Fuel metabolism during exercise in normal and diabetic man

Nutrients utilization in obese individuals with and without hypertriglyceridemia

Background: Low fat utilization is linked to weight gain and to the presence of certain atherosclerosis markers. It is not clear whether the presence of hyperlipidemia can further affect nutrients utilization. The main objective of this study was to investigate the fasting fuel utilization of obese subjects suffering from hypertriglyceridemia, and to compare it with that of individuals that are solely obese. Method: We recruited 20 obese individuals with hypertriglyceridemia and 20 matched individuals not affected by hypertriglyceridemia. The fuel utilization (respiratory quotient) was measured by respiratory gas exchange, by Indirect Calorimetry. Results: There was a significant difference in fuel utilization and HDL-cholesterol between cases and controls (respiratory quotient 0.89 ± 0.07 vs. 0.84 ± 0.06; p = 0.020 respectively). The univariate and multivariate linear regression analysis confirmed that hypertrygliceridemia was positively correlated to the respiratory quotient (p = 0.035). Conclusion: obese subjects with hypertriglyceridemia had a higher respiratory quotient in comparison to unaffected subjects. This could suggest a limitation in the beta-oxidation mechanisms; this could actually imply that fatty acids may be redirected from oxidation to reesterification into triglycerides. The study could suggest the presence of different mechanisms unrelated to obesity and also a potential new therapeutic target for hypertriglyceridemia management.

Assessment of myocardial triglyceride oxidation with PET and 11C-palmitate

BACKGROUND

The goal of this study was to test whether myocardial triglyceride (TG) turnover including oxidation of TG-derived fatty acids (FA) could be assessed with PET and (11)C-palmitate.

METHODS AND RESULTS

A total of 26 dogs were studied fasted (FAST), during Intralipid infusion (IL), during a hyperinsulinemic-euglycemic clamp without (HIEG), or with Intralipid infusion (HIEG + IL). (11)C-palmitate was injected, and 45 minutes were allowed for labeling of myocardial TG pool. 3D PET data were then acquired for 60 minutes, with first 15 minutes at baseline followed by 45 minutes during cardiac work stimulated with constant infusion of either phenylephrine (FAST, n = 6; IL, n = 6; HIEG + IL, n = 6) or dobutamine (FAST, n = 4; HIEG, n = 4). Myocardial (11)C washout during adrenergic stimulation (AS) was fitted to a mono-exponential function (Km(PET)). To determine the source of this (11)C clearance, Km(PET) was compared to direct coronary sinus-arterial measurements of total (11)C activity, (11)C-palmitate, and (11)CO(2). Before AS, PET curves in all groups were flat indicating absence of net clearance of (11)C activity from heart. In both FAST groups, AS resulted in negligible net (11)C activity and (11)CO(2) production higher than net (11)C-palmitate uptake. AS with phenylephrine resulted in net myocardial uptake of total (11)C activity and (11)C-palmitate in IL and HIEG + IL, and (11)CO(2) production lower than (11)C-palmitate uptake. In contrast, AS with dobutamine in HIEG resulted in net clearance of all (11)C metabolites (total (11)C activity, (11)C-palmitate and (11)CO(2)) with (11)CO(2) contributing 66% to endogenous FA oxidation. The AS resulted in significant Km(PET) in all the groups, except HIEG + IL. However, positive correlation between Km(PET) and (11)CO(2) was observed only in HIEG (R (2) = 0.83, P = .09).

CONCLUSIONS

This is the first study to demonstrate that using PET and pre-labeling of intracardiac TG pool with (11)C-palmitate, noninvasive assessment of myocardial TG use is feasible under metabolic conditions that favor endogenous TG use such as increased metabolic demand (beta-adrenergic stimulation of cardiac work) with limited availability of exogenous substrate (HIEG).

Exercise capacity in subjects with type 1 diabetes mellitus in eu- and hyperglycaemia

BACKGROUND

Circumstantial evidence suggests that an increase in plasma glucose availability improves exercise capacity in subjects with type 1 diabetes mellitus. The aim of this study was to assess exercise capacity in eu- and hyperglycaemic conditions in subjects with type 1 diabetes.

METHODS

Eight moderately exercise-trained male subjects with type 1 diabetes on continuous subcutaneous insulin infusion were studied. Using identical insulin infusion rates, the patients were randomly allocated to perform two stepwise ergometer tests in eu- and hyperglycaemic clamp conditions. The primary endpoint was the peak power output; the secondary endpoints comprised the rate of perceived exertion, lactate levels, heart rate, and respiratory exchange ratio.

RESULTS

Eu- and hyperglycaemic clamp conditions were observed at a plasma glucose concentration of 5.3 +/- 0.6 mmol/L and 12.4 +/- 2.1 mmol/L, respectively (mean +/- SD), and remained stable throughout the physical exercise. Insulin levels were similar in both conditions. Hyperglycaemia did not result in a significant increase in the peak power output compared to euglycaemia (mean paired difference of 4.96 W, 95% CI - 11.3 to 21.2, p = 0.49). Hyperglycaemia did not have a significant impact on the secondary endpoints compared to euglycaemia. Sensitivity analyses confirmed these results.

CONCLUSIONS

In subjects with type 1 diabetes, exercise capacity is not influenced by hyperglycaemia. Comparable levels of lactate and similar respiratory exchange ratio suggest that an increase in extracellular glucose availability did not translate into increased intracellular glucose oxidation.

Benefícios da atividade física no perfil lipídico de pacientes com diabetes tipo 1

Avaliamos a resposta do perfil lipídico a uma intervenção não-farmacológica de curta duração, e investigamos se alterações nas lipoproteínas estavam presentes, antes da nefropatia diabética (ND) clínica, em 46 pacientes jovens com diabetes tipo 1 (DM1), com idade de 15,5±1,5 anos submetidos a um programa de 8 dias de dieta apropriada e exercícios, durante controle glicêmico estável (glicemia média 110,3±27,1mg/dl e HbA1c 6,9±1,3%). No início, 65% dos jovens apresentavam colesterol total > 160mg/dl (IC 95% 0,51-0,78), enquanto que ao final somente 38% (IC 95% 0,24-0,51) tinham tais níveis. A melhora no perfil lipídico foi ainda melhor para a fração LDL, considerando que inicialmente 67% mostravam valores acima de 100mg/dl (IC 95% 0,55-0,78) e 24% (IC 95% 0,12-0,36) ao final. Valores de HDL-colesterol subnormais (< 40mg/dl) ocorreram em 38% (95% IC 0,24-0,51) e 11% (IC 95% 0,02-0,20) deles, no início e final do período. A razão albumina/creatinina média foi 9,0±8,0mg/g de creatinina. Encontramos fracas correlações entre a razão albumina/creatinina e os níveis de colesterol total (r= 0,21), LDL (r= 0,24), VLDL (r= 0,30), HDL (r= -0,17) e de triglicérides (r= 0,31). Dentro da faixa de referência de albuminúria, não foi encontrada nenhuma associação entre a excreção urinária de albumina e os níveis de lípides nos pacientes com DM1 estável. Um programa de exercícios regulares é eficaz em otimizar o perfil lipídico nestes pacientes, independentemente do controle glicêmico. Nossos dados não apoiam a hipótese de que mudanças no metabolismo lipídico precederiam a microalbuminúria no curso da ND.

The effect of walking before and after breakfast on blood glucose levels in patients with type 1 diabetes treated with intensive insulin therapy

OBJECTIVE

We examined the effect of walking at different timing on carbohydrate metabolism in patients with type 1 diabetes.

SUBJECTS AND METHODS

Subjects included six non-obese patients treated with intensive insulin therapy. The blood glucose profile was determined with and without walking for 30 min before (ExBM) or after (ExAM) breakfast.

RESULTS

Mean blood glucose values at 07:00 h in the control, ExBM, and ExAM were 9.0, 8.0, 8.8 mM, respectively. Glucose levels gradually increased after meals up to 13.6, 15.0, and 15.3 mM, respectively, at 09:00 h (0.5 h after meals). At 09:30 h, glucose levels significantly fell to 11.0 mM during walking in the ExAM (P=0.039 vs 09:00 h values). The area under blood glucose response curve was significantly lower only in the ExAM when compared with that in the control (P=0.043) (11.8, 17.8. and 3.8 h mM in the control, ExBM and ExAM, respectively).

CONCLUSION

These results might suggest that walking after meals improves glycemic control in patients with type 1 diabetes being treated with intensive insulin therapy consisting of the basal-bolus (NPH-human regular) insulin regimen.

Determinants of haemostatic risk factors for coronary heart disease in obese children and adolescents

OBJECTIVE

To investigate the contribution of serum lipids, parameters of glucose metabolism, body composition and cardiovascular fitness to the variance of several haemostatic risk factors for coronary heart disease (CHD) in obese children and adolescents.

SUBJECTS AND MEASUREMENTS

Forty-two healthy, obese children and adolescents (20 male, 22 female, age 12.6 +/- 3.2y; body mass index (BMI), 30.4 +/- 5.3 kg/m2), were screened for haemostatic and metabolic risk factors for CHD. Thirty-five of the participants (18 male, age 13.5 +/- 2.9y; BMI, 29.9 +/-4.5kg/m2; 17 female, age 12.8+/-2.1 y, BMI, 31.1 +/- 5.3 kg/m2) were assessed for cardiovascular fitness by means of incremental cycle ergometer exercise.

RESULTS

After adjustment for age, fat mass correlated significantly with plasminogen activator inhibitor-1 antigen (PAI-1-Ag) in boys and girls and factor VIIc only in girls. Children with lower power output (< or = 2.77W/kg) showed significantly higher values for factor VIIc, fibrinogen and tissue-type plasminogen activator antigen (tPA-Ag). Neither body composition nor cardiovascular fitness contributed independently to the variance of the determined haemostatic risk factors, except PAI-1-Ag, which has been shown to be determined by fat mass. In multiple linear regression analysis, triglycerides and PAI-1-Ag explained significant independent proportions of the variance of tPA-Ag. Factor VIIc was explained by C-peptide, insulin and fibrinogen. Von Willebrand factor antigen (vWF-Ag) was significantly related to glucose and insulin.

CONCLUSION

The results suggest that in obese children and adolescents the haemostatic risk factors factor VIIc, vWF-Ag and tPA-Ag are mainly determinated by plasma insulin and triglyceride concentrations, but are primarily independent of body composition and cardiovascular fitness.

Alcohol and postexercise metabolic responses in type 2 diabetes

The objective was to investigate the impact of the combination of exercise and alcohol on the metabolic response in nonfasting and fasting type 2 diabetic subjects. In part 1, 12 untrained middle-aged type 2 diabetic subjects participated on 3 test days. On each day, they ingested a light meal (1,824 kJ) containing 48 energy percent (E%) carbohydrate, 38 E% fat, and 14 E% protein. The meal was followed by either (A) rest or (B) 30 minutes of exercise (40% of maximum O2 consumption [VO2max]) or (C) taken with alcohol (0.4 g/kg body weight) followed by 30 minutes of exercise (40% of VO2max). In part 2, 11 untrained middle-aged type 2 diabetic subjects participated on 4 test days without a meal. The subjects were either (A) resting, (B) drinking alcohol (0.4 g/kg body weight), (C) exercising 30 minutes (40% of VO2max), or (D) drinking alcohol (0.4 g/kg body weight) and exercising 30 minutes (40% of VO2max). On each test day, regular blood samples were drawn for 4 hours for analysis of glucose, insulin, lactate, triglycerides, nonesterified fatty acid (NEFA), and ethanol. Comparing exercise and rest following a light meal (part 1, no change (7%) occurred in the plasma glucose response area (642 +/- 119 v 724 +/- 109 mmol x L(-1) x 240 min, NS). However, it was significantly reduced (by 27%) in response to exercise and alcohol (509 +/- 98 v 724 +/- 109 mmol x L(-1) x 240 min; P = .03). Similar serum insulin response areas were obtained. After exercise and alcohol, plasma lactate increased compared with the resting state (2.2 +/- 0.2 v 1.6 +/- 0.1 mmol x L(-1), P = .004) and with exercise alone (2.2 +/- 0.2 v 1.8 +/- 0.2 mmol x L(-1), P = .04). Serum NEFAs were significantly reduced by exercise and alcohol compared with the resting state (0.50 +/- 0.04 v 0.65 +/- 0.06 mmol x L(-1), P = .008) and with exercise alone (0.50 +/- 0.04 v 0.61 +/- 0.05 mmol x L(-1), P = .02). Similar serum triglycerides were found. During the fasting state (part 2), similar plasma glucose response areas were obtained in the four situations. The insulin response area to exercise and alcohol increased significantly compared with the resting state (3,325 +/- 744 v 882 +/- 295 pmol x L(-1) x 240 min, P = .02) and with exercise alone (3,325 +/- 744 v 1,328 +/- 422 pmol x L(-1) x 240 min, P = .007). No difference was found compared with alcohol alone. Plasma lactate was higher after alcohol intake versus the resting state (1.9 +/- 0.1 v 1.3 +/- 0.1 mmol x L(-1), P = .003), as well as after exercise and alcohol (1.9 +/- 0.1 v 1.3 +/- 0.1 mmol x L(-1), P = .01). After exercise and alcohol serum NEFAs were significantly reduced compared with the resting state (0.43 +/- 0.02 v 0.64 +/- 0.02 mmol x L(-1), P < .001), alcohol alone (0.43 +/- 0.02 v 0.51 +/- 0.02 mmol x L(-1), P < .001), and exercise alone (0.43 +/- 0.02 v 0.64 +/- 0.02 mmol x L(-1), P < .001). Serum triglycerides were similar in the four situations. We conclude that moderate exercise with or without moderate alcohol intake does not cause acute hypoglycemia either after a light meal or in the fasting state in untrained overweight type 2 diabetic subjects.

Aerobic circuit exercise training: effect on adolescents with well-controlled insulin-dependent diabetes mellitus

OBJECTIVES

To test the safety and effects of exercise conditioning on cardiorespiratory fitness, body composition, muscle strength, glucose regulation, and lipid/cholesterol levels.

SUBJECTS

Ten male adolescents with insulin-dependent diabetes mellitus (IDDM) and 10 adolescent nondiabetic (ND) subjects.

DESIGN

Pretest, posttest intervention trial with control group.

SETTING

University-based human performance laboratory.

INTERVENTION

Mixed endurance and calisthenic/strength activities performed at a rapid pace three times weekly for 12 weeks.

RESULTS

Only one subject with IDDM experienced hypoglycemia after a single exercise session. Both subject groups improved their cardiorespiratory endurance (p < .05). Lean body mass of IDDM subjects increased by 3.5% (p < .05). Subjects with and without IDDM lowered their percent body fat (p < .05 and .001, respectively). Strength improvement of IDDM subjects ranged from 13.7% (p < .001) to 44.4% (p < .01), depending upon the maneuver. Fasting blood plasma glucose for all subjects was unchanged by training, but glycosylated hemoglobin A1c of IDDM subjects was reduced by .96 percentage point (p < .05). Reductions of HbA1c benefitted subjects exhibiting poor preconditioning glycemic control. Low-density lipoprotein cholesterol was decreased in subjects with IDDM (p < .05), but not total cholesterol or triglycerides.

CONCLUSION

Adolescents with IDDM undergoing aerobic circuit training improve their cardiorespiratory endurance, muscle strength, lipid profile, and glucose regulation. Aerobic circuit training is safe for properly trained and monitored adolescent diabetics.

Risk factors for cardiovascular disease in children with type I diabetes: Part II

Diabetes is a major risk factor for premature morbidity and mortality caused by cardiovascular disease (CVD). In Part I of this two part series, physiologic risk factors for cardiovascular disease in children with diabetes were presented. In Part II lifestyle CVD risk factors in children with diabetes will be discussed. Dietary factors, smoking behavior, and activity level are the risk factors most amenable to intervention. Two case studies are included to show clinical application of the data presented.

Oral glucose ingestion increases endurance capacity in normal and diabetic (type I) humans

The effects of an oral glucose administration (1 g/kg) 30 min before exercise on endurance capacity and metabolic responses were studied in 21 type I diabetic patients [insulin-dependent diabetes mellitus (IDDM)] and 23 normal controls (Con). Cycle ergometer exercise (55-60% of maximal O2 uptake) was performed until exhaustion. Glucose administration significantly increased endurance capacity in Con (112 +/- 7 vs. 125 +/- 6 min, P < 0.05) but only in IDDM patients whose blood glucose decreased during exercise (70.8 +/- 8.2 vs. 82.8 +/- 9.4 min, P < 0.05). Hyperglycemia was normalized at 15 min of exercise in Con (7.4 +/- 0.2 vs. 4.8 +/- 0.2 mM) but not in IDDM patients (12.4 +/- 0.7 vs. 15.6 +/- 0.9 mM). In Con, insulin and C-peptide levels were normalized during exercise. Glucose administration decreased growth hormone levels in both groups. In conclusion, oral glucose ingestion 30 min before exercise increases endurance capacity in Con and in some IDDM patients. In IDDM patients, in contrast with Con, exercise to exhaustion attenuates hyperglycemia but does not bring blood glucose levels to preglucose levels.

Influence of moderate physical exercise on insulin-mediated and non-insulin-mediated glucose uptake in healthy subjects

To establish the relative importance of insulin sensitivity and glucose effectiveness during exercise using Bergman's minimal model, 12 nontrained healthy subjects were studied at rest and during 95 minutes of moderate exercise (50% maximum oxygen consumption [VO2max]). Each subject underwent two frequently sampled intravenous glucose tolerance tests (FSIGTs) for 90 minutes, at rest (FSIGTr) and during exercise (FSIGTe). Plasma glucose, insulin, and C-peptide were determined. Insulin sensitivity (S(I)), glucose effectiveness at basal insulin (S(G)), insulin action [X(t)], and first-phase (phi1) and second-phase (phi2) beta-cell responsiveness to glucose were estimated using both minimal models of glucose disposal (MMg) and insulin kinetics (MMi). Glucose effectiveness at zero insulin (GEZI), glucose tolerance index (K(G)), and the area under the insulin curve (AUC(0-90)) were also calculated. Intravenous glucose tolerance improved significantly during physical exercise. During exercise, S(I) (FSIGTr v FSIGTe: 8.5 +/- 1.0 v 25.5 +/- 7.2 x 10(-5) x min(-1) [pmol x L(-1)]-1, P < .01), S(G) (0.195 +/- 0.03 v 0.283 +/- 0.03 x 10(-1) x min(-1), P < .05), and GEZI (0.190 +/- 0.03 v 0.269 +/- 0.04 x 10(-1) x min(-1), P < .05) increased; however, no changes in phi1 and phi2 were found. Despite a significant decrease in the insulin response to glucose (AUC0-90, 21,000 +/- 2,008 v 14,340 +/- 2,596 pmol x L(-1) x min, P < .01), insulin action [X(t)] was significantly higher during the FSIGTe. These results show that physical exercise improves mainly insulin sensitivity, and to a lesser degree, glucose effectiveness. During exercise, the insulin response to glucose was lower than at rest, but beta-cell responsiveness to glucose did not change.

Fat cells

The adipocyte is a metabolically active cell that functions to store energy for times of energy deprivation or enhanced need. Obesity is characterized by increased lipid accumulation and turnover compared with the nonobese state. Both triglyceride synthesis and lipolysis are regulated metabolic processes in the adipocyte. Current research on the metabolic activities of the human adipocyte focus on plasma triglyceride hydrolysis and uptake of fatty acids by LPL, esterification of these fatty acids, and the subsequent triglyceride breakdown by hormone-sensitive lipase in response to stimulation of adrenergic receptors. These topics are discussed in relationship to the development of obesity.

Exercise tolerance is lower in type I diabetics compared with normal young men

The present investigation was conducted to study metabolic and hormonal responses to prolonged exercise to exhaustion in insulin-dependent diabetic subjects. Sixteen healthy subjects (control) and 15 diabetics with no-insulin administration for 12 hours were studied. They were submitted to short-term exercise to exhaustion on a cycle ergometer at 55% to 60% of maximum oxygen consumption (VO2max). Exercise tolerance was significantly lower in diabetic subjects (66 +/- 6.7 v 117 +/- 9.4 minutes), and glucose concentration was significantly higher in these subjects. At exhaustion, only diabetic subjects showed a significant decrease in glycemia (142 +/- 20 v 111 +/- 16 mg/dL). Lactate concentration increased significantly during exercise up to 30 minutes, but at exhaustion only control subjects showed a reduction. No significant difference in free fatty acid (FFA) concentrations was observed between the groups during a 30-minute exercise period; however, at exhaustion levels were significantly higher in control subjects. Prolactin and C-peptide concentrations were significantly lower in diabetic subjects, whereas glucagon concentration was higher. No significant differences between the groups were observed for cortisol and growth hormone (GH) concentrations. We conclude that (1) diabetic subjects show reduced exercise tolerance when no insulin is administered for 12 hours, and (2) exercise to exhaustion reduces serum glucose concentrations in insulin-dependent diabetics.

Plasma glucose metabolism during exercise in humans

Plasma glucose is an important energy source in exercising humans, supplying between 20 and 50% of the total oxidative energy production and between 25 and 100% of the total carbohydrate oxidised during submaximal exercise. Plasma glucose utilisation increases with the intensity of exercise, due to an increase in glucose utilisation by each active muscle fibre, an increase in the number of active muscle fibres, or both. Plasma glucose utilisation also increases with the duration of exercise, thereby partially compensating for the progressive decrease in muscle glycogen concentration. When compared at the same absolute exercise intensity (i.e. the same VO2), reliance on plasma glucose is also greater during exercise performed with a small muscle mass, i.e. with the arms or just 1 leg. This may be due to differences in the relative exercise intensity (i.e. the %VO2peak), or due to differences between the arms and legs in their fitness for aerobic activity. The rate of plasma glucose utilisation is decreased when plasma free fatty acid or muscle glycogen concentrations are very high, effects which are probably mediated by increases in muscle glucose-6-phosphate concentration. However, glucose utilisation is also reduced during exercise following a low carbohydrate diet, despite the fact that muscle glycogen is also often lower. When exercise is performed at the same absolute intensity before and after endurance training, plasma glucose utilisation is lower in the trained state. During exercise performed at the same relative intensity, however, glucose utilisation may be lower, the same, or actually higher in trained than in untrained subjects, because of the greater absolute VO2 and demand for substrate in trained subjects during exercise at a given relative exercise intensity. Although both hyperglycaemia and hypoglycaemia may occur during exercise, plasma glucose concentration usually remains relatively constant. Factors which increase or decrease the reliance of peripheral tissues on plasma glucose during exercise are therefore generally accompanied by quantitatively similar increases or decreases in glucose production. These changes in total glucose production are mediated by changes in both hepatic glycogenolysis and hepatic gluconeogenesis. Glycogenolysis dominates under most conditions, and is greatest early in exercise, during high intensity exercise, or when dietary carbohydrate intake is high. The rate of gluconeogenesis is increased when exercise is prolonged, preceded by a restricted carbohydrate intake, or performed with the arms. Both glycogenolysis and gluconeogenesis appear to be decreased by endurance exercise training. These effects are due to changes in both the hormonal milieu and in the availability of hepatic glycogen and gluconeogenic precursors.(ABSTRACT TRUNCATED AT 400 WORDS)

Exercise and diabetes mellitus

As more is understood about the physiology of exercise, both in normal and in diabetic subjects, its role in the treatment of diabetes is becoming better defined. Although persons with diabetes may derive many benefits from regular physical exercise, there also are a number of hazards that make exercise difficult to manage. In insulin-treated diabetics, there are risks of hypoglycemia during or after exercise or of worsening metabolic control if insulin deficiency is present. Type II diabetics being treated with sulfonylureas also are at some increased risk of developing hypoglycemia during or following exercise, although this is less of a problem than occurs with insulin treatment. In individuals treated by diet alone, regulation of blood glucose during exercise usually results in a decrease in glucose concentration toward normal but not to hypoglycemic levels and exercise can be used safely as an adjunct to diet to achieve weight loss and improved insulin sensitivity. When obese patients with type II diabetes are treated with very low calorie diets, adequate amounts of carbohydrate must be provided to ensure maintenance of normal muscle glycogen content, particularly if individuals wish to participate in high intensity exercise that places a heavy workload on specific muscle groups. On the other hand, moderate intensity exercise such as vigorous walking can be tolerated by individuals on very low calorie, carbohydrate-restricted diets after an appropriate period of adaptation. A number of strategies can be employed to avoid hypoglycemia in patients with insulin-treated diabetes and both type I and type II diabetic subjects should be examined carefully for long term complications of their disease, which may be worsened by exercise. These considerations have led many diabetologists to consider exercise to be beneficial in the management of diabetes for some individuals but not to be recommended for everyone as a "necessary" part of diabetic treatment as was thought in the past. Instead, the goals should be to teach patients to incorporate exercise into their daily lives if they wish and to develop strategies to avoid the complications of exercise. The rationale for the use of exercise as part of the treatment program in type II diabetes is much clearer and regular exercise may be prescribed as an adjunct to caloric restriction for weight reduction and as a means of improving insulin sensitivity in the obese, insulin-resistant individual.

Metabolic response to exercise in dialysis patients

The metabolic and hormonal response to acute moderate intensity (40% of VO2 max) bicycle exercise was examined in eight uremic subjects maintained on chronic dialysis and in 12 age- and weight-matched controls before and after the administration of low dose, selective (metoprolol) and nonselective (propranolol), beta adrenergic antagonists. The fasting plasma glucose concentration and basal rates of hepatic glucose production (HGP) and tissue glucose disappearance (Rd) were similar in control and uremic subjects. In both groups HGP and Rd increased in parallel during exercise, and the plasma glucose concentration remained constant at the fasting level. However, the increments in Rd (2.27 +/- 0.27 vs. 0.87 +/- 0.31 mg/kg.min, P less than 0.01) and HGP (2.47 +/- 0.22 vs. 0.92 +/- 0.19 mg/kg.min, P less than 0.01) were 2.5-3 fold greater in the control compared to uremic subjects. Although the VO2max was decreased by 50% (39 +/- 2 vs. 20 +/- 2 ml/min.kg; P less than 0.01), the correlation between Rd and VO2max was weak (r = 0.33, P less than 0.10), suggesting that factors other than diminished physical fitness contribute to diminished tissue uptake of glucose in the dialyzed uremic patients. Following the cessation of exercise, HGP and Rd promptly returned toward basal levels in both uremic and control subjects. The glucose homeostatic response to exercise was not significantly altered by either propranolol or metoprolol. In the postabsorptive state fasting levels of insulin, glucagon, epinephrine, and norepinephrine all were significantly increased in the uremic group (P less than 0.01 to 0.05). During exercise in the healthy young controls the plasma insulin concentration declined and plasma epinephrine and norepinephrine levels rose three- to fourfold. In contrast, in uremics plasma insulin failed to fall (P less than 0.05) and the increase in circulating epinephrine and norepinephrine levels was markedly impaired (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)