Eva Hagström-Toft

Self-monitoring of blood glucose in type I diabetic patients: comparison with continuous microdialysis measurements of glucose in subcutaneous adipose tissue during ordinary life conditions.

OBJECTIVE To evaluate whether frequent self-monitoring of blood glucose (SMBG) sufficiently reflects the true diurnal glucose control during ordinary daily life in type I diabetic patients. RESEARCH DESIGN AND METHODS By using a microdialysis technique, continuous monitoring of adipose tissue glucose was performed in 24 type I diabetic patients during ambulatory conditions. A microdialysis probe was implanted subcutaneously and perfused by a portable microinfusion pump. Dialysate fractions were collected in 1- to 2-h samples during 3 consecutive days. The diurnal microdialysis glucose profiles were compared with those obtained by SMBG recordings performed seven times a day. RESULTS In seven patients, the SMBG profiles showed marked aberrations as compared to the continuous microdialysis glucose recordings; during the 3-day study period, 5–6 inconsistencies were registered. In only 4 patients (17%) did SMBG provide a valid reflection (0–2 inconsistencies) of the diurnal glucose profile, whereas in 13 patients the SMBG recordings paralleled the diurnal adipose tissue glucose profiles in an intermediate way (3–4 major inconsistencies). The inaccuracy of the SMBG data was due more often to the fact that wide glucose swings remained unrecognized, rather than to erroneous testing techniques (P < 0.05), and it was more evident during the night (P < 0.05). CONCLUSIONS In many type I diabetic patients, the true diurnal variability in glycemia is too great to be accurately reflected even by frequent self-monitoring of blood glucose.

Protracted glucose fall in subcutaneous adipose tissue and skeletal muscle compared with blood during insulin-induced hypoglycaemia

SummaryThe absolute glucose concentrations in subcutaneous adipose tissue and skeletal muscle were determined with microdialysis in 10 normal-weight, healthy subjects during a standardized hyperinsulinaemic hypoglycaemic clamp. The concentration of tissue dialysate glucose was measured in 15-min fractions and compared with that in arterialized venous plasma. Insulin (0.15 U · kg-1· h-1) was infused i. v. to lower the plasma glucose level to 2.5 mmol/1 over 30 min. This level was maintained for 30 min by using a variable glucose infusion. Thereafter, the insulin infusion was stopped and the plasma glucose level was gradually increased to baseline levels over 120 min. During a 60-min basal period, the glucose levels in muscle were 0.6 mmol/1 lower than those in plasma (p = 0.002), whereas the levels in adipose tissue and plasma were similar. The glucose nadirs in muscle (1.6 ± 0.1 mmol/1) and adipose tissue (2.0 ± 0.1 mmol/1) were significantly lower than that in plasma (2.4 ± 0.1 mmol/1) (p = 0.001 and 0.02, respectively), and the time-to-nadir was substantially longer in muscle (69 ± 5 min) and adipose tissue (57 ± 2 min) than in plasma (39 ± 3 min) (p = 0.0004). When the insulin infusion was stopped, the increases in adipose tissue and muscle glucose concentrations were delayed by approximately 25 and 45 min, respectively, as compared to the increase in plasma glucose. Thus, it seems that glucose measurements in adipose tissue and muscle more adequately reflect overall tissue homeostasis than do measurements in blood and that clinically relevant tissue glucopenia may be overlooked by conventional blood glucose measurements.

β-Adrenergic regulation of lipolysis and blood flow in human skeletal muscle in vivo

Little is known about the regulation of catecholamine-stimulated lipolysis in human skeletal muscle. Therefore, β-adrenergic regulation of lipolysis and blood flow was investigated in healthy subjects in vivo by use of microdialysis of the gastrocnemius muscle. First, during a hypoglycemic, hyperinsulinemic clamp, which induces a lipolytic response in skeletal muscle tissue, the muscle was locally perfused with β-adrenoceptor blocking agents. Perfusion with nonselective (propranolol) and β2-selective (ICI-118551) blocking agents counteracted the hypoglycemia-induced lipolysis ( P < 0.01), but perfusion with metoprolol (β1-blocker) did not affect the glycerol response. Second, selective β-adrenoceptor agonists were perfused in situ into skeletal muscle during resting conditions. β2-Adrenoceptor stimulation with terbutaline induced a concentration-dependent increase in skeletal muscle glycerol levels and in tissue blood flow, whereas perfusion with β1- or β3-adrenoceptor agonists (dobutamine or CGP-12177) did not influence the glycerol concentration or blood flow. In conclusion, in skeletal muscle tissue, only the β2-subtype is of importance among β-adrenoceptors for regulation of lipolysis and blood flow. This is in contrast to adipose tissue, where β1- and β3-adrenoceptors are also involved.

A circadian rhythm in lipid mobilization which is altered in IDDM

Summary It is not clear how circadian lipolysis and circulating concentrations of non-esterified fatty acids (NEFA) are altered in intensively treated insulin-dependent diabetic (IDDM) patients. Ten IDDM patients on an intensive insulin regimen and eight healthy control subjects were investigated under ordinary living conditions for 27 h by microdialysis of subcutaneous adipose tissue. The true tissue glycerol concentration and adipose blood flow changes were monitored as an index of lipolysis. A circadian pattern in adipose tissue lipolysis was observed in both groups, decreasing during the day and increasing during evening-night. The daytime decrease was normal, but the evening-night rise was elevated in IDDM (p = 0.03). Circulating NEFA decreased during the day and increased at night. The latter increase was enhanced threefold in IDDM (p = 0.003) and correlated with fasting glucose levels (r = 0.77). Nocturnal growth hormone (GH) was increased fivefold in IDDM and correlated to nocturnal lipolysis (r = 0.83). Adipose tissue blood flow increased during the night in a similar fashion in both groups. Near-normalization of glucose for 24 h in IDDM did not affect the nocturnal increases in NEFA, GH and lipolysis. In conclusion, a circadian rhythm in lipolysis was found. Increased lipolytic rates during evening-night may at least in part raise nocturnal circulating NEFA. Nocturnal NEFA and lipolysis are further enhanced in IDDM, maybe due to elevated GH, but not to insulinopenia or hyperglycaemia. [Diabetologia (1997) 40: 1070–1078]

Role of Phosphodiesterase III in the Antilipolytic Effect of Insulin in Vivo

The effect of three types of phosphodiesterase (PDE) inhibitors on in vivo antilipolysis was investigated in healthy subjects using a 2-h euglycemic, hyperinsulinemic (40 mU · m-2·min) clamp together with microdialysis of abdominal subcutaneous adipose tissue. During hyperinsulinemia (∼330 pmol/l), the circulating glycerol concentration was reduced to ∼50% of the basal level of 53.2 ± 3.6 μmol/l, indicating an antilipolytic effect. The decrease in adipose tissue dialysate glycerol, which mirrors the change in interstitial glycerol concentration, was about 40% during hyperinsulinemia when Ringers solution alone was perfused. Local perfusion with a selective PDE IV inhibitor, rolipram (10−4) mol/l), did not influence the insulin-induced decrease in dialysate glycerol (F = 0.8 vs. perfusion with Ringers solution by two-factor analysis of variance [ANOVA]), although rolipram increased the dialysate glycerol level by 144 ± 7% of the baseline value. However, local perfusion with a selective PDE III inhibitor, amrinone (10−3) mol/l), or a nonselective PDE inhibitor, theophylline (10−2) mol/l), abolished the ability of insulin to lower dialysate glycerol (F = 16.5, P < 0.01 and F = 8.5, P < 0.01, respectively, as compared with perfusion with Ringers solution). The findings could not be explained by changes in the local blood flow (as measured by a microdialysis–ethanol escape technique), which was not affected by hyperinsulinemia in the presence or the absence of PDE inhibitors in the dialysis solvent. We conclude that PDEs play an important role in mediating the antilipolytic effect of insulin in vivo and that PDE III is the dominant isoenzyme modulating this effect.

Effect of insulin on human adipose tissue metabolism in situ. Interactions with beta-adrenoceptors

SummaryThe effects of insulin, and its interactions with catecholamines through beta-adrenoceptors, on human adipose tissue glucose utilization and lipolysis were investigated in vivo. Microdialysis of the extracellular compartment of abdominal subcutaneous adipose tissue was performed in healthy subjects of normal weight, before and during a 2-h hyperinsulinaemic (61±3 mU/l), euglycaemic clamp. The tissue was perfused with or without the beta-adrenergic agonist isoproterenol (10−mol/l), and the tissue dialysate concentrations of glucose, glycerol (lipolysis index) lactate and pyruvate were determined. During the insulin infusion, glucose in adipose tissue decreased by 20% (p<0.001), despite arterial steady-state normoglycaemia. The concentrations of lactate and pyruvate increased gradually to a steadystate plateau of twice the basal level in adipose tissue and arterial blood. Insulin-induced suppression of glycerol (lipolysis index) was, if anything, more marked in adipose tissue than in plasma (65% vs 50% decrease from baseline levels, p<0.05). In situ perfusion of adipose tissue with isoproterenol, starting either at the beginning of the study period or at 45 min after initiation of the insulin infusion, resulted in marked and rapid elevations of all the investigated metabolites in the adipose tissue extracellular compartment (p<0.05–0.005).Itis concluded that insulin action on glucose uptake and lipolysis in human adipose tissue in vivo is counteracted by beta-adrenoceptor stimulation. In contrast, insulin and beta-adrenoceptors have synergistic effects on non-oxidative glucose metabolism in human adipose tissue in situ.

Major differences in noradrenaline action on lipolysis and blood flow rates in skeletal muscle and adipose tissue in vivo

Aims/hypothesisThe regulation of skeletal muscle lipolysis is not fully understood. In the present study, the effects of systemic and local noradrenaline administration on lipolysis and blood flow rates in skeletal muscle and adipose tissue were studied in vivo.MethodsFirst, circulating noradrenaline levels were raised tenfold by a continuous i.v. infusion (n=12). Glycerol levels (an index of lipolysis) were measured in m. gastrocnemius and in abdominal adipose tissue using microdialysis. Local blood flow was determined with the 133Xe clearance technique and whole-body lipolysis rates assessed with a stable glycerol isotope technique ([2H5] glycerol). Second, interstitial glycerol levels in m. gastrocnemius, m. vastus and adipose tissue were measured by microdialysis during local perfusion with noradrenaline (10−8–10−6 mol/l) (n=10). Local blood flow was monitored with the ethanol perfusion technique.ResultsWith regard to systemic noradrenergic stimulation, no change in fractional release of glycerol (difference between tissue and arterial glycerol) was seen in skeletal muscle. In adipose tissue it transiently increased twofold (p<0.0001), and the rate of appearance of glycerol in plasma showed the same kinetic pattern. Blood flow was reduced by 40% in skeletal muscle (p<0.005) and increased by 50% in adipose tissue (p<0.05). After noradrenaline stimulation in situ, a discrete elevation of skeletal muscle glycerol was registered only at the highest concentration of noradrenaline (10−6 mol/l) (p<0.05). Adipose tissue glycerol doubled already at the lowest concentration (10−8 mol/l) (p<0.05). In skeletal muscle a decrease in blood flow was seen at the highest noradrenaline concentrations (p<0.05).Conclusions/interpretationLipolysis and blood flow rates are regulated differently in adipose tissue and skeletal muscle. Adipose tissue displays a high, but transient (tachyphylaxia) sensitivity to noradrenaline, leading to stimulation of both lipolysis and blood flow rates. In skeletal muscle, physiological concentrations of noradrenaline decrease blood flow but have no stimulatory effect on lipolysis rates.

Effects of Insulin Deprivation and Replacement on In Vivo Subcutaneous Adipose Tissue Substrate Metabolism in Humans

The effects of insulin deprivation and replacement on adipose tissue metabolism were investigated in vivo with microdialysis in nine insulin-dependent diabetic patients with no residual insulin secretion. Dialysis probes, implanted in abdominal subcutaneous fat, were continuously perfused, and tissue dialysate concentrations of glycerol (lipolysis index), glucose, lactate, and pyruvate were determined. Comparisons were made with respective metabolite levels in venous plasma. After termination of intravenous insulin infusion, free insulin in plasma fell from 130 to 70 pM. At the same time, glucose levels in plasma and adipose tissue rose in parallel. However, the relative increase in glucose levels was greater in adipose tissue than in blood. On the other hand, the increase in glycerol concentration in adipose tissue (35%) was markedly < that in venous plasma (250%). Lactate and pyruvate levels in adipose tissue and blood remained unchanged. After the resumption of intravenous insulin, free insulin in plasma rose to ∼600 pM. At the same time, the glucose levels in blood and adipose tissue decreased rapidly, and the glycerol concentration in these tissues decreased to 50% of the baseline levels. The lactate and pyruvate levels in subcutaneous tissue increased briefly after insulin replacement, whereas the lactate but not pyruvate levels in blood showed a similar increase. The α- or β-blocking agents phentolamine and propranolol in the ingoing tissue perfusate did not influence tissue glycerol at any time during the experiment. We concluded that insulin-induced changes in circulating metabolites only partly reflect variations in adipose tissue substrate kinetics. During insulin deprivation, glucose is accumulated in the adipose tissue extracellular compartment, probably because of reduced utilization by the adipocytes. The increase in lactate and pyruvate levels in adipose tissue after insulin replacement may be explained by local metabolite production. The lipolytic activity in abdominal subcutaneous adipose tissue is only modestly enhanced during relative insulin deficiency, which is in contrast to overall lipolytic activity. Finally, adrenergic mechanisms do not seem to be involved in the changes in the lipolysis rate, which are induced by hypoinsulinemia and hyperinsulinemia.

Improved glucose metabolism after gastric bypass: evolution of the paradigm

BACKGROUND Glucose metabolism is improved in patients with type 2 diabetes after Roux-en-Y gastric bypass (RYGB). OBJECTIVES To quantify the relative contribution of calorie restriction, rerouting of nutrients, and adipose tissue reduction. SETTING University Hospital. METHODS Fifteen diabetic patients, (47±9 yr, body mass index 41.3±4.2 kg/m2) were randomized to a 2-week very low-calorie diet (VLCD) regimen or normal diet before RYGB. A euglycemic-hyperinsulinemic clamp, indirect calorimetry, and a standard meal test were performed prediet, postdiet (preoperatively), and 2 weeks and 12 months postoperatively. The primary outcome was whole-body insulin sensitivity (M) measured with the clamp 2 weeks postoperatively. RESULTS In the VLCD group, after 2 weeks of calorie restriction, M improved (2.9±1.3 to 4.2±1.1 mg/kg/min, P = .005) with no further change at 2 weeks postoperatively. In the normal diet group 2 weeks postoperatively, M was similar to the VLCD group (4.7±1.7 versus 4.2±1.1, P = .61). One year postoperatively, M improved further in both groups. The improvement in insulin-stimulated glucose uptake after VLCD and RYGB was entirely accounted for by nonoxidative glucose disposal (NOGD), whereas weight loss at 1 year postoperatively was associated with an increase in NOGD and glucose oxidation. Postprandial glucose improved after VLCD (P<.05) and even more 2 weeks after RYGB (P<.05) with no further change after 1 year. CONCLUSION Improved whole-body insulin sensitivity and postprandial glucose response occur early after RYGB. Low calorie intake and rerouting of nutrients contribute through distinct mechanisms. Weight loss contributes by increasing whole-body insulin sensitivity, including glucose oxidation and NOGD. These data suggest that the combination of different mechanisms is what makes RYGB an effective intervention for type 2 diabetes.

Microdialysis for the Assessment of Catecholamine-Induced Lipolysis in Adipose and Skeletal Muscle Tissue

Publisher Summary In recent times in situ techniques for studies of regional adipose tissue lipolysis have been developed, such as the arteriovenous-metabolite difference technique over a subcutaneous fat depot and the microdialysis technique. Microdialysis also has been introduced for studies of skeletal muscle tissue as well as several other tissues in the body. The major regulatory hormones for human adipose tissue lipolysis are insulin and catecholamines, which act on hormone-sensitive lipase. Binding sites for all adrenoceptor subtypes have been found in fat cells. It has to be pointed out that, with microdialysis, only one of the end-products of lipolysis, glycerol, can be monitored. Free fatty acids (FFAs) are hydrophobic and not dialyzable with the presently used membranes. As glycerol is not reutilized by adipose tissue, it is considered an index of lipolysis. The evaluation of blood flow variations in conjunction to in situ glycerol measurements is an important aspect. This is because the interstitial concentration of a metabolite can be determined both by its production and uptake in the tissue and by the transportation away or delivery to the tissue by the capillary bloodstream. The content of the dialysis sample reflects the net sum of these events. Tissue blood flow can be estimated either by Xenon-133 washout or by addition of a flow marker (for example, ethanol) to the microdialysis perfusate solvent. The microdialysis technique can be used in various types of lipolysis studies such as mechanistic in situ studies, systemic hormonal challenge, combinations of mechanistic in situ studies and systemic hormonal challenge, hormonal interactions, and in investigations of various tissues.