resting plasma concentrations of branched chain amino acids (BCAA) and a greater decrease in these amino acids during exercise (p less than 0.05), as compared with the other two treatments. Both plasma BCAA and NH3 were susceptible to dietary manipulations. These findings suggest that limited carbohydrate availability in association with increased BCAA availability results in enhanced BCAA metabolism during exercise. This is reflected in a greater rate of increase in plasma NH3 and is consistent with the hypothesis that a significant fraction of the NH3 released during a prolonged, submaximal exercise bout is from amino acid catabolism.

Adult↗

PubMed1992

Caffeine ingestion and muscle metabolism during prolonged exercise in humans.

We examined the effects of a high-caffeine dose on endurance performance and muscle acetyl group metabolism during prolonged exercise. Eight subjects cycled to exhaustion at approximately 80% maximal oxygen uptake (VO2max) 1 h after ingestion of 9 mg/kg body wt dextrose (Pl) or caffeine (Caf). In the Pl trial, muscle biopsies were taken at rest (1 h postingestion) and at 15 min and exhaustion during exercise. The Caf trial followed the same protocol 1 wk later, with an additional biopsy at the time corresponding to Pl exhaustion. The subjects cycled significantly longer during the Caf trial (96.2 +/- 8.8 min) than in the Pl trial (75.8 +/- 4.8 min). Net glycogenolysis during the initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 +/- 1.5 vs. 10.6 +/- 1.3 mmol.kg dry muscle-1.min-1; P less than 0.05). Muscle citrate concentration was increased at rest with Caf (0.59 +/- 0.07 vs. 0.37 +/- 0.05 mmol/kg dry muscle; P less than 0.05) but increased to similar values in both trials during cycling. Caf elevated the acetyl-CoA/CoA-SH ratio at rest (0.316 +/- 0.046 vs. 0.201 +/- 0.023; P less than 0.05) but had no effect on the increases in muscle acetyl-CoA and acetylcarnitine during exercise. The results indicate that Caf before exercise decreased muscle glycogenolysis by approximately 55% over the first 15 min of exercise at approximately 80% VO2max. This "spared glycogen" was available late in exercise and coincided with a prolonged time to exhaustion. Increased utilization of intramuscular triacylglycerol and/or extramuscular free fatty acids after caffeine ingestion may inhibit carbohydrate use at rest and early during exercise via elevations in muscle citrate and the acetyl-CoA/CoA-SH ratio. Muscle acetyl-CoA and acetylcarnitine were maintained above resting contents even at exhaustion when muscle glycogen was depleted.

Acetyl Coenzyme A↗

PubMed1991

Substrates for muscle glycogen synthesis in recovery from intense exercise in man.

1. Intramuscular glyconeogenesis from lactate after intense exercise was examined by using the one-legged knee extension model which enables evaluation of metabolism in a well-defined muscle group. 2. In seven subjects measurements of leg blood flow and arterial-venous differences of various substrates were performed in individuals after intense, exhaustive knee extensor exercise lasting 3.0 min. Muscle glycogen and lactate concentrations were determined in the quadriceps muscle immediately after exercise and three times during 1 h of recovery. 3. Muscle glycogen increased from 93.7 +/- 6.7 (+/- S.E.M.) to 108.8 +/- 8.1 mmol (kg wet wt)-1 during the recovery period. Muscle lactate was 27.1 +/- 2.1 mmol (kg wet wt)-1 at the end of exercise and decreased to 14.5 +/- 2.1, 6.7 +/- 1.1, and 3.0 +/- 0.5 mmol (kg wet wt)-1 after 3, 10 and 60 min of recovery, respectively. 4. More than two-thirds of the lactate that accumulated in the muscle during the intense exercise was released into the blood. It was estimated that between 13 and 27% of the lactate could have been converted to glycogen. This corresponded to a glycogen resynthesis rate from lactate of 0.17-0.34 and 0.002 mmol glucosyl units min-1 (kg wet wt)-1 for the first 10 and last 50 min of recovery, respectively. 5. The O2 debt of the leg was 1.5 l of which the resynthesis of ATP, creatine phosphate (CP) and glycogen and reloading of haemoglobin (Hb) and myoglobin (Mb) only could account for one-third. It is proposed that the elevated oxygen uptake during recovery is linked to the metabolic use of intramuscular triacylglycerol.

Adult↗

PubMed1991

Influence of fatty acids on ammonia and amino acid flux from active human muscle.

This study examined the dynamics of ammonia and amino acid exchange of human muscle during prolonged steady-state one-legged exercise at 80% of knee extensor maximal work capacity. Subjects (n = 10) performed leg extensor exercise for 1 h (control series), rested for 40 min while an infusion of Intralipid and heparin was begun, and then exercised the contralateral leg with the identical protocol [free fatty acid (FFA) series]. In the control series, ammonia efflux rose progressively, and 4.4 +/- 0.6 mmol were released in 1 h compared with 2.4 +/- 0.5 mmol (P less than 0.05) in the FFA series. The exercise was associated with large effluxes of total amino acids from the active muscle over the hour (12.8 +/- 4.3 and 10.3 +/- 3.3 mmol for control and FFA, respectively). Glutamine and alanine accounted for 47 and 64% of the efflux for the control and FFA series, respectively, while comparable values for essential amino acids were 24 and 20%. The latter implies that a net muscle protein catabolism was occurring during the exercise. The FFA treatment was associated not only with a reduced muscle ammonia release but also with a decreased (P less than 0.05) arterial concentration of nine amino acids (alanine, methionine, lysine, hydroxyproline, serine, glycine, proline, asparagine, and ornithine). Interpretation is limited due to the treatment order effect, but these data are compatible with the hypothesis that plasma clearance was affected by FFA.

Adult↗

PubMed1991

Substrate and hormonal responses to exercise in women using oral contraceptives.

Hormone and substrate responses to mild and heavy treadmill exercise were compared in women who used oral contraceptives (OC group; n = 7) and in normally menstruating women (control group; n = 8). Venous blood samples were obtained before exercise (-5 min), during exercise (15, 30, 45, and 60 min), and 30 min after exercise. All samples were analyzed for glucose, lactate, free fatty acids (FFA), glycerol, follicle-stimulating hormone (FSH), luteinizing hormone (LH), human growth hormone (hGH), cortisol, insulin, estradiol (E2), and progesterone (P). Substrate patterns during exercise were not altered by the phase of the menstrual cycle or OC usage. However, in the OC group the FFA concentrations were consistently higher during mild exercise and the glucose concentrations were lower at rest and during exercise than in the control group (P less than 0.05). No differences in lactate or glycerol responses were observed between the groups (P greater than 0.05). The responses of insulin and hGH to exercise were not related to the OC use per se but rather to the steroid status, either endogenous or exogenous. Specifically, during the steroid phases (OC use phase and luteal phase) 1) insulin concentrations were not quite as markedly reduced (i.e., 12% higher when luteal phase and OC usage phase data were combined; P less than 0.05), and 2) hGH concentrations at rest and during light exercise were higher in the OC group during the OC use phase (P less than 0.05). LH patterns were not affected by exercise (P greater than 0.05), but a slight decrease was found in FSH (P less than 0.05). Increments in P and E2 were observed in the control group in both the follicular and luteal phase (P less than 0.05), but much greater increments in P occurred in the luteal phase than in the follicular phase (P less than 0.05). In contrast to the control group, no increments in P, E2, or cortisol occurred in the OC users during exercise (P greater than 0.05). Therefore the new observations in this study are that 1) insulin and growth hormone respond in a complex manner during exercise with either the phase of the menstrual cycle or the phases of OC use and disuse and 2) the steroid concentrations (P, E2, cortisol) are increased in the controls but not in the OC users during exercise. The latter point suggests that normal steroid increments are due to an increased rate of secretion rather than a decrease in the hepatic clearance of these steroids.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1991

Influence of cold, exercise, and caffeine on catecholamines and metabolism in men.

Recently we found that caffeine ingestion did not enhance either thermal or fat metabolic responses to resting in cold air, despite an increase in plasma epinephrine and free fatty acids. Theophylline, another methylxanthine, has been shown to be effective during exercise but not at rest during cold stress. Therefore we hypothesized that caffeine ingestion before exercise in cold air would have a thermal-metabolic impact by increasing fat metabolism and increasing oxygen consumption. Young adult men (n = 6) who did not normally have caffeine in their diet performed four double-blind trials. Thirty minutes after ingesting placebo (dextrose, 5 mg/kg) or caffeine (5 mg/kg) they either exercised (60 W) or rested for 2 h in 5 degrees C air. Cold increased (P less than 0.05) plasma norepinephrine while both caffeine and exercise increased (P less than 0.05) epinephrine. Serum free fatty acids and glycerol were increased, but there were no differences between rest and exercise or placebo and caffeine. Caffeine had no influence on either respiratory exchange ratio or oxygen consumption either at rest or during exercise. The exercise trials did not significantly warm the body, and they resulted in higher plasma norepinephrine concentrations and lower mean skin temperatures for the first 30 min. The data suggest that skin temperature stimulates plasma norepinephrine while caffeine has little effect. In contrast, caffeine and exercise stimulate plasma epinephrine while cold has minimal effect. Within the limits of this study caffeine gave no thermal or metabolic advantage during a cold stress.

Adult↗

PubMed1991

Plasma and muscle amino acid and ammonia responses during prolonged exercise in humans.

Plasma and muscle amino acid (AA) and ammonia (NH3) responses were measured during prolonged submaximal exercise in humans. Increased NH3 production during submaximal exercise has been attributed to the activity of the purine nucleotide cycle, without consideration of any possible contribution from AA. Six men cycled at 75% of maximal O2 uptake until exhaustion on two occasions after 2.5 days of ingestion of a high-carbohydrate or mixed diet. Plasma samples (antecubital vein) and muscle biopsies (vastus lateralis) were obtained at rest and during exercise and analyzed for plasma and muscle NH3 and AA as well as muscle metabolites. There were no significant diet effects in these parameters, so the majority of results focus on the effects of exercise. Plasma and muscle NH3 increased significantly from the onset and continued to increase throughout exercise. The total and total essential [AA] of muscle were significantly increased at exhaustion, whereas both the plasma and muscle branched-chain AA contents were unchanged. This suggests that protein catabolism was occurring during exercise and the branched-chain AA were used for energy and NH3 production.

Adult↗

PubMed1991

Performance and metabolic responses to a high caffeine dose during prolonged exercise.

The present study examined whether a high caffeine dose improved running and cycling performance and altered substrate metabolism in well-trained runners. Seven trained competitive runners [maximal O2 uptake (VO2max) 72.6 +/- 1.5 ml.kg-1.min-1] completed four randomized and double-blind exercise trials at approximately 85% VO2max; two trials running to exhaustion and two trials cycling to exhaustion. Subjects ingested either placebo (PL, 9 mg/kg dextrose) or caffeine (CAF, 9 mg/kg) 1 h before exercise. Endurance times were increased (P less than 0.05) after CAF ingestion during running (PL 49.2 +/- 7.2 min, CAF 71.0 +/- 11.0 min) and cycling (PL 39.2 +/- 6.5 min, CAF 59.3 +/- 9.9 min). Plasma epinephrine concentration [EPI] was increased (P less than 0.05) with CAF before running (0.22 +/- 0.02 vs. 0.44 +/- 0.08 nM) and cycling (0.31 +/- 0.06 vs. 0.45 +/- 0.06 nM). CAF ingestion also increased [EPI] (P less than 0.05) during exercise; PL and CAF values at 15 min were 1.23 +/- 0.13 and 2.51 +/- 0.33 nM for running and 1.24 +/- 0.24 and 2.53 +/- 0.32 nM for cycling. Similar results were obtained at exhaustion. Plasma norepinephrine was unaffected by CAF at rest and during exercise. CAF ingestion also had no effect on respiratory exchange ratio or plasma free fatty acid data at rest or during exercise. Plasma glycerol was elevated (P less than 0.05) by CAF before exercise and at 15 min and exhaustion during running but only at exhaustion during cycling. Urinary [CAF] increased to 8.7 +/- 1.2 and 10.0 +/- 0.8 micrograms/ml after the running and cycling trials.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Prostate adenocarcinoma metastatic to the lung.

Metastatic adenocarcinoma of the prostate must be considered in the differential diagnosis of any pulmonary nodule in an elderly man. Pulmonary metastasis is not uncommon, although chest films show evidence of disease in only about 5% of cases. Computed tomography may be beneficial as a cost-effective tool in staging adenocarcinoma of the prostate and in aiding in biopsy of the lesion. Fine-needle aspiration cytology of pulmonary nodules and immunoperoxidase staining techniques provide a specific diagnostic means of differentiating metastatic adenocarcinoma of the prostate from primary lung carcinoma and aid in proper staging and treatment. The authors presented the case of an 83-year-old man with prostate adenocarcinoma metastatic to the lung. Diagnosis was based on a chest film and lung biopsy findings. The patient was treated with bilateral orchiectomy.

Adenocarcinoma↗

PubMed1990

Renal masses in adults. Differentiating benign from neoplastic causes.

Diagnostic evaluation of renal masses in adults has been a perplexing problem. With the advent of new imaging methods over the past 15 to 20 years, the best approach has varied from institution to institution, depending on the equipment available and the preference of the physician. A diagnostic algorithm is presented here to guide the physician in determining the order in which certain techniques should be considered, thus avoiding unnecessary tests and cutting healthcare costs. In general, benign masses, malignant masses, and pseudoneoplasms have characteristic features that distinguish them from each other if the physician knows how to use the various imaging techniques and interpret results.

Adult↗

PubMed1990

Anaerobic energy production and O2 deficit-debt relationship during exhaustive exercise in humans.

1. Eight subjects performed one-legged, dynamic, knee-extensor exercise, first at 10 W followed by 10 min rest, then at an intense, exhaustive exercise load (65 W) lasting 3.2 min. After 60 min recovery, exercise was performed for 8-10 min each at 20, 30, 40 and 50 W. Measurements of pulmonary oxygen uptake, heart rate, blood pressure, leg blood flow, and femoral arterial-venous differences of oxygen content and lactate were performed as well as determination of ATP, creatine phosphate (CP) inosine monophosphate (IMP) and lactate concentrations on biopsy material from the quadriceps muscle before and immediately after the intense exercise, and at 3, 10 and 60 min into recovery. 2. Individual linear relations (r = 0.95-1.00) between the power outputs for submaximal exercise and oxygen uptakes (leg and pulmonary) were used to estimate the energy demand during intense exercise. Pulmonary and leg oxygen deficits determined as the difference between energy demand and oxygen uptake were 0.46 and 0.48 l (kg active muscle)-1, respectively. Limb and pulmonary oxygen debts (oxygen uptake during 60 min of recovery - pre-exercise oxygen uptake) were 0.55 and 1.65 l (kg active muscle)-1, respectively. 3. During the intense exercise, muscle [ATP] decreased by 30% and [CP] by 60% from resting concentrations of 6.2 and 22.4 mmol (kg wet wt)-1, respectively, and [IMP] increased to 1.1 mmol (kg wet wt)-1. Muscle [lactate] increased from 2 to 28.1 mmol (kg wet wt)-1, and the concomitant net lactate release was 14.8 mmol (kg wet wt)-1 or about 1/3 of the total net lactate production. During recovery 70% of the accumulated lactate was released to the blood, and the nucleotides and CP returned to about 40 and 85% of pre-exercise values at 3 and 10 min of recovery, respectively. 4. Total reduction in ATP and CP (and elevation of IMP) during the intense exercise amounted to 16.4 mmol ATP (kg wet wt)-1, which together with the lactate production accounted for 83.1 mmol ATP (kg wet wt)-1. In addition 6-8 mmol ATP (kg wet wt)-1 are made available related to accumulation of glycolytic intermediates including pyruvate (and alanine). Estimated leg oxygen deficit corresponded to an ATP production of 94.7 mmol ATP kg-1; this value included 3.1 mmol kg-1 related to unloading of HbO2 and MbO2.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1990

Effect of acidosis on skeletal muscle metabolism with and without propranolol.

Does the stimulatory effect of circulating catecholamines counteract the inhibitory effect of acidosis on skeletal muscle metabolism? To investigate this possibility, we studied gastrocnemii in dogs breathing either air (n = 10) or 4% carbon dioxide in air (n = 10) at rest and during contractions. In five dogs from each group, we infused propranolol into the arterial supply of the right and left muscles for 40 min. After 30 min of infusion, the left muscle was stimulated at 3 Hz for 10 min. During the 10th min of contractions, we removed and froze both muscles in liquid nitrogen. Oxygen uptake and blood flow to the left muscle prior to or during stimulation was not affected by acidosis either with or without propranolol. Glycogen concentration in resting muscle was unaffected by acidosis with or without propranolol. There was an acidosis related decrease of approximately 50% in the glycolytic intermediates (glucose 6-phosphate, fructose 1,6-diphosphate, alpha-glycerol phosphate, and dihydroxyacetone phosphate) in unstimulated muscles without beta-blockade. At rest, acidosis decreased muscle lactate by 50% with and 64% without propranolol, but lactate release was decreased only with acidosis without propranolol (1.4-0.1 mumols/kg.s). Acidosis without propranolol had no effect on the changes in glycogen concentration or the change in the concentration of glycolytic intermediates resulting from contractions. In beta-blocked muscle, the difference between stimulated and unstimulated concentrations of glycogen and glycolytic intermediates including lactate was 20-50% smaller with acidosis. Thus, with beta-blockade, the acidotic effects at rest disappeared and an inhibition of the metabolic adjustment to contractions appeared, indicating that circulating catecholamines do modify some metabolic effects of acidosis.

Acidosis↗

PubMed1990

Ammonia metabolism during intense dynamic exercise and recovery in humans.

This study examined the dynamics for ammonia (NH3) metabolism in human skeletal muscle during and after intense one-legged exercise. Subjects (n = 8) performed dynamic leg extensor exercise to exhaustion (3.2 min). Muscle NH3 release increased rapidly to a maximum of 314 +/- 42 mumol/min and declined immediately on cessation of exercise. Recovery was complete in approximately 20 min. Arterial [NH3] increased less rapidly and reached its maximum 2-3 min into recovery. These data demonstrate that NH3 clearance is more sensitive to the cessation of exercise than is NH3 release from skeletal muscle. Muscle [NH3] increased three to fourfold during exercise and represented 74 +/- 8% of the total net NH3 formation. Thus the change in muscle [NH3] alone underestimates the NH3 production. There was no evidence that the muscle-to-venous blood NH3 ratio shifts in accordance with the H+ data. Thus other factors must contribute to the NH3 release from active muscle. The total net NH3 formed corresponded with the intramuscular inosine 5'-monophosphate accumulation, suggesting that the NH3 was derived from AMP deamination. Changes in the known modulators of AMP deaminase (ATP, ADP, H+) were moderate, so the mechanisms initiating the deamination remain obscure.

Adenine Nucleotides↗

PubMed1990

Glycogen content has no effect on skeletal muscle glycogenolysis during short-term tetanic stimulation.

The effect of skeletal muscle glycogen content on in situ glycogenolysis during short-term tetanic electrical stimulation was examined. Rats were randomly assigned to one of three conditions: normal (N, stimulated only), supercompensated (S, stimulated 21 h after a 3-h swim), and fasted (F, stimulated after a 20-h fast). Before stimulation, glycogen contents in the white (WG) and red gastrocnemius (RG) and soleus (SOL) muscles were increased by 13-25% in S and decreased by 15-27% in F compared with N. Hindlimb blood flow was occluded 60 s before stimulation to produce a predominantly anaerobic environment. Muscles were stimulated with trains of supramaximal impulses (100 ms at 80 Hz) at a rate of 1 Hz for 60 s. Muscle glycogenolysis was measured from the decrease in glycogen content and estimated from the accumulation of glycolytic intermediates in the closed system. The resting glycogen content had no effect on measured or estimated glycogenolysis in all muscles studied. Average glycogenolysis in the WG, RG, and SOL muscles was 98.4 +/- 4.3, 60.9 +/- 4.0, and 11.2 +/- 3.6 mumol glucosyl U/g dry muscle, respectively. Hindlimb tension production was similar across conditions. The results suggest that in vivo glycogen phosphorylase activity in skeletal muscle is not regulated by the content of its substrate glycogen (range 80-165 mumol/g) during short-term tetanic stimulation in an anaerobic environment.

Adenosine Triphosphate↗

PubMed1990

Influence of caffeine on metabolic responses of men at rest in 28 and 5 degrees C.

Cold stress and caffeine ingestion are each reported to increase plasma catecholamines, free fatty acid (FFA) concentrations, and energy metabolism. This study examined the possible interaction of these two metabolic challenges in four double-blind counterbalanced trials. Young adult men (n = 6) ingested caffeine (5 mg/kg) or placebo (dextrose, 5 mg/kg) and rested for 2 h in 28 or 5 degrees C air. Cold stress alone elevated (P less than 0.05) plasma norepinephrine, metabolism (O2 consumption, VO2), and respiratory exchange ratio (RER). Caffeine alone increased (P less than 0.05) plasma epinephrine and FFA but not RER. When the two challenges were combined (caffeine plus 5 degrees C for 2 h) norepinephrine and epinephrine were increased (P less than 0.05) as was FFA. However, VO2, RER, and skin and rectal temperatures were not different from the responses observed at 5 degrees C after placebo ingestion. The data suggest that caffeine selectively increases plasma epinephrine, whereas cold air increases norepinephrine. During the cold exposure, increasing epinephrine and FFA above normal levels did not appear to influence the metabolic or thermal responses to the cold stress. In fact the increase in RER suggested a greater carbohydrate oxidation.

Acclimatization↗