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

Effects of the dimethyl ester on succinic acid on the hormonal and metabolic response to exercise in hereditarily diabetic starved rats

This study was designed to assess the effect of the dimethyl ester of succinic acid (SAD) upon the hormonal and metabolic response to a 60-min exercise in overnight-starved Goto-Kakizaki rats. Twenty Goto-Kakizaki rats were starved overnight and then either maintained at rest or obliged to swim for 60 min. Half of the rats were injected intraperitoneally with the dimethyl ester of succinic acid (SAD, 5.0 micromol g(-1) body wt) immediately before exercise (or 60 min of rest). In the hereditarily diabetic rats, overnight starvation lowered the plasma D- glucose, insulin and lactate concentrations, while increasing that of free fatty acids and beta-hydroxybutyrate. In resting rats, the injection of SAD increased the glycogen content of liver, heart and muscle and the plasma concentration of D-glucose, insulin, glycerol and free fatty acids. In control animals, not injected with SAD, exercise increased the plasma concentration of D- glucose, lactate and glycerol, whilst lowering both that of insulin and the glycogen content of liver, heart and muscle. The injection of SAD before exercise failed to prevent and, on occasion, even accentuated the changes in both the glycogen content of liver, heart and muscle and the plasma concentration of D-glucose, insulin, glycerol and free fatty acids, whilst minimizing the increase in lactate concentration otherwise caused by exercise. Nevertheless, the comparison between resting and exercising rats, both injected with SAD, suggested that the ester abolished the exercise-induced rise in D-glucose, glycerol and fatty acid concentrations. By comparison with comparable experiments conducted in overnight-starved normal rats, these findings emphasize both the difference between normal and diabetic rats in their metabolic response to exercise, especially in terms of changes in glycemia, and the usefulness of SAD to compensate for the increased consumption of endogenous nutrients during exercise.

Exercise prescription for individuals with metabolic disorders. Practical considerations

Regular exercise has been recognised as an important component in the management of patients with diabetes mellitus. In addition to acutely lowering blood glucose, exercise training improves glucose tolerance and peripheral insulin sensitivity, contributes to weight loss and reduces several risk factors for cardiovascular disease. When proper precautions are taken to prevent hypoglycaemia, individuals with diabetes can enjoy the same benefits from exercise as nondiabetic healthy individuals. As a guideline, moderate intensity, aerobic endurance activities should be performed for 20 to 40 minutes at least 3 times a week. Blood glucose should be monitored, and insulin dose and carbohydrate intake adjusted based on the blood glucose response to the type and duration of exercise. This review will summarise current understanding of the therapeutic role of exercise in the treatment of diabetes and will present guidelines for prescribing exercise in diabetic patients.

Exercise for patients with diabetes. Benefits, risks, precautions

Exercise is beneficial in both prevention and control of non-insulin-dependent (type II) diabetes. Whether a patient has insulin-dependent or type II diabetes, a regular exercise program can produce positive changes in the lipid profile, reduce blood pressure and weight, and improve other cardiovascular risk factors. The risks of an exercise program include precipitation of cardiovascular events, damage to the soft tissue and joints of the feet, visual loss, early and delayed hypoglycemia, and hyperglycemia and ketosis. Consequently, a comprehensive clinical assessment to identify potentially harmful diabetic complications and to determine the patient's fitness level is needed before a suitable exercise program can be prescribed. With careful manipulation of insulin doses and home monitoring of blood glucose levels, exercise need not adversely affect glycemic control. Moreover, the metabolic and cardiovascular benefits that result from a sensible exercise program can greatly improve the quality of life for most diabetic patients.

Ketone body production and disposal: effects of fasting, diabetes, and exercise

Turnover studies performed during progressive fasting in normal subjects indicate that the production rate and the concentration of KB rise markedly during the early phase of fasting and start reaching a plateau after about 5 days. In addition to increased production, a reduction in the metabolic clearance rate of KB contributes to the hyperketonemia. This reduced metabolic clearance rate reflects essentially the progressive saturation of muscular ketone uptake that occurs with increasing ketonemia. The hormonal and metabolic environment of fasting plays only a minor role in this process, since a fall in KB metabolic clearance similar to that observed during fasting is observed if hyperketonemia is artificially induced in the postabsorptive state by the infusion of exogenous ketones. As extraction of KB by muscle becomes limited during ongoing fasting, KB are preferentially taken up by the brain to serve as a substrate replacing glucose. The remarkable stability of ketonemia during prolonged fasting is maintained through the operation of a negative feedback mechanism whereby KB tend to restrain their own production rate. The antilipolytic and insulinotropic effects of KB are instrumental in this process. This homeostatic mechanism maintains ketogenesis only slightly above the maximal metabolic disposal rate, the difference corresponding to urinary excretion, which is always below 10% of total turnover under physiologic conditions. When type I insulin-deprived diabetic patients are compared at the same KB concentration with control subjects with fasting ketosis, the characteristics of KB kinetics are comparable in the two groups. The maximal KB removal capacity is identical in the two situations, and it is not possible to identify a ketone removal defect specific to diabetes. Thus, these data favor the concept that excessive production of KB represent the main factor leading to uncontrolled hyperketonemia. It should be realized that a production exceeding only slightly that prevailing during prolonged fasting is sufficient to cause a progressive build-up in concentration, leading to uncontrolled diabetic ketosis. In the overnight-fasted state, a prolonged exercise (2 h) performed at moderate intensity (50% VO2 max) stimulates the capacity of muscle to extract ketones from blood as evidenced by a stimulation of the metabolic clearance rate.(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.