Juha A. Tuominen

The effect of exercise on leptin concentration in healthy men and in type 1 diabetic patients.

PURPOSE Leptin is a recently discovered hormone that appears as a regulator of energy balance. It is important to know whether leptin concentrations are changed under conditions of altered energy homeostasis. Consequently, we examined the effects of exercise with fasting and exercise with feeding on circulating leptin concentrations in healthy men and in type 1 diabetic patients with normal body weight and well controlled diabetes. METHODS Leptin concentrations were determined with radioimmunoassay. RESULTS During a 3-h cycle ergometer exercise with fasting, leptin decreased by 42% (P < 0.01) in nine healthy men and by 23% (P = 0.05) in eight male type 1 diabetic patients. Leptin fell equally by 12% (P < 0.03) both in nine healthy men and in eight male type 1 diabetic patients who were studied as a resting control group. The absolute fall in leptin in healthy men was similar in the exercise and resting control groups (0.8 +/- 0.1 microgram.L-1 vs 0.8 +/- 0.2 microgram.L-1). However, due to lower leptin concentration before the exercise, the relative decrease (42%) was greater than during the resting control study (12%, P < 0.005). This difference was not seen in the diabetic patients. Fasting leptin concentration correlated positively with BMI (r = 0.75, P < 0.001) and fasting insulin (r = 0.71, P < 0.01) in healthy men as well as with insulin level (r = 0.54, p < 0.05) in type 1 diabetic patients. When exercise was performed with feeding, and this was associated with a significant rise in serum cortisol level (marathon run, 14 healthy men and 7 type 1 diabetic patients), leptin concentration did not change significantly. CONCLUSIONS 1) During morning hours, leptin decreases both in healthy men and in type 1 diabetic patients, reflecting a diurnal variation of leptin concentration and the effect of fasting on leptin concentration. 2) The fall in leptin during morning hours is augmented by physical exercise in healthy men. 3) If exercise is performed with feeding and associated with a rise in serum cortisol level, leptin concentration remains unchanged. These data suggest that although exercise may reduce circulating leptin levels, the effect is small and can be counterbalanced by feeding or a rise in serum cortisol concentration.

Intramuscular triglyceride content is increased in IDDM

Summary Increased lipid oxidation is related to insulin resistance. Some of the enhanced lipid utilization may be derived from intramuscular sources. We studied muscle triglyceride (mTG) concentration and its relationship to insulin sensitivity in 10 healthy men (age 29 ± 2 years, BMI 23.3 ± 0.6 kg/m2) and 17 men with insulin-dependent diabetes mellitus (IDDM) (age 30 ± 2 years, BMI 22.8 ± 0.5 kg/m2, diabetes duration 14 ± 2 years, HbA1 c 7.7 ± 0.3 %, insulin dose 48 ± 3 U/day). Insulin sensitivity was measured with a 4 h euglycaemic (5 mmol/l) hyperinsulinaemic (1.5 mU or 9 pmol · kg–1· min–1) clamp accompanied by indirect calorimetry before and at the end of the insulin infusion. A percutaneous biopsy was performed from m. vastus lateralis for the determination of mTG. At baseline the IDDM patients had higher glucose (10.2 ± 0.9 vs 5.6 ± 0.1 mmol/l, p < 0.001), insulin (40.3 ± 3.2 vs 23.2 ± 4.2 pmol/l, p < 0.01), HDL cholesterol (1.28 ± 0.06 vs 1.04 ± 0.03 mmol/l, p < 0.01) and mTG (32.9 ± 4.6 vs 13.6 ± 2.7 mmol/kg dry weight, p < 0.01) concentrations than the healthy men, respectively. The IDDM patients had lower insulin stimulated whole body total (–25 %, p < 0.001), oxidative (–18 %, p < 0.01) and non-oxidative glucose disposal rates (–43 %, p < 0.001), whereas lipid oxidation rate was higher in the basal state ( + 44 %, p < 0.01) and during hyperinsulinaemia ( + 283 %, p < 0.05). mTG concentrations did not change significantly during the clamp or correlate with insulin stimulated glucose disposal. In healthy men mTG correlated positively with lipid oxidation rate at the end of hyperinsulinaemia (r = 0.75, p < 0.05). In conclusion: 1) IDDM is associated with increased intramuscular TG content. 2) mTG content does not correlate with insulin sensitivity in healthy subjects or patients with IDDM. [Diabetologia (1998) 41: 111–115]

Athletes with IDDM exhibit impaired metabolic control and increased lipid utilization with no increase in insulin sensitivity.

Physical exercise is traditionally recommended to diabetic patients as part of their treatment. Although healthy athletes exhibit enhanced skeletal muscle insulin sensitivity, the metabolic effects of vigorous training in patients with insulin-dependent diabetes mellitus (IDDM) are not known. This study was designed to examine the effects of competitive sports on fuel homeostasis and insulin sensitivity in athletes with IDDM. We studied 11 athletes and 12 matched sedentary men with IDDM. In each subject, we measured glycemic control, insulin-stimulated glucose uptake in the whole body and forearm, rates of glucose and lipid oxidation, and muscle glycogen, glycogen synthase, and glucose transport protein (GLUT4) concentrations. The athletes had higher VO2max (52 ± 1 vs. 42 ± 1 ml.kg−1 · min−1, P < 0.001) and HbA1c levels (8.4 ± 0.4 vs. 7.2 ± 0.2%, P < 0.05) than sedentary patients, but took smaller insulin doses (41 ± 3 vs. 53 ± 3 U/day, P < 0.05). The insulin-stimulated rates of whole-body and forearm glucose uptake and glucose oxidation were similar in the two groups, whereas both energy expenditure and lipid oxidation were increased in the athletes. Lipid oxidation correlated inversely with glycogen synthase activity. The mean glucose arterialized venous blood-deep venous blood (A-V) difference during the insulin infusion (60-240 min) correlated with the whole-body glucose disposal throughout the insulin infusion (after 60 min, r > 0.73, P < 0.001 for all 30-min periods). This association is accounted for by the relationship between glucose A-V difference and nonoxidative glucose disposal. Muscle glycogen and GLUT4 protein contents were not different in the two groups. In conclusion, in athletes with IDDM: 1) competitive exercise performed at variable schedules and intensities leads to a decrease in required insulin dose, impairment of metabolic control, and increase in lipid utilization; 2) insulin sensitivity is not enhanced; and 3) glucose A-V difference, not blood flow, is the major determinant of body sensitivity to insulin. Thus, more intense glucose monitoring and education may be required for the maintenance of good control in patients with IDDM involved in competitive sports.

Long-Term Lisinopril Therapy Reduces Exercise-Induced Albuminuria in Normoalbuminuric Normotensive IDDM Patients

OBJECTIVE To study the effect of lisinopril on the exercise-induced urinary albumin excretion rate. RESEARCH DESIGN AND METHODS A total of 26 IDDM patients with normoalbuminuria were randomized into two groups, with one group receiving placebo (n = 13, age 36 ± 3 years, BMI 24.5 ± 1.1 kg/m2) and the other group receiving an average of 15 mg lisinopril daily (n = 13, age 34 ± 2 years, BMI 24.4 ± 0.9 kg/m2). Overnight and exercise-induced urinary albumin excretion rate was measured at baseline and after 1 and 2 years of treatment. Two patients in the placebo group and none in the lisinopril group developed microalbuminuria. RESULTS In the lisinopril group, the exercise-induced urinary albumin excretion rate diminished 46% after the 1st year (P = 0.059) and 66% (P < 0.01) after the 2nd year. However, it remained unchanged in the control group. Systolic blood pressure (sBP) and diastolic blood pressure (dBP) were similar at baseline and after 1 year, but at 2 years, sBP was 13 mmHg lower (P = 0.03) and dBP was 9 mmHg lower (P = 0.052) in the lisinopril group as compared with the control group. The dBP decreased significantly at 1 and 2 years in the lisinopril group, while there was no significant change in the sBP. In the whole group at baseline, the overnight albumin excretion rate correlated with HbA1c (r = 0.50, P < 0.01) and the duration of diabetes (r = 0.39, P < 0.05), and sBP correlated with both the overnight (r = 0.42, P < 0.05) and the exercise-induced (r = 0.48, P < 0.05) albumin excretion rate. CONCLUSIONS Glycemic control and blood pressure are directly related to the overnight albumin excretion rate also in normotensive normoalbuminuric IDDM patients. Lisinopril treatment reduces the exercise-induced urinary albumin excretion rate in such patients. These data suggest a protective effect of lisinopril against the development of microalbuminuria.

Seven years of remission in a type I diabetic patient : influence of cyclosporin and regular exercise

Objective— To analyze factors contributing to a long-term remission in a patient with type I diabetes. Research Design and Methods— The patient was treated with cyclosporin for 16 mo after a short duration of symptoms. During the 7-yr follow-up, we tracked his glycemic control, oral glucose tolerance, insulin sensitivity, endogenous insulin secretion, and β-cell immunology. The results are compared with those of matched diabetic patients and healthy control subjects. Results— Insulin therapy was discontinued after 5 wk. Thereafter the patient had normal fasting and home blood glucose concentrations and near-normal HbA1c without insulin therapy for 7 yr. During this period, he maintained islet cell antibodies, although his basal and glucagon-stimulated C-peptide concentrations were normal. He participated in active physical training and had an insulin sensitivity higher than in sedentary control subjects or trained diabetic patients and equal to that in healthy athletes. His oral glucose tolerance decreased gradually and became diabetic during the last 3 yr. Conclusions— In this patient, an early start of cyclosporin therapy probably contributed to the maintenance of endogenous insulin secretion, and insulin sensitivity was high because of physical training. Consequently, the patient was able to maintain normoglycemia without exogenous insulin therapy for 7 yr.

The Association of Acetyl-L-Carnitine With Glucose and Lipid Metabolism in Human Muscle In Vivo: The Effect of Hyperinsulinemia

We examined whether hyperinsulinemia is associated with changes in the amount of L-carnitine and acetyl-L-carnitine in the muscle and whether the source of acetyl-coenzyme A (CoA) (glucose or free fatty acids [FFAs]) influences its further metabolism to acetyl-L-carnitine or through tricarboxylic acid in the skeletal muscle of man in vivo. Twelve healthy men (aged 45 +/- 2 years; body mass index, 25.2 +/- 1.0 kg/m2) were studied using a 4-hour euglycemic-hyperinsulinemic clamp (1.5 mU/kg/min) and indirect calorimetry. Although the mean muscle free L-carnitine and acetyl-L-carnitine concentrations remained unchanged during hyperinsulinemia in the group as a whole, the individual changes in muscle free L-carnitine and acetyl-L-carnitine concentrations were inversely related (r = -.72, P < .02). The basal level of acetyl-L-carnitine was inversely related to the rate of lipid oxidation (r = -.70, P < .02). In a stepwise linear regression analysis, 77% of the variation in the change of acetyl-L-carnitine concentrations was explained by the basal muscle glycogen level (inversely) and nonoxidative glucose disposal rate (directly) during hyperinsulinemia (P < .001); by adding the final FFA concentration (inverse correlation) to the model, 88% of the variation was explained (P < .001). In conclusion, (1) hyperinsulinemia does not enhance skeletal muscle free L-carnitine or acetyl-L-carnitine concentrations in-man, and (2) the acetyl group of acetyl-L-carnitine in human skeletal muscle in vivo is probably mostly derived from glucose and not through beta-oxidation from fatty acids.

Blood flow, lipid oxidation, and muscle glycogen synthesis after glycogen depletion by strenuous exercise.

UNLABELLED We studied the interrelationship between blood flow, glycogen synthesis, and glucose and lipid utilization in 14 healthy men. A 4-h euglycemic insulin clamp with indirect calorimetry and muscle biopsies were done after a glycogen depletion (exercise) and after a resting day (control). In spite of the exercise induced decrease in leg muscle glycogen content (28% in the basal state, 22% after hyperinsulinemia, P < 0.05 in both as compared with the control study), basal or insulin stimulated glycogen synthase activity remained unchanged. In the basal state, glucose oxidation was 54% lower (P < 0.001) and lipid oxidation 108% higher (P < 0.001) after the glycogen depletion as compared with that in the control study. During the post-depletion insulin clamp, the glucose oxidation rate was 17% lower (P < 0.02) and lipid oxidation 169% higher (P < 0.01), while the whole body total glucose disposal was similar in both studies. Baseline forearm blood flow was similar and increased equally by over 40% during both insulin clamp studies (P < 0.05). Basal glucose extraction after glycogen depletion study was one third of that in the control study (P < 0.05). Both basal and insulin stimulated leg muscle glycogen content correlated inversely with basal forearm blood flow (r = -0.69, P < 0.01 and r = -0.82, P < 0.001, respectively) and basal lipid oxidation (r = -0.54, P < 0.05 and r = -0.64, P < 0.01, respectively) after glycogen depletion. Basal glycogen synthase fractional activity correlated positively with forearm blood flow (r = 0.78, P < 0.001) and forearm glucose uptake (r = 0.71, P < 0.05) during the insulin infusion. IN CONCLUSION 1) the unchanged insulin sensitivity in the face of glycogen depletion is probably a result of increased lipid oxidation, and 2) blood flow is related inversely to muscle glycogen content and directly to glycogen synthase activity.