Metabolic and hormonal effects of muscular exercise in juvenile type diabetics

The adjustment of diet and insulin dose during long-term endurance exercise in type 1 (insulin-dependent) diabetic men

We examined in 2 consecutive years the effect of a 75-km (greater than 7 h) cross country skiing on dietary and insulin requirements and glycaemic control in 9 Type 1 (insulin-dependent) diabetic patients. In the first year, the patients were hyperglycaemic (20.9 +/- 1.8 mmol/l) before the race due to excessive carbohydrate loading (65 g) and reduction (by 58%) of short-acting insulin for breakfast. In the second year, breakfast included less carbohydrate (40 g) and more protein, and the morning short-acting insulin was reduced by 35%. With this adjustment of therapy the pre-exercise hyperglycaemia was less (p less than 0.05). The morning intermediate-acting insulin was reduced by 28 and 38% in consecutive years. During both races carbohydrate intake approximated 40 g/h, and blood glucose was maintained at near normal levels after 33 km of skiing. Hypoglycaemia did not occur during exercise, but one patient had symptomatic hypoglycaemia after finishing the second race. The day after exercise insulin sensitivity was increased in all four patients studied. Insulin treated patients can perform strenuous long-term exercise and maintain near normoglycaemia with a proper adjustment of therapy. Augmented insulin sensitivity may contribute to post-exercise hypoglycaemia.

Abnormal glucoregulation during exercise in type II (non-insulin-dependent) diabetes

We studied the effects of exercise on the levels of plasma glucose and glucoregulatory hormones before and after 6 weeks of thrice-weekly physical training in 20 sedentary type II (non-insulin-dependent) diabetic patients and 11 control subjects matched for previous physical activity. Parameters were measured at rest, after 30 minutes of bicycle exercise at 70% to 75% of maximal oxygen uptake, and after 30 minutes of recovery. In the untrained state exercise resulted in a decrease in plasma glucose levels in diabetics but not in controls (-12 +/- 5 v + 4 +/- 2 mg/dL, P less than .01) and the expected drop in plasma insulin level was absent in diabetics. These differences in glucose and insulin response persisted after physical training. There was a tendency for patients with diabetes to have a smaller R-R interval variation during deep breathing, an abnormal resting heart rate response to physical training, and a lesser increment in plasma epinephrine levels following exercise, findings consistent with autonomic dysfunction. Physical training resulted in a blunting of the exercise-induced increment of plasma epinephrine, growth hormone, and lactate levels in control subjects, but not in diabetics. Our data demonstrate a hypoglycemic effect of exercise in mildly hyperglycemic nonobese type II diabetics. Possible causative factors include: hyperglycemia per se, a lack of physiologic suppression of plasma insulin, and abnormalities of autonomic or hypothalamic regulatory function.

Postprandial walking exercise in pregnant insulin-dependent (type I) diabetic women: reduction of plasma lipid levels but absence of a significant effect on glycemic control

In this study 42 pregnant women with type I diabetes and 28 nondiabetic controls were recruited to participate in a postprandial walking exercise program. Exercise patients were instructed to walk 20 minutes (1 mile) after each meal and were divided into two groups: group 1 were normal nondiabetic controls and group 2 were women with type I diabetes. There were two nonexercise comparison groups: group 3, nondiabetic controls, and group 4, women with type I diabetes. Diabetic women were followed weekly in an intensive perinatal program. Glycemic control was assessed by serial hemoglobin A1 concentration measurements, home blood glucose monitoring, 24-hour glucose profiles, and 24-hour quantitative urinary glucose loss. Glycemic control was modestly but not significantly superior in the diabetic exercise group 2 compared with the diabetic nonexercise group 4. Exercise was associated with lower fasting cholesterol and triglyceride values in both controls and diabetic women, with significantly lower fasting plasma triglyceride levels in the diabetic exercise group (p less than 0.02). There were no adverse effects of postprandial walking exercise in mothers or infants.

Effects of dynamic exercise and metabolic control on left ventricular performance in insulin-dependent diabetes mellitus

In subclinical diabetic cardiomyopathy, previous reports did not positively correlate the altered cardiac performance with metabolic parameters. Fifteen insulin-dependent diabetic subjects, without any clinical or instrumental evidence of heart diseases, were studied. Signs of diabetic microangiopathy were absent. Systolic time intervals, metabolic and hormonal parameters (blood glucose, free fatty acids, blood lactate and plasma norepinephrine) were evaluated at rest and after dynamic exercise during poor (MAGE 6.36 +/- 0.72 mmol/l) and good (MAGE 3.46 +/- 0.66 mmol/l) metabolic control, obtained by means of insulin therapy. Rest values of systolic time intervals were normal during poor and good metabolic control. After exercise, pre-ejection period/left ventricular ejection time ratio increased mainly during poor control as a result of an increased pre-ejection period: conversely, a smaller increase in pre-ejection period/left ventricular ejection time ratio occurred during good metabolic control. The exercise induced free fatty acids utilization did not occur during poor control as it occurred during good control. The percentage of increments in blood lactate was virtually identical in ketotic and non-ketotic patients and in normal subjects. High norepinephrine plasma levels were observed both at rest and during dynamic exercise in poorly controlled diabetic patients. Conclusively, testing of systolic time intervals after exercise might be useful in the detection of preclinical diabetic cardiomyopathy. The decreased cardiac functional reserve observed during poor control might be related to an altered energetic fuel utilization.

Mechanism of the hyperketonaemic effect of prolonged exercise in insulin-deprived type 1 (insulin-dependent) diabetic patients

The effects of moderate exercise of 2-h duration on the concentration and turnover rate of total ketone bodies were assessed in 7 acutely insulin-deprived Type 1 (insulin-dependent) diabetic patients with an isotope tracer technique using a constant infusion of 14C-beta-hydroxybutyrate. These results were compared to those obtained in 13 normal control subjects in whom a similar range of hyperketonaemia (approximately 1-6 mmol/l) was induced by fasting. In all subjects, the concentration and the rate of production of ketone bodies followed a biphasic pattern with an initial fall lasting for about 20 min followed by a secondary rise. When integrated over the entire working period, the exercise-induced changes in ketone turnover were markedly dependent on the initial ketone body concentrations in both groups: at low ketonaemia (approximately 1 mmol/l), exercise increased the rate of production and disposal of ketones. These effects were progressively attenuated as basal ketonaemia rose and were reversed to an inhibitory action in markedly ketotic subjects (greater than 4 mmol/l). Despite the finding that, at high ketosis, exercise inhibited ketogenesis to a similar degree in control subjects and diabetic patients, the changes in concentration recorded at the end of exercise were different in the 2 groups: ketonaemia was reduced in fasted control subjects and increased in the diabetic patients. These data suggest that, contrary to a widely accepted opinion, the hyperketonaemic effect of prolonged exercise in ketotic diabetic patients does not result from an exaggerated stimulation of ketogenesis, but from some defect in their removal capacities for ketones, possibly related to insulinopenia.

The roles of diet and exercise in the management of patients with insulin-dependent diabetes mellitus

Current dietary recommendations for patients with diabetes are similar to those for the US population in general, including a moderate intake of sucrose. Awareness of the carbohydrate content of meals will allow adjustments of the dose of meal-related short-acting insulin when the size of the meal is altered; thus, meal planning can be flexible without sacrificing glycemic control. Although exercise may have potential benefits for patients with diabetes, it is also associated with greater risk in these persons than in their nondiabetic counterparts and frequently complicates the management of their disease. If there are no contraindications to regular, vigorous exercise and the patient desires to participate, careful self-monitoring of blood glucose, combined with snacks and insulin dose adjustment, should enable the intensively treated patient to exercise safely.

Influence of metabolic control of insulin-dependent diabetes on plasma nucleotide levels (cAMP, cGMP) during bicycle exercise

Plasma concentrations of cyclic nucleotides (cAMP, cGMP) were measured before and during bicycle exercise in 8 well-controlled (mean pre-exercise blood glucose 5.3 mmol/l; HbA1 8.6%) and 8 moderately controlled (mean pre-exercise blood glucose 12.2 mmol/l; HbA1 10.8%) patients aged 18-32 years with insulin-dependent diabetes mellitus (IDDM) and in a group of non-diabetic control subjects matched for age and sex. Pre-exercise plasma cAMP concentrations and the rise with exercise were similar in all study groups. Significantly lower resting cGMP levels were found in well-controlled IDDM patients (3.5 +/- 0.3 pmol/ml, mean +/- SEM) compared to controls (5.6 +/- 1.1 pmol/ml; p less than 0.05) and moderately controlled IDDM patients (5.6 +/- 1.0 pmol/ml; p less than 0.05). By contrast, plasma cGMP levels increased during exercise in the diabetics but not in the controls. These findings indicate a significant difference in responses of plasma cGMP to exercise between IDDM patients and controls.

Diabetes, insulin and exercise

The metabolic and hormonal adaptations to single exercise sessions and to exercise training in normal man and in patients with insulin-dependent as well as non-insulin-dependent diabetes mellitus are reviewed. In insulin-dependent (type I) diabetes good metabolic control is best obtained by a regular pattern of life which will lead to a fairly constant demand for insulin from day to day. Exercise is by nature a perturbation that makes treatment of diabetes difficult: Muscle contractions per se tend to decrease the plasma glucose concentration whereas the exercise-induced response of the so-called counter-regulatory hormones tend to increase plasma glucose by increasing hepatic glucose production and adipose tissue lipolysis. If the pre-exercise plasma insulin level is high, hypoglycaemia may develop during exercise whereas hyperglycaemia and ketosis may develop if pre-exercise plasma insulin levels are low. Physical activity is often difficult to carry out on a precise schedule and the exercise-induced changes in demand for insulin and calories vary according to the intensity and duration of exercise, time of day, and differ within and between individuals. Thus, physical training can not be recommended as a means of improving metabolic control in insulin-dependent diabetes. However, our present knowledge and technology allows the well-informed and cooperative patient to exercise and even to reach the elite level. To achieve this, pre-exercise metabolic control should be optimal and knowledge of the patient's reaction to exercise is desirable, which necessitates frequent self-monitoring of plasma glucose. It may often be necessary to diminish the insulin dose before exercise, and/or to ingest additional carbohydrate during or after exercise. In non-insulin-dependent (type II) diabetes, exercise is associated with less risk of metabolic derangement, and in genetically disposed individuals physical training may prevent development of overt diabetes possibly by diminishing the strain on the pancreatic beta cell. The latter, however, is only achieved if exercise is not accompanied by increased caloric intake. Whether physical training in diabetes can reduce cardiovascular morbidity and mortality is at present unknown, but training has in diabetic patients been shown to lessen some risk factors for development of arteriosclerosis. However, training of diabetics (especially in the less well-regulated patient) may not lessen coronary risk factors to the same extent as in healthy subjects.

Psychological stress and metabolic control in patients with type I diabetes mellitus

Acute psychological stress is believed to cause disturbances of metabolic control in patients with Type I diabetes. To examine the validity of this assumption, we subjected nine healthy persons (mean [+/- SEM] blood glucose level, 74 +/- 2 mg per deciliter), nine patients with Type I diabetes who had normoglycemia (130 +/- 10 mg per deciliter), and nine diabetic patients with hyperglycemia (444 +/- 17 mg per deciliter) to two acute psychological stresses: mental arithmetic and public speaking. Subjects in the three groups were matched for age, weight, sex, and socioeconomic status. For all subjects, the mean increase in heart rate was 20 beats per minute while they were doing mental arithmetic and 25 beats per minute while they were speaking publicly (P less than 0.001). In all three groups, systolic and diastolic pressure rose markedly, the plasma epinephrine level increased by 50 to 150 pg per milliliter, and the norepinephrine level by 100 to 200 pg per milliliter under both stress conditions (P less than 0.001). The plasma cortisol level rose significantly after public speaking in all groups. Neither stress induced changes in circulating levels of glucose, ketones, free fatty acids, glucagon, or growth hormone. Thus, sudden, short-lived psychological stimuli causing marked cardiovascular responses and moderate elevations in plasma concentrations of catecholamines and cortisol are unlikely to disturb metabolic control in patients with Type I diabetes.

Interaction between insulin and counterregulatory hormones in control of substrate utilization in health and diabetes during exercise

In summary, the appropriate balance of glucagon and insulin at the liver and the catecholamines and insulin in the periphery provide the most optimal balance of substrate fluxes to the working muscle. When the hormonal balance is perturbed such as is seen in diabetes or with glucagon suppression, or when the effect of a hormone is impaired such as with beta blockade, optimal substrate balance is lost. The effects of these hormones can be overridden by metabolic factors in muscle, as evidenced by the uncoupling of the normal catecholamine antagonism of glucose uptake from the actual glucose uptake observed during exercise under conditions of tissue hypoxia.

Physical training and insulin sensitivity

In conclusion, a large body of available evidence indicates that the degree of physical conditioning is an important determinant of insulin sensitivity and overall glucose tolerance. Both acute exercise and chronic physical training are associated with enhanced disposal of a glucose load. Conversely, physical inactivity leads to a deterioration in glucose tolerance. The primary tissue responsible for accelerated glucose disposal following exercise is muscle. After an acute bout of exercise, enhanced glucose transport and augmented glycogen synthesis are largely responsible for the improvement in glucose tolerance. The beneficial effects of chronic physical training on glucose metabolism appear to be explained by multiple factors, including increased muscle mass, augmented muscle blood flow and capillary area, enhanced mitochondrial oxidative enzyme capacity, and activation of the glucose transport system. Despite these well-documented effects of training on glucose metabolism, the precise role of exercise in the treatment of diabetic patients remains to be established. In insulin-dependent (type I) diabetic individuals, acute exercise has been shown to be a helpful adjunct in establishing good glycemic control. However, the role of acute exercise in helping to smooth out glycemic control in non-insulin-dependent (type II) diabetic patients has received little attention. The role of chronic physical training in the treatment of both insulin-dependent (type I) and non-insulin-dependent (type II) diabetic individuals remains to be established.

Hormonal and metabolic response to three types of exercise of equal duration and external work output

Five normal men, aged 20-30 years, participated in three types of exercise (I, II, III) of equal duration (20 min) and total external work output (120-180 kJ) separated by ten days of rest. Exercises consisted of seven sets of squats with barbells on the shoulders (I; Maximal Power Output Wmax = 600-900 W), continuous cycling at 50 rev X min-1 (II; Wmax = 100-150 W) and seven bouts of intermittent cycling at 70 rev X min-1 (III; Wmax = 300-450 W). Plasma cortisol, glucagon and lactate increased significantly (P less than 0.05) during the exercise and recovery periods of the anaerobic, intermittent exercise (I and III) but not in the continuous, aerobic exercise (II). No consistent significant changes were found in plasma glucose. Plasma insulin levels decreased only during exercise II. The highest increase in cortisol and glucagon was not associated with the highest VE, VO2, Wmax or HR; however it was associated with the anaerobic component of exercise (lactic acid). It is suggested that in exercises of equal duration and total external work output, the continuous, aerobic exercise (II) led to lowest levels of glucogenic hormones.

Metabolic response to different forms of physical exercise in type I diabetics and the duration of the glucose lowering effect

In order to analyse the metabolic effect of exercise nine well-controlled type I diabetics took part in four series of tests: (i) a short exercise with maximal work load, (ii) a 30 min exercise with half maximal work load, (iii) a 3 x 10 min interval exercise and (iv) control without exercise. Exercises were performed on a bicycle ergometer starting at 09.00 h. On the test days, only two thirds of the normal insulin dose was given. Blood glucose, free insulin, glucagon, catecholamines, growth hormone, cortisol, lactate and pyruvate were measured during the exercise and the following 60 min. Glucose profiles were taken until 17.15 h. The short exercise with maximal work load did not affect blood glucose, the half maximal exercise and the interval exercise resulted in a decrease. Short rest phases did not modify the glucose lowering effect nor the overall response of counterregulatory hormones. A snack following exercise resulted in a total compensation of the glucose lowering effect.

Metabolic responses to physical training in young insulin-dependent diabetics

Insulin-dependent (type 1) diabetics, aged 14-17 years, were studied according to two protocols. During a 6-month training period of moderate intensity (six participants) the aerobic work capacity and the erythrocyte insulin binding increased by 19% and 28%, respectively. Glycosylated haemoglobin (HbA1) was not significantly reduced. A 2-week intensive physical training program (10 participants) was associated with a 50% decrease of blood glucose values, which did not last beyond the training period. Plasma ketone bodies were markedly reduced. We conclude that young type 1 diabetics may participate in strenuous, short-term physical training. The improved aerobic work capacity and increased cellular insulin binding observed during training of moderate intensity is of potential benefit in the long-term management of the patients.

Hormonal regulation of glucose transport in contracting skeletal muscle from normal and diabetic rats

Using the hindlimb perfusion system, we have studied glycogenolysis and glucose transport in resting and contracting skeletal muscle from normal and diabetic rats. Glucose transport was measured using the glucose analogue 2-deoxyglucose. The muscles were treated for 15 minutes with either saline solution, insulin (1 mU/mL) or epinephrine (10(-7) mol/L) at rest and during electrical stimulation. In the resting muscle, basal glycogen was lower in diabetic rats (25 v 40 mumol/g), was not affected by insulin in either group, and was decreased by epinephrine in normal rats (to 26 mumol/g) but not in diabetic rats. Basal glucose transport was identical in the two groups (7.5 mumol/100 g/minute), was stimulated by insulin to a greater extent in diabetics (fivefold) than in normal rats (threefold), but was unaffected by epinephrine in either group. In contracting muscle, glycogen was decreased by 10 mumol/g in normal and diabetic rats independently of hormonal treatment. Basal glucose transport was not affected by muscle contraction with or without epinephrine, whereas the stimulatory effect of insulin on this process was blunted by such contraction (result, 10 mumoles/100 g/minute). We conclude that in normal and diabetic rats, muscle contraction stimulates glycogen breakdown independently of hormonal treatment; muscle contraction per se does not increase glucose transport; and finally, contracting muscle uses glycogen rather than circulating glucose as energy substrate.

Decrease in ventricular beta-adrenergic receptors in trained diabetic rats

The effects of physical training on beta-adrenergic receptors were evaluated in heart ventricular tissue of diabetic rats. Mild diabetes mellitus was induced in rats with streptozotocin (45 mg/kg, iv). They were then submitted to a progressive 10-week running programme on a treadmill. Binding studies were done at six different concentrations of (-) [3H]dihydroalprenolol (0.5 to 14.4 nM) with ventricular membrane preparations from control (n = 13), sedentary diabetic (n = 9) and trained diabetic rats (n = 10). Direct linear plot analysis of the data revealed that the total number of beta-adrenoceptors was reduced in sedentary diabetic rats as compared to control (2231 +/- 207 vs 2922 +/- 211 fmol/ventricles; P less than 0.05); however, there was no significant change in the receptor density expressed as fmol/mg of membrane protein (40 +/- 3 vs 43 +/- 3; P greater than 0.05). On the other hand, the beta-adrenergic binding sites were decreased in training diabetic rats, either expressed as the total number of receptors (1920 +/- 179 vs 2922 +/- 211; P less than 0.01), or as fmol/mg of membrane protein (30 +/- 3 vs 43 +/- 3; P less than 0.01). There was no significant change in the dissociation constant (KD) of these receptors between groups (KD = 4.08 +/- 0.51, 4.69 +/- 0.93 and 2.88 +/- 0.39 nM respectively for control, sedentary diabetic and diabetic trained animals). The basal epinephrine concentration was significantly increased in trained diabetic rats (102 +/- 21 pg/ml vs 47 +/- 7 for control (P less than 0.05) and vs 49 +/- 9 for sedentary diabetic (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Turnover and splanchnic metabolism of free fatty acids and ketones in insulin-dependent diabetics at rest and in response to exercise

Nine insulin-dependent diabetics and six healthy controls were studied at rest, during, and after 60 min of bicycle exercise at a work load corresponding to 45% of their maximal oxygen intake. The catheter technique was employed to determine splanchnic and leg exchange of metabolites. FFA turnover and regional exchange was evaluated using [14C]oleate infusion. Basal glucose (13.8 +/- 1.1 mmol/l), ketone body (1.12 +/- 0.12 mmol/l), and FFA (967 +/- 110 mumol/l) concentrations were elevated in the diabetics in comparison with controls. In the resting state, splanchnic ketone acid production in the diabetics was 6-10-fold greater than in controls. Uptake of oleic acid by the splanchnic bed was increased 2-3-fold, and the proportion of splanchnic FFA uptake converted to ketones (61%) was threefold greater than in controls. In contrast, splanchnic fractional extraction of oleic acid was identical in diabetics and controls. A direct relationship was observed between splanchnic uptake and splanchnic inflow (plasma concentration X hepatic plasma flow) of oleic acid that could be described by the same regression line in the diabetic and control groups. During exercise, splanchnic ketone production rose in both groups. In the control group the increase in ketogenesis was associated with a rise in splanchnic inflow and in uptake of oleic acid, a rise in splanchnic fractional extraction of oleate, and an increase in the proportion of splanchnic FFA uptake converted to ketone acids from 20-40%. In the diabetic group, the increase in ketogenesis occurred in the absence of a rise in splanchnic inflow or uptake of oleic acid, but was associated with an increase in splanchnic fractional extraction of oleic acid and a marked increase in hepatic conversion of FFA to ketones, so that the entire uptake of FFA was accountable as ketone acid output. Splanchnic uptake of oleic acid correlated directly with splanchnic oleic acid inflow in both groups, but the slope of the regression line was steeper than in the resting state. Plasma glucagon levels were higher in the diabetic group at rest and during exercise, while plasma norepinephrine showed a twofold greater increment in response to exercise in the diabetic group (to 1,400-1,500 pg/ml). A net uptake of ketone acids by the leg was observed during exercise but could account for less than 5% of leg oxidative metabolism in the diabetics and less than 1% in controls. Despite the increase in ketogenesis during exercise, a rise in arterial ketone acid levels was not observed in the diabetics until postexercise recovery, during which sustained increments to values of 1.8-1.9 mmol/l and sustained increases in splanchnic ketone production were observed at 30-60 min. The largest increment in blood ketone acids and in splanchnic ketone production above values observed in controls thus occurred in the diabetics after 60 min of recovery from exercise. We concluded that: (a) In the resting state, increased ketogenesis in the diabetic is a consequence of augmented splanchnic inflow of FFA and increased intrahepatic conversion of FFA to ketones, but does not depend on augmented fractional extraction of circulating FFA by the splanchnic bed. (b) Exercise-induced increases in ketogenesis in normal subjects are due to augmented splanchnic inflow and fractional extraction of FFA as well as increased intrahepatic conversion of FFA to ketones. (c) When exercise and diabetes are combined, ketogenesis increases further despite the absence of a rise in splanchnic inflow of FFA. An increase in splanchnic fractional extraction of FFA and a marked increase intrahepatic conversion of FFA to ketones accounts for the exaggerated ketogenic response to exercise in the diabetic. (d) Elevated levels of plasma glucagon and/or norepinephrine may account for the increased hepatic ketogenic response to exercise in the diabetic. (e) Ketone utilization by muscle increases during exercise but constitutes a quantitatively minor oxidative fuel for muscle even in the diabetic. (f) The accelerated ketogenesis during exercise in the diabetic continues unabated during the recovery period, resulting in an exaggerated postexercise ketosis.

Studies on the mechanism of improved glucose control during regular exercise in type 2 (non-insulin-dependent) diabetes

The effects of 6 weeks of thrice weekly training on glycaemic control were assessed in 20 sedentary Type 2 (non-insulin-dependent) diabetic patients and 11 control subjects matched for previous physical activity. Maximal oxygen uptake was lower in the diabetic patients than in control subjects before training (26.2 +/- 1.1 versus 32.6 +-/ 1.7 ml X kg-1 X min-1; p less than 0.001). Glycosylated haemoglobin levels decreased in the diabetic patients during the training programme (12.2 +/- 0.5 to 10.7 +/- 0.4%; p less than 0.02). Oral and intravenous glucose tolerance determined 72 h after the last exercise period showed only minimal improvement. Plasma glucose levels were, however, significantly lower at 12 h than 72 h after exercise in eight subjects tested at both time points. These data suggest than an exercise programme can produce a significant decrease in glycosylated haemoglobin levels in Type 2 diabetic males probably due, in great measure, to the cumulative effect of transient improvements in glucose tolerance which follow each individual period of exercise.

Sensitive and simplified method for the differential determination of serum levels of ketone bodies

A highly sensitive and simplified method for the differential determination of serum ketone bodies has been developed. Serum was deproteinized with perchloric acid, and acetoacetate contained in the supernate was reacted with newly synthesized p-nitrobenzene diazonium fluoroborate at 37 degrees C for 10 min. The formed hydrazo compound was converted by alkali to the more stable azo compound which has a peak absorbance at 645 nm. For the determination of 3-hydroxybutyrate, this was enzymatically converted to acetoacetate using 3-hydroxybutyrate dehydrogenase, LDH, NAD and pyruvate. Using 0.2 ml serum, acetoacetate and 3-hydroxybutyrate could be quantitated in 30 min. The described method is five times more sensitive than the enzymatic photometric method and can detect individual ketone bodies at concentrations as low as 20 mumol/l. Differential determination of serum levels of ketone bodies is clinically useful for the diagnosis of type 1 diabetes and in monitoring diabetic control.

Absence of exercise-induced hypoglycaemia in type i (insulin-dependent) diabetic patients during maintenance of normoglycaemia by short-term, open-loop insulin infusion

To assess the risk and possible mechanisms of hypoglycaemia during moderate exercise in Type I (insulin-dependent) diabetic patients receiving constant insulin infusion, five insulin-dependent male diabetic patients were exercised 18 h after their last meal and 30 h after their last injection of intermediate acting insulin. Intravenous insulin was initially delivered via a closed-loop infusion system programmed to lower mean blood glucose from 11.3 +/- 1.8 to 4.8 +/- 0.4 mmol/l over approximately 3.5 h. Blood glucose was then maintained at this level for 4 h. At this time, the closed-loop infusion was discontinued and replaced by an open-loop system. The average amount of insulin infused per min during the 4 h normoglycaemic closed-loop period was calculated and this amount was infused at a constant rate during both a 30 min period of exercise on a bicycle ergometer (approximately 65% maximum oxygen uptake) and a 30 min rest period which followed. Five nondiabetic males served as control subjects. Despite significantly higher free insulin concentrations (p less than 0.05) and identical pre-exercise blood glucose concentrations, blood glucose rose during exercise only in the diabetic group (0.5 +/- 0.2 mmol/l; p less than 0.01). Changes in the serum concentrations of lactate, glycerol, glucagon, cortisol, non-esterified fatty acids and growth hormone were similar in the two groups and did not account for the increment of blood glucose in the diabetic patients. Beta-hydroxybutyrate concentrations were, however, higher in the diabetic patients at the onset of exercise (p less than 0.01) and decreased significantly more than the control subjects during exercise. We conclude that exercise under these conditions in diabetic patients is not attended by hypoglycaemia.

Effect of prolonged optimal blood sugar control by i.v. insulin administration on plasma free fatty acid and glycerol concentrations of insulin-dependent diabetics during exercise

Four type I diabetics were kept close to normoglycemic during a period of 1 month by means of a an open loop i.v. insulin infusion system (Siemens). During submaximal physical exercise their metabolic response was nearly normal. No hypoglycemic episodes during exercise were registered despite the fact that the regular basal infusion rate was not changed. The level of free fatty acids rose approximately to the same extent as in normal subjects. A slight inhibition of lipolysis during i.v. insulin therapy was apparent from the less marked rise of the glycerol levels. The feasibility of a simple open loop i.v. insulin regimen over a prolonged period of time is underscored by these results which show that the basal insulin infusion rate can be kept constant during exercise.

Metabolic response of normal man and insulin-infused diabetics to postprandial exercise

Physical exercise is often performed during absorption of meals. We have characterized the metabolic response to 45 min of moderate exercise (approximately 55% of estimated maximal oxygen uptake) beginning 30 min after breakfast in seven healthy controls. Nine insulin-dependent diabetes were studied in an identical manner, with glycemia controlled by a closed-loop "artificial endocrine pancreas" controlled by a closed-loop "artificial endocrine pancreas" (AEP). Responses were compared to those during breakfast without exercise. In the controls, onset of exercise rapidly reversed the rise in both glycemia and insulin (IRI) that occurred with breakfast alone, both returning to fasting levels (glycemia, 80 +/- 3 mg/dl; IRI, 0.38 +/- 0.10 ng/ml). After exercise, small and transient increments occurred (glycemia, 33 +/- 6 mg/dl; IRI, 0.81 +/- 0.15 ng/ml). In the diabetics, prior overnight intravenous insulin normalized fasting glycemia (98 +/- 4 mg/dl), and its postbreakfast excursion was identical to that of controls, as were those of most measured substrates. Similarly, with exercise, glycemia returned rapidly to fasting levels, accompanied by an appropriate decrease in insulin infusion rates. "Free" IRI levels mirrored changes in infusion rates by the AEP, with a decrease in insulin requirement of 30% during exercise as compared to breakfast alone (P less than 0.05). Thus, in both diabetics treated with the AEP and in normals, the responses to postprandial exercise required rapid modulation of insulin delivery. To demonstrate the effect of postprandial exercise on preprogrammed open-loop insulin replacement, four diabetic subjects were studied during breakfast with and without exercise while receiving a fixed open-loop insulin infusion pattern (6.1 +/- 0.7 U over 140 +/- 8 min). The glycemic response to breakfast alone was entirely normalized. However, symptomatic hypoglycemia occurred in all subjects when exercise was initiated 30 min after breakfast. The diabetic responses to closed-loop insulin infusion provide important data in defining the appropriate preprogrammed open-loop insulin infusion pattern for postprandial exercise.

Synergistic interaction between exercise and insulin on peripheral glucose uptake

The interaction of exercise and insulin on glucose metabolism was examined in 10 healthy volunteers. Four study protocols were used: study 1: plasma insulin was raised by approximately 100 microunits/ml while plasma glucose was maintained at basal levels for 2 h (insulin clamp). Study 2: subjects performed 30 min of bicycle exercise at 40% of VO2 max. Study 3: an insulin clamp was performed as per study 1. Following 60 min of sustained hyperinsulinemia, however, subjects exercised for 30 min as per study 2. Study 4: subjects were studied as per study 3 except that catheters were inserted into the femoral artery and vein to quantitate leg glucose uptake. During the 60-90 min period of hyperinsulinemia (study 1), glucose uptake averaged 8.73 +/- 0.10 mg/kg per min. With exercise alone (study 2), the increment in peripheral glucose uptake was 1.43 +/- 0.30 mg/kg per min. When hyperinsulinemia and exercise were combined (study 3), glucose uptake averaged 15.06 +/- 0.98 mg/kg per min (P less than 0.01) and this was significantly (P less than 0.001) greater than the sum of glucose uptake when exercise and the insulin clamp were performed separately. The magnitude of rise in glucose uptake correlated closely with the increase in leg blood flow (r = 0.935, P less than 0.001), suggesting that the synergism is the result of increased blood flow and increased capillary surface area to exercising muscle. More than 85% of total body glucose metabolism during studies 1 and 3 was accounted for by skeletal muscle uptake. These results demonstrate that (a) insulin and exercise act synergistically to enhance glucose disposal in man, and (b) muscle is the primary tissue responsible for the increase in glucose metabolism following hyperinsulinemia and exercise.

Effects of mild hyperinsulinemia on the metabolic response to exercise

To assess the effects of mild hyperinsulinemia on the metabolic adaptations to exercise, five normal male subjects were studied during 2 cycles of 30 min rest followed by 60 min mild exercise. During one cycle, insulin was infused at a rate of 0.33 mU/kg/min. During both cycles, plasma glucose concentration was kept constant by a glucose-controlled glucose infusion system. Studies with and without insulin were performed in random order, with 30 min between studies. During the insulin infusion, plasma non-esterified fatty acids fell during rest and failed to rise with exercise, indicating a limited availability of this substrate to working muscle. Insulin infusion also inhibited the expected rise in glycerol and 3-hydroxybutyrate normally observed during exercise. Plasma lactate concentrations at the completion of exercise with insulin infusion were higher than after exercise without insulin infusion. Greater metabolic dependence on carbohydrate metabolism is suggested by an increased respiratory quotient during insulin infusion. Insulin infusion had no significant effect on the amount of glucose which needed to be infused for maintaining a constant plasma glucose during rest, but there was a large and significant difference in the need for infused glucose during exercise with and without insulin infusion. The results indicate that even mild hyperinsulinism interferes with normal metabolic responses to exercise, and suggest that fall in insulin concentration seen with exercise is an important regulatory process, not merely a secondary consequences of a declining plasma glucose level.

Glucoregulatory and metabolic response to exercise in obese noninsulin-dependent diabetes

The metabolic response to exercise in obese postabsorptive noninsulin-dependent diabetics was compared to that of obese nondiabetics. Exercise consisted of 45 min on a cycle ergometer at 60% maximum oxygen consumption. Six diabetic subjects were studied during oral hypoglycemic therapy and four on diet alone. The sulfonylurea therapy had no effect on the response. Glycemia was elevated at rest in both diabetic subgroups (192 +/- 24 mg/dl for diet alone, 226 +/- 36 mg/dl for sulfonylurea treatment) and a similar fall (35 and 37 mg/dl, respectively) occurred with exercise. In control subjects, glycemia was 86 +/- 4 mg/dl and did not change with exercise. In the diabetics at rest, glucose production was elevated (220 +/- 25 mg/min), whereas the metabolic clearance of glucose was suppressed. During exercise the increase in glucose utilization was similar to that in controls, but glucose production failed to increase significantly, thus accounting for the decline in plasma glucose. At rest, plasma immunoreactive insulin (IRI) was elevated to 0.90 ng/ml in the controls and decreased to 0.65 ng/ml with exercise. In the diabetics IRI was similarly elevated (0.89 ng/ml) but failed to decrease normally with exercise. Lactate, pyruvate, alanine, and free fatty acids increased similarly in diabetics and controls, whereas the increase in 3-hydroxybutyrate during recovery was less in diabetics. The sustained insulinemia, the basal overproduction of glucose, and hyperglycemia itself may all contribute to the observed differences in glucose flux during exercise in noninsulin-dependent diabetics.

Diabetes and exercise

This review describes (1) the metabolic and hormonal response to exercise in normal and diabetic man, and (2) the potential benefits of physical training in diabetes. Whereas in normal man plasma glucose varies little during exercise, the insulin-dependent diabetic subject may experience an increase in plasma glucose, a modest decrease or a marked decrease which can result in symptomatic hypoglycemia. Evidence is reviewed that the glycemic response depends on the ambient plasma concentration of insulin and that this may be influenced by an effect of exercise on the absorbtion of insulin from its site of injection. The response to exercise of noninsulin-dependent diabetic subjects and of diabetic subjects with autonomic neuropathy is also described. Physical training improves glucose tolerance in some noninsulin-dependent diabetic subjects and in insulin-dependent patients, it may diminish insulin requirements. It may also have a role in retarding the development of cardiovascular complications. Physical training is not totally innocuous, however, and in many patients with diabetes special precautions are required.

Free fatty acid and ketone body metabolism during exercise in diabetes

In diabetic patients the metabolic response to physical exercise is to a large extent determined by the degree of insulin deficiency at the onset of exercise. Thus, in well-controlled insulin-treated patients with mild hyperglycaemia and no or minimal ketonemia the utilization of FFA, blood glucose and glycogen by working muscle is similar to that of healthy subjects, and exercise is accompanied by a fall in blood glucose levels. In contrast, patients in poor metabolic control with marked hyperglycaemia, elevated FFA levels and hyperketonemia may respond to exercise with a further rise in FFA, ketone levels and blood glucose, reflecting augmented rates of adipose tissue lipolysis and hepatic ketogenesis. The accelerated rate of ketogenesis seen during exercise continues unabated in diabetics but not in healthy subjects during the post-exercise recovery period, thereby contributing to the development of post-exercise ketosis. These considerations underscore the importance of adequate insulin administration in connection with exercise in diabetic patients.

Metabolic effects of physical training

Effects of physical training on factors associated with diabetes mellitus and its increased risk for cardiovascular disease are reviewed. Plasma insulin levels are decreased by training particularly in obesity and glucose tolerance seems to be improved. Training leads also in general to diminished body fat, but this is not obligatory for the plasma insulin decrease. There are no changes in concentrations of amino acids growth hormone or catecholamines, which can explain the insulin decrease. Cortisol is decreased the days after an acute exercise as well as after training in parallel with the plasma insulin decrease. The cortisol decrease may lead to changes in insulin receptor density in tissues leading to increased insulin sensitivity. The insulin decrease seems to be due to both a decreased production (to about 2/3) and an increased clearance (to about 1/3). Physical training leads to a decrease in plasma triglycerides and to a decrease in blood pressure. All these effects of physical training seem to be beneficial in the treatment of diabetes mellitus.

Energy Metabolism in Diabetic Distance Runners

The authors discuss chronic effects of serious endurance training on the management of diabetes and recommend ways of adjusting insulin administration to accommodate training schedules.

Sauna-induced acceleration in insulin absorption from subcutaneous injection site

The effect of the Finnish sauna on insulin absorption from a subcutaneous injection site was examined in eight insulin-dependent diabetic patients by measuring externally the disappearance rate of 125I-labelled rapid-acting insulin. The sauna (twice for 25 minutes at 85 degrees C) accelerated insulin absorption by 110% as compared with room temperature (p < 0.01). After the sauna blood glucose concentrations were 3.0-3.3 mmol/1 (54.1-59.5 mg/100 ml) lower than on the control day (p < 0.05). The fall in blood glucose values was proportional to the increased rate of insulin absorption (r = 0.30; p < 0.01). The hypoglycaemic effect of a sauna in insulin-treated diabetics is clearly at least partly due to enhanced insulin absorption from the injection site. Such an effect might be prevented by taking a snack or reducing the insulin dose.

Exercise in diabetes: therapeutic implications

The metabolic response to acute exercise in diabetics is largely determined by the availability of insulin. In nonketotic, insulin-dependent diabetics, acute exercise lowers the level of plasma glucose, whereas in insulin-deficient, ketotic patients, blood glucose may increase during exercise. Exercise accelerates insulin absorption from the exercising limb. Thus, by injecting insulin into a nonexercising area (eg, into the abdomen before leg exercise), the degree of exercise-induced hypoglycemia can be reduced in diabetic patients. Also, elevation in the level of antiinsulin hormones caused by exercise is exaggerated in diabetics if insulin treatment is less than optimal. This abnormal hormonal response may be restored to normal by improved methods of insulin delivery. In normal subjects, regular exercise or training results in enhanced body sensitivity to insulin. This rise in sensitivity may be mediated by augmented insulin binding to receptors. Furthermore, regular exercise may decrease levels of serum triglycerides and low-density lipoprotein cholesterol and increase those of high-density lipoprotein cholesterol. These beneficial effects of training on carbohydrate and lipid metabolism observed in normal subjects may extend to diabetic patients as well.

Effect of physical training on glucose tolerance and on glucose metabolism of skeletal muscle in anaesthetized normal rats

The effect of physical training on glucose tolerance in vivo and skeletal muscle glucose metabolism in vitro was investigated in normal rats. Treadmill running for 10 days up to 240 min/day led to a decrease of basal and glucose-stimulated plasma insulin levels without major alterations of the IV glucose tolerance (1 g/kg body weight). Swim training of two weeks' duration, i.e. exercise up to 2 X 75 min/day, which did not induce significant changes in body composition, skeletal muscle glycogen levels or citrate synthase activity, resulted in a significant improvement of IV glucose tolerance and substantial reductions of basal and glucose-stimulated plasma insulin levels. Associated with this apparent improvement of insulin sensitivity in vivo, significant increases of the insulin-stimulated glucose uptake (+ 55%) and lactate oxidation + 78%) in vitro were found on perfusion of the isolated hindquarter of swim-trained animals. It is suggested that mild physical training can improve glucose tolerance and insulin sensitivity in normal rats, at least in part, due to an increase of insulin sensitivity of skeletal muscle glucose metabolism.

Metabolic and hormonal changes during exercise in healthy, diabetic and obese subjects

The metabolic and hormonal changes during a standard physical exercise were studied in healthy subjects and in insulin-dependent diabetics well matched for body weight, and therefore submitted to a similar work load in a physiologic range, and in obese subjects that, owing to their weight, faced a significant heavier work in the same environmental conditions. Moderate work load did not lead to significant changes in metabolic and hormonal blood parameters (blood glucose, FFA and glycerol; insulin, glucagon, growth hormone and cortisol) in healthy subjects. A similar substrate homeostatis was seen in insulin-dependent diabetics, that however showed marked hormonal alterations. In these subjects, indeed, higher levels of plasma glucagon and GH were reached during work and in the recovery phase. Obese subjects, submitted to a heavier work load, presented a marked increase in blood glucose and glycerol which agrees with high GH and cortisol levels, and a subsequent increment of IRI which corresponds to a normalization of blood glucose and glycerol. Obese subjects, therefore, show a normal sensitivity to work load. Considerations about the work load in everyday life are discussed.

Blood amine acid levels in patients with insulin excess (functioning insulinoma) and insulin deficiency (diabetic ketosis)

Blood amino acid concentrations were determined in the postabsorptive state in nine patients with insulin excess (functioning insulinomas), nine juvenile-type diabetics with insulin deficiency (diabetic ketosis due to insulin withdrawal), six juvenile diabetics in moderate metabolic control, and five healthy control subjects. Blood branched-chain amino acid (BCAA) levels were elevated in diabetic ketosis and decreased in patients with insulinomas. Blood concentrations of BCAA were significantly correlated to blood glucose levels, and in diabetics they were also correlated to blood ketone bodies, serum free fatty acids, and glycerol levels. These data indicate an inverse relationship between circulating effective insulin levels and blood BCAA concentrations. It is suggested that blood levels of BCAA might represent an indicator of insulin-dependent alterations of protein metabolism.