F. Pirnay

Quantitative Evaluation of the Oxidation of an Exogenous Glucose Load Using Naturally Labeled 13C-Glucose

Maize glucose was used as a natural tracer for studies of metabolism. It is richer in 13C than common vegetables and foods derived from these, and the C02 formed from it is consequently richer in 13C than the CO2 expired by man fed on a diet of common vegetables. The quantitative results, obtained by measurement of delta 13C of the expired CO2 and of VCO2 during the oxidation of an exogenous glucose load (about 100 g) in eight normal subjects over 7 hr, have shown a consumption of 28.64 +/- 1.44 g of glucose (mean +/- SEM), which represents about 30% of the load given. A comparison is made with the results obtained from other methods and the originality and usefulness of this new quantitative procedure is outlined.

Effect of glucose ingestion on energy substrate utilization during prolonged muscular exercise

SummaryThe distribution of substrates utilized during prolonged exercise was investigated in normal human volunteers with and without ingestion of 100 g exogenous glucose. The energy provided by protein oxidation was derived from urinary nitrogen excretion and the total energy provided by carbohydrates and lipids was calculated from respiratory quotient (RQ) determinations. The contribution of exogenous glucose to the energy supply was determined by an original procedure using “naturally labeled 13C-glucose” as metabolic tracer. Protein oxidation provided between 1 and 2% of the total energy requirement; this amount was not affected by glucose ingestion. In the absence of exogenous glucose ingestion, carbohydrate were progressively replaced by lipids as source of energy. Exogenous glucose contributed markedly to total carbohydrate oxidation and decreased the percentage of energy derived from lipids. In addition, ingestion of exogenous glucose resulted in a significant economy of endogenous carbohydrates and permitted to prolong the duration of exercise.

Anaerobic and aerobic power of top athletes

SummaryIn this study the alactic anaerobic and aerobic power of top level sprinters, long-distance runners, and untrained students were compared. Maximal oxygen uptake was measured during a progressive test on a treadmill. The anaerobic power was estimated according to a newly developed bicycle ergometer technique. As reported elsewhere, the maximal oxygen uptake is very high in twelfe long-distance runners (77.6±2.7 ml/kg·min−1) whereas the maximal oxygen uptake of six sprinters amounts to 60.1±5.9 ml/kg·min−1.The average alactic anaerobic power of a control group of 32 students was 710 W or 10.1±1.2 W/kg. Significantly lower results were obtained by long-distance runners (551 W or 8.93 W/kg) whereas significantly higher results were obtained by sprinters (1,021 W or 14.16 W/kg). In top level athletes, but not in the control group, a negative relationship was found between aerobic power and anaerobic power.

Glucose Utilization During Exercise in Normal and Diabetic Subjects: The Role of Insulin

Due to selective isotopic effects occurring during photosynthesis, certain natural sugars are enriched in 13C Using such “naturally labeled 13C-glucose,” we studied glucose oxidation during exercise in seven normal volunteers and in six insulin-dependent diabetics after an overnight fast. In the diabetics, blood glucose was monitored the night before the test and adjusted to about 100 mg/dl by intravenous insulin infusion. The insulin infusion was withheld 15 min before exercise in four diabetics and maintained at 0.9 U/h for 2 h; then it was maintained at 0.6 U/h for 2 h in five diabetics. Three patients underwent both tests. All subjects exercised on a treadmill for 4 h at about 45% of their max. After 15 min adaptation, all received 100 g 13C-labeled glucose orally. Total glucose oxidation was derived from non-protein RQ and exogenous glucose oxidation evaluated as previously described. The diabetics had no residual B-cell function as indicated by negligible plasma C-peptide values and a lack of Cpeptide response to the oral glucose challenge. Total glucose oxidation averaged 230 ± 14 g/4 h in the normal subjects. It was similar (238 ± 19 g/4 h) in the diabetics receiving an intravenous insulin infusion, but decreased to 176 ± 14 g/4 h when no insulin was infused. Exogenous glucose oxidation was 92 ± 3 g/4 h and 84 ± 8 g/4 h (not statistically different) in the controls and in the insulin-infused diabetics, respectively. It was 43 ± 11 g/4 h in the diabetics exercising without being infused with insulin. We conclude that (1) in well-insulinized diabetic patients, prolonged muscular exercise can be performed under metabolic conditions which are basically similar to those of normal subjects; (2) during prolonged exercise, well-insulinized diabetic patients are able to oxidize up to 85–90% of a 100-g exogenous glucose load given orally and oral glucose can thus be ingested during prolonged exercise in well-controlled juvenile insulintreated diabetics; (3) even in the absence of insulin administration during exercise, juvenile diabetics who start exercising when blood glucose is near normal are able to perform a 4-h exercise at 45–50% of their max. Under these conditions, however, they are unable to utilize more than 40–45% of a 100-g glucose load given orally. They rely more upon lipid stores than the normal subjects or the well-insulinized diabetics.

Effect of glucose on plasma glucagon and free fatty acids during prolonged exercise

SummaryThe effects of glucose ingestion on the changes in blood glucose, FFA, insulin and glucagon levels induced by a prolonged exercise at about 50% of maximal oxygen uptake were investigated. Healthy volunteers were submitted to the following procedures: 1. a control test at rest consisting of the ingestion of 100 g glucose, 2. an exercise test without, or 3. with ingestion of 100 g of glucose. Exercise without glucose induced a progressive decrease in blood glucose and plasma insulin; plasma glucagon rose significantly from the 60th min onward (+45 pg/ml), the maximal increase being recorded during the 4th h of exercise (+135 pg/ml); plasma FFA rose significantly from the 60th min onward and reached their maximal values during the 4th h of exercise (2177±144 ΜEq/l, m±SE). Exercise with glucose ingestion blunted almost completely the normal insulin response to glucose. Under these conditions, exercise did not increase plasma glucagon before the 210th min; similarly, the exercise-induced increase in plasma FFA was markedly delayed and reduced by about 60%. It is suggested that glucose availability reduces exercise-induced glucagon secretion and, possibly consequently, FFA mobilization.

Utilization of Oral Sucrose Load During Exercise in Humans: Effect of the α-Glucosidase Inhibitor Acarbose

We investigated the hormonal and metabolic response to a 100-g sucrose load given 15 min after adaptation to moderate-intensity (50% Vmaxo2) long-duration (4-h) exercise in healthy volunteers. The effect of a 100-mg dose of the α-glucosidase inhibitor Acarbose ingested with the sucrose load was also investigated. “Naturally labeled [13C] sucrose” was used to follow the conversion to expired-air CO2 of the sugar ingested by isotope-ratio mass spectrometry. Circulating hormone and metabolite data were obtained in nine subjects, and indirect calorimetry and stable isotope methodology were applied to six of them. Under placebo, 93 ± 4 g sucrose were entirely oxidized during the 4 h of exercise, total carbohydrate utilization was 235 ± 14 g, endogenous carbohydrate utilization was 142 ± 13 g, and total lipid oxidation was 121 ± 7 g. A single oral dose of 100 mg Acarbose ingested with the sucrose load did not significantly modify total carbohydrate (239 ± 2 g/4 h) or lipid (122 ± 6 g/4 h) oxidation. In contrast, sucrose oxidation was reduced to 53 ± 6 g/4 h and endogenous carbohydrate utilization increased to 186 ± 7 g/4 h. Reduction of the rises in blood glucose and fructose and of the increases in plasma insulin and C peptide under Acarbose confirmed these effects, whereas lower circulating levels of alanine suggested a higher rate of gluconeogenesis. These data show that a 100-g glucose load ingested soon after initiation of exercise is a perfect available metabolic substrate. Furthermore, the simultaneous ingestion of 100 mg Acarbose significantly reduces the availability of sucrose during exercise, a finding that has to be considered if this or other compounds with similar properties are envisaged for the treatment of diabetic patients.

Should we exclude elderly patients with chronic obstructive pulmonary disease from a long-time ambulatory pulmonary rehabilitation programme?

OBJECTIVE To assess the outcomes of a 6-month comprehensive multidisciplinary outpatient pulmonary rehabilitation programme in patients with chronic obstructive pulmonary disease according to age. DESIGN Prospective cohort study. PATIENTS A total of 140 patients with chronic obstructive pulmonary disease (Global Initiative for Chronic Obstructive Lung Disease (GOLD) 3-4) admitted to our centre for pulmonary rehabilitation. METHODS Patients were divided into 3 groups: group A (< 65 years), group B (65-74 years) and group C (≥ 75 years). All the patients received an education and individualized training programme. Pulmonary rehabilitation efficacy was evaluated at 6 months of treatment and 12 months post-treatment. RESULTS A total of 116 patients completed the pulmonary rehabilitation programme: 59 in group A (85.5%), 40 in group B (80%) and 17 in group C (80.9%). All the parameters studied (number of sessions, 6-min walking distance, isometric quadriceps strength, health-related quality of life, maximal load, peak oxygen uptake, maximal inspiratory and expiratory pressures) were significantly improved in each of the groups at 3 and 6 months compared with baseline. Moreover, percentage changes from baseline at 6 months for all of the parameters studied were not significantly different between age-groups. CONCLUSION Pulmonary rehabilitation is efficient in elderly patients with severe and very severe chronic obstructive pulmonary disease, and their compliance with pulmonary rehabilitation was similar to that seen in younger groups. Therefore, elderly patients with chronic obstructive pulmonary disease should not be denied pulmonary rehabilitation.

Influence of water temperature on thermal, circulatory and respiratory responses to muscular work

SummaryDifferent muscular exercises have been executed on a bicycle ergometer during immersion in water, the temperature of which varied between 20 and 40‡ C. During submaximal works, O2 consumption was not modified by the temperature of the water. On the other hand, body temperatures (rectal and muscular) are clearly influenced by environment. The temperature of the quadriceps varies from 37.7–38.5‡ C when the bath temperature rises from 20–40‡ C during the same work intensity corresponding to 1/3 of the individual maximal work capacity. The rectal temperature was always lower about 0.5‡ C. Ventilation and heart rate underwent modifications which were significantly accentuated in hot water.Maximal O2 consumption does not reach its highest level in cold water. The low muscular temperature observed in these conditions seems to limit the aerobic metabolism and the working of the muscles. Maximal O2 consumption then rises in parallel with the increase in bath temperature and in body temperatures. In very hot water however (40‡ C), when rectal temperature rises unduly, the circulatory demand linked to thermolysis becomes excessive, and maximal O2 consumption decreases.

Exercise during hyperoxia and hyperbaric oxygenation

Physiological reactions during exercise were tested under hyperoxic and hyperbaric conditions. In 6 subjects walking and running at increasing speeds on a treadmill, maximum performance showed little change when the respired air was enriched with O2. Maximum metabolism, measured by CO2 production, increased by 3.2%. During exercise on a bicycle ergometer, maximum O2 uptake increased by 3% in 5 subjects breathing pure O2 at 1 ATA. During hyperoxia the maximum O2 consumption measured at 2 and 3 ATA did not differ significantly from that measured at 1 ATA. Heart rate showed highly comparable maximum values under the various experimental conditions. During submaximal exercise, heart rate was consistently lower when the subjects breathed O2. The O2-linked difference became slighter with every increase in work load. Under hyperbaric and hyperoxic conditions, ventilation was invariably reduced during exercise.

Availability of glucose ingested during muscle exercise performed under acipimox-induced lipolysis blockade

This study investigated the percentage of carbohydrate utilization than can be accounted for by glucose ingested during exercise performed after the ingestion of the potent lipolysis inhibitor Acipimox. Six healthy male volunteers exercised for 3 h on a treadmill at about 45% of their maximal oxygen uptake, 75 min after having ingested 250 mg of Acipimox. After 15-min adaptation to exercise, they ingested either glucose dissolved in water, 50 g at time 0 min and 25 g at time 60 and 120 min (glucose, G) or sweetened water (control, C). Naturally labelled [13C]glucose was used to follow the conversion of the ingested glucose to expired-air CO2. Acipimox inhibited lipolysis in a similar manner in both experimental conditions. This was reflected by an almost complete suppression of the exercise-induced increase in plasma free fatty acid and glycerol and by an almost constant rate of lipid oxidation. Total carbohydrate oxidation evaluated by indirect calorimetry, was similar in both experimental conditions [C, 182, (SEM 21); G, 194 (SEM 16) g · 3 h−1], as was lipid oxidation [C, 57 (SEM 6); G, 61 (SEM 3) g · 3 h−1]. Exogenous glucose oxidation during exercise G, calculated by the changes in13C:12C ratio of expired air CO2, averaged 66 (SEM 5) g · 3 h−1 (19% of the total energy requirement). Consequently, endogenous carbohydrate utilization was significantly smaller after glucose than after placebo ingestion: 128 (SEM 18) versus 182 (SEM 21) g · 3 h−1, respectively (P < 0.05). Symptoms of intense fatigue and leg cramps observed with intake of sweet placebo were absent with glucose ingestion.In conclusion, we found glucose ingestion during 3-h exercise with lipolysis blockade could provide metabolic substrate permitting a significant sparing of endogenous carbohydrate and consequently an improvement in performance.