The effects of diabetes mellitus, exercise, and single doses of biguanides upon lactate metabolism in man

Metformin does not compromise energy status in human skeletal muscle at rest or during acute exercise: A randomised, crossover trial

5´AMP-activated protein kinase (AMPK) is a mediator of a healthy metabolic phenotype in skeletal muscle. Metformin may exacerbate the energy disturbances observed during exercise leading to enhanced AMPK activation, and these disturbances may provoke early muscular fatigue. We studied acute (1 day) and short-term (4 days) effects of metformin treatment on AMPK and its downstream signaling network, in healthy human skeletal muscle and adipose tissue at rest and during exercise, by applying a randomized blinded crossover study design in 10 lean men. Muscle and fat biopsies were obtained before and after the treatment period at rest and after a single bout of exercise. Metformin treat ment elicited peak plasma and muscle metformin concentrations of 31 μM and 11 μM, respectively. Neither of the treatments affected AMPK activity in skeletal muscle and adipose at rest or during exercise. In contrast, whole-body stress during exercise was elevated as indicated by increased plasma lactate and adrenaline concentrations as well as increased heart rate and rate of perceived exertion. Also whole-body insulin sensitivity was enhanced by 4 days metformin treatment, that is reduced fasting plasma insulin and HOMA-IR. In conclusion, acute and short-term metformin treatment does not affect energy homeostasis and AMPK activation at rest or during exercise in skeletal muscle and adipose tissue of healthy subjects. However, metformin treatment is accompanied by slightly enhanced perceived exertion and whole-body stress which may provoke a lesser desire for physical activity in the metformin-treated patients.

Cardiovascular, metabolic and hormonal responses to the progressive exercise performed to exhaustion in patients with type 2 diabetes treated with metformin or glyburide

OBJECTIVES

To evaluate the effects of Metformin and Glyburide on cardiovascular, metabolic and hormonal parameters during progressive exercise performed to exhaustion in the post-prandial state in women with type 2 diabetes (T2DM).

DESIGN AND METHODS

Ten T2DM patients treated with Metformin (M group), 10 with Glyburide (G group) and 10 age-paired healthy subjects exercised on a bicycle ergometer up to exercise peak. Cardiovascular and blood metabolic and hormonal parameters were measured at times -60 min, 0 min, exercise end, and at 10 and 20 minutes of recovery phase. Thirty minutes before the exercise, a standard breakfast was provided to all participants. The diabetic patients took Metformin or Glyburide before or with meal.

RESULTS

Peak oxygen uptake (VO(2)) was lower in patients with diabetes. Plasma glucose levels remained unchanged, but were higher in both diabetic groups. Patients with diabetes also presented lower insulin levels after meals and higher glucagon levels at exercise peak than C group. Serum cortisol levels were higher in G than M group at exercise end and recovery phase. Lactate levels were higher in M than G group at fasting and in C group at exercise peak. Nor epinephrine, GH and FFA responses were similar in all 3 groups.

CONCLUSION

Progressive exercise performed to exhaustion, in the post-prandial state did not worsen glucose control during and after exercise. The administration of the usual dose of Glyburide or Metformin to T2DM patients did not influence the cardiovascular, metabolic and hormonal response to exercise.

The effects of metformin and glibenclamide on glucose metabolism, counter-regulatory hormones and cardiovascular responses in women with Type 2 diabetes during exercise of moderate intensity

AIMS

To compare the effects of metformin and glibenclamide on cardiovascular, metabolic and hormonal parameters during exercise of moderate intensity performed in the postprandial state, in women with Type 2 diabetes.

METHODS

Ten patients treated with metformin, 10 with glibenclamide and 10 control subjects (C) exercised on a bicycle ergometer at 50% of oxygen uptake (VO(2)) peak for 45 min. Cardiovascular, blood metabolic and hormonal parameters were determined at times -60 min (fasting), 0, +15, +30, +45 min (exercise) and at +60, +90 min (recovery). Thirty minutes prior to exercise, participants consumed a standard breakfast. Patients with diabetes took metformin or glibenclamide before the meal.

RESULTS

Systolic and diastolic blood pressure and plasma glucose were higher in both diabetic groups, for the whole experiment. Blood glucose did not change during exercise in the three groups and increased at recovery only in the control group. Plasma glucagon concentrations at the end of exercise and recovery, and plasma lactate concentrations at recovery were higher in the metformin group. Insulin, noradrenaline, growth hormone, cortisol and free fatty acid responses were similar in all three groups.

CONCLUSIONS

Our results suggest that the usual dose of glibenclamide and metformin can be taken safely before postprandial exercise of moderate intensity without affecting cardiovascular, metabolic and hormonal responses. However, after exercise, glibenclamide and metformin prevent the normal rise in blood glucose and metformin delays the fall in plasma lactate concentrations.

Protection by lactate of cerebral function during hypoglycaemia

Severe hypoglycaemia with brain dysfunction limits intensified therapy in patients with insulin-dependent diabetes mellitus, despite evidence that such therapy reduces the risk of chronic complications of the disease. We have investigated the effect of infusing lactate (a potential non-glucose fuel for brain metabolism) on protective, symptomatic neurohumoral responses and on brain function during hypoglycaemia in seven healthy men. Elevation of lactate (within a physiological range) substantially diminished catecholamines, growth hormone, cortisol, and symptomatic responses to hypoglycaemia and lowered the glucose level at which these responses began. Glucagon responses were unaffected. Lactate was also associated with a significant lowering of the glucose level at which brain function deteriorated, suggesting that brain function was protected during the hypoglycaemia. The defect in counter-regulation is similar to that seen in hypoglycaemia-prone diabetic patients. Initiation of the protective responses to hypoglycaemia (except glucagon) can be delayed by supporting metabolism with an alternative metabolic fuel. Cerebral cortical dysfunction of severe hypoglycaemia is also delayed. Our demonstration that higher brain function can be protected during hypoglycaemia may have therapeutic potential.

Genetic polymorphism of sparteine/debrisoquine oxidation: a reappraisal

Polymorphic oxidation of the sparteine/debrisoquine-type has been shown to account for much of the interindividual variation in the metabolism, pharmacokinetics and pharmacodynamics of an increasing number of drugs, including some antiarrhythmic, antidepressant and beta-adrenoceptor antagonist agents. Impaired hydroxylation of these drugs results from the absence of the enzyme cytochrome P450IID6 in the livers of poor metabolisers, who constitute 6% to 10% of Caucasian populations. The clinical importance of the phenomenon has to be explored further and for most sparteine/debrisoquine-related substrates there is a need for controlled prospective studies to define the consequences to the patient of impaired or enhanced drug oxidation.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Clinical pharmacokinetics and endocrine disorders. Therapeutic implications

Endocrine disorders are common and produce widespread changes in cellular and organ function. Alterations in the sensitivity of patients with thyroid disorders to digoxin, anticoagulants and sedatives have been recognised for many years. Many of the recently documented kinetic alterations in endocrine patients are explicable on the basis of disease-induced changes in hepatic drug metabolism, protein binding and renal function. In hyperthyroidism the rate of absorption of paracetamol, propranolol and oxazepam is increased due to increased gastrointestinal motility. The volume of distribution of propranolol and digoxin is increased and there is decreased binding of both basic and acidic drugs as a consequence of alterations in alpha 1-acid glycoprotein and albumin concentration. The rate of glucuronidation of paracetamol and oxazepam is increased in hyperthyroidism. While oxidative metabolism of antipyrine, propranolol, metoprolol and theophylline is enhanced, the clearance of a number of other agents, including diazepam, warfarin, antithyroid drugs and phenytoin, is unaltered. The systemic clearance of propranolol is enhanced as a consequence of a 50% increase in liver blood flow. The rate of elimination of a number of endogenous substances, including cortisol, thyroid hormones and insulin, also appear to be enhanced. Hyperthyroidism has a variable effect on renal function, with a possible increase in digoxin elimination, but no effect on the clearance of renally excreted beta-blockers, atenolol, sotalol and nadolol. These kinetic changes suggest that individualization and higher than normal dosage of propranolol is necessary to control hyperthyroidism, and in thyrotoxic atrial fibrillation higher doses of digoxin or additional therapy with beta-blockers, or verapamil, may be indicated. The increased sensitivity of thyrotoxic patients to warfarin suggest care with dosage and frequent monitoring of response are warranted. Less information is available concerning hypothyroidism, but there is a general trend for decreased absorption of paracetamol and propranolol. In addition, the volume of distribution of digoxin is reduced, as is renal clearance. Limited studies suggest no alteration in the glucuronidation of oxazepam, but antipyrine clearance appears to be reduced. Steady-state propranolol concentrations are elevated in hypothyroidism and there appears to be a decreased metabolism of thyroid hormones and cortisol. Preliminary information suggests the binding of propranolol is increased. Thus, in the treatment of hypothyroid patients, a lower dosage of propranolol may be required.(ABSTRACT TRUNCATED AT 400 WORDS)