Nicotine infusion acutely impairs insulin sensitivity in type 2 diabetic patients but not in healthy subjects

OBJECTIVES

The aim of this study was to examine if an acute nicotine infusion alters insulin sensitivity to a similar degree in type 2 diabetic patients as in healthy control subjects.

DESIGN

. Double-blind, cross-over, placebo-controlled, randomized experimental study. Nicotine 0.3 microg kg-1 min(-1) or NaCl was infused (2 h) during a euglycaemic hyperinsulinaemic clamp (4 h) to assess insulin sensitivity.

SETTING

University research laboratory.

SUBJECTS

Six male and female type 2 diabetic patients [DM2; age 54 +/- 10 (mean +/- SD) years; body mass index (BMI) 25.6 +/- 2.9 kg m(-2)] treated with diet or one oral hypoglycaemic agent and six age- and BMI-matched control subjects (Ctr).

MAIN OUTCOME MEASURE

Insulin sensitivity (rate of glucose infusion per kg fat free body mass and minute), nicotine and free fatty acid (FFA) levels, pulse rate and blood pressure.

RESULTS

The infusions produced similar nicotine levels in both groups. In the absence of nicotine, DM2 were more insulin resistant than Ctr (6.7 +/- 0.4 vs. 10.9 +/- 0.3 mg kg-1 LBM min(-1), respectively; P < 0.0001). This insulin resistance was further aggravated by the nicotine infusion in DM2 but not in Ctr (4.6 +/- 0.3 vs. 10.9 +/- 0.3 mg kg(-1) LBM min(-1); P < 0.0001). Only minor differences were seen in FFA levels, pulse rates and blood pressure.

CONCLUSIONS

At this low infusion rate, nicotine aggravated the insulin resistance in DM2 but not in Ctr. This finding may be because of the (dysmetabolic) diabetic state per se or to an increased sensitivity to environmental factors associated with a genetic predisposition for type 2 diabetes. These results show that diabetic subjects are particularly susceptible to the detrimental effects of nicotine.

No difference in the lipolytic response to beta-adrenoceptor stimulation in situ but a delayed increase in adipose tissue blood flow in moderately obese compared with lean men in the postexercise period

This study was undertaken to determine the effect of previous exercise on adipose tissue responsiveness to beta-adrenoceptor stimulation and on adipose tissue blood flow (ATBF). Eight lean and 8 obese men (body mass index [BMI], 23.6 +/- 2.1 [SD] v 29.0 +/- 1.9 kg x m(-2)) were investigated with abdominal subcutaneous microdialysis and 133Xe clearance. A stepwise isoprenaline infusion (10(-8), 10(-7), and 10(-6) mol x L(-1)) was administered in situ in the microdialysis catheter before and 2 hours after a submaximal exercise bout (90 minutes of cycling at 55% of maximal O2 uptake). No differences in the response (increase in interstitial glycerol v preinfusion level) to isoprenaline infusions were found between the 2 groups. In both groups, there was no difference in the response to postexercise versus preexercise infusion. When the vasodilating agent hydralazine (0.125 g x L(-1)) was infused into the microdialysis catheter to control for the vascular effects of isoprenaline, an interaction effect between exercise and isoprenaline dose was found. Analyses showed an attenuated response to the high isoprenaline dose after exercise (lean, 251 +/- 42 [SE] micromol x L(-1); obese, 288 +/- 77 micromol x L(-1)) versus before exercise (lean, 352 +/- 62 micromol x L(-1), P = .045 v after; obese, 380 +/- 94 micromol x L(-1), P = .021 v after), indicating a desensitization of lipolysis to beta-adrenoceptor stimulation. ATBF and arterial plasma glycerol increased after exercise in both groups, but the increase was delayed in obese subjects. Arterial plasma insulin was higher in the obese versus lean subjects at all times, and decreased during recovery in both groups. In conclusion, abdominal subcutaneous adipose tissue responsiveness to beta-stimulation is not enhanced postexercise in lean and obese men, whereas previous exercise increases ATBF. Furthermore, the data suggest slower lipid mobilization postexercise and resistance to the antilipolytic effect of insulin in the obese.

Low cellular IRS 1 gene and protein expression predict insulin resistance and NIDDM

We examined the gene and protein expression of IRS 1 (insulin receptor substrate 1) in adipocytes from two groups of healthy individuals with an increased propensity for non-insulin-dependent diabetes mellitus (NIDDM): those with two first-degree relatives with diabetes and another group with massive obesity. A low expression of IRS 1 (</=50% of the matched control group) was seen in approximately 30% of both groups and these individuals were characterized by insulin resistance and its hallmarks: higher levels of insulin, glucose, and triglycerides. Two individuals with previously unknown NIDDM were diagnosed and both had low IRS 1 expression. Low IRS 1 protein expression was associated with low mRNA levels but not with the common Gly972Arg polymorphism of the IRS 1 gene. Taken together, our present and previous findings show that a low expression of IRS 1 in fat cells predicts insulin resistance and NIDDM. Furthermore, they support the likelihood that an impaired transcriptional activation may play a key role in the pathogenesis of NIDDM.-Carvalho, E., Jansson, P.-A., Axelsen, M., Eriksson, J. W., Huang, X., Groop, L., Rondinone, C., Sjöström, L., Smith, U. Low cellular IRS 1 gene and protein expression predict insulin resistance and NIDDM.

Validation of the internal reference technique for microdialysis measurements of interstitial histamine in the rat

The internal reference technique (IRT) was compared with the no net flux method (NFM) as a microdialysis calibration technique for sampling of interstitial histamine in the rat. Microdialysis catheters (polyacrylonitrile, 50 kD cut off) were inserted in liver, muscle, subcutaneous tissue and in an induced adenocarcinoma. Estimated relative recovery with IRT ranged from 23+/-2% in liver to 30+/-3% in subcutaneous tissue with and without tumor (p<0.05). By using the NFM-technique we found similar recovery as compared to the IRT in all tissues studied. Interstitial histamine was up to 3-fold higher than the mean plasma histamine concentration (54+/-2 nmol/l). Subcutaneous tissue (177+/-39 nmol/l) and subcutaneous tumor (165+/-29 nmol/l) exhibited high histamine while liver (65+/-14 nmol/l) and liver tumor (75+/-7 nmol/l) had low interstitial histamine concentrations. In conclusion, the IRT was validated against the NFM as a rapid method for histamine measurements in situ in the rat.

Insulin signaling and action in fat cells: associations with insulin resistance and type 2 diabetes

Adipose tissue only accounts for a relatively small proportion (< 10%) of the peripheral glucose utilization in response to insulin. However, the fat cells may still play an important role in insulin resistance and Syndrome X through, for instance, its endocrine functions (production of leptin, TNF alpha, PAI-1, etc.) and involvement in lipid metabolism (FFA release and hydrolysis of triglycerides). The fat cells are also highly sensitive to insulin and may thus be used to elucidate molecular mechanisms for insulin resistance in man. Examinations of the intracellular signaling mechanisms for insulin in fat cells from individuals with Type 2 diabetes revealed markedly lower insulin-stimulated PI3-kinase activity. This was due to a pronounced reduction in the cellular expression of the docking protein, IRS 1, whereas expression of IRS 2 was normal. However, IRS 2-associated PI3-kinase activity was only approximately one-third of that found to be associated with IRS 1 in normal cells. Downstream activation and serine phosphorylation of PKB/Akt by insulin were also markedly reduced in Type 2 diabetes. Furthermore, the dose-response curve for this effect of insulin was similar to that for glucose transport in both normal and Type 2 diabetic cells. Thus, these data show that both PI3-kinase and PKB activation by insulin are markedly reduced in Type 2 diabetes. We also examined whether an attenuated activation of PI3-kinase by insulin can be seen in non-diabetic insulin-resistant states. Approximately 30% of healthy subjects with at least two first-degree relatives with Type 2 diabetes exhibited perturbations in IRS-1 expression and signaling. These individuals were characterized by insulin resistance as well as other markers of Syndrome X. Thus, impaired IRS-1 expression and downstream signaling events in fat cells in response to insulin are associated with insulin resistance and Syndrome X.

Glucose turnover and adipose tissue lipolysis are insulin-resistant in healthy relatives of type 2 diabetes patients: is cellular insulin resistance a secondary phenomenon?

To elucidate potential mechanisms for insulin resistance occurring early in the development of type 2 diabetes, we studied 10 young healthy individuals, each with two first-degree relatives with type 2 diabetes, and 10 control subjects without known type 2 diabetic relatives. They were pairwise matched for age (35 +/- 1 vs. 35 +/- 1 years), BMI (23.6 +/- 0.6 vs. 23.1 +/- 0.4 kg/m2), and sex (four men, six women). Glucose turnover was assessed during a euglycemic clamp at two insulin levels (low approximately 20 mU/l; high approximately 90 mU/l), and abdominal subcutaneous adipose tissue (SAT) lipolysis and blood flow were concomitantly studied with microdialysis and 133Xe clearance. HbA1c was higher in patients with type 2 diabetic relatives than in control subjects (4.8 +/- 0.1 vs. 4.5 +/- 0.1%, P < 0.02), but fasting glucose, insulin, and C-peptide levels were similar. During the clamp, the insulin sensitivity index for glucose disposal was lower (P < 0.03) in relatives than in control subjects (low 12.0 +/- 1.6 vs. 18.1 +/- 1.4; high 9.4 +/- 0.8 vs. 12.9 +/- 0.6 [100 x mg x l x kg(-1) x mU(-1) x min(-1)]). This difference was partially attributed to slightly higher clamp insulin levels in the relatives (P < 0.03), suggesting an impaired rate for insulin clearance. SAT lipolysis measured as in situ glycerol release did not differ under basal conditions (2.0 +/- 0.2 vs. 2.1 +/- 0.2 micromol x kg(-1) x min(-1)), but the suppression during the insulin infusion was less marked in relatives than in control subjects (glycerol release: low 0.92 +/- 0.09 vs. 0.68 +/- 0.16; high 0.71 +/- 0.10 vs. 0.34 +/- 0.10 micromol x kg(-1) x min(-1); P < 0.03). Plasma nonesterified fatty acids also tended to be higher in relatives than in control subjects during the insulin infusion (NS). In contrast, in vitro experiments with isolated subcutaneous adipocytes displayed similar effects of insulin in relatives and control subjects with respect to both glucose uptake and antilipolysis. In conclusion, insulin action in vivo on both lipolysis and glucose uptake is impaired early in the development of type 2 diabetes. Since this impairment was not found in isolated adipocytes, it may be suggested that neural or hormonal perturbations precede cellular insulin resistance in type 2 diabetes.

Lactate and glycerol release from subcutaneous adipose tissue in black and white lean men

To measure interstitial glycerol and lactate production from the sc adipose tissue of two regions in nine black and nine white lean men, sc microdialysis was performed in combination with adipose tissue blood flow rates measured with 133Xe clearance. In the postabsorptive state, the plasma glucose and insulin levels of the black men and white men were similar. The black men had higher plasma free fatty acids (825+/-97 vs. 439+/-58 micromol/L; P < 0.005), glycerol (99.5+/-5.1 vs. 54.1+/-3.3 micromol/L; P < 0.0001), and lactate (1056+/-95 vs. 729+/-45 micromol/L; P < 0.01). Interstitial glycerol concentrations in the black and white men were 227 vs. 163 micromol/L (P < 0.01) and 230 vs. 162 micromol/L (P < 0.05) in the abdominal and femoral regions. The adipose tissue blood flow rate was higher in the black men in the abdominal (7.9+/-0.9 vs. 3.1+/-0.5 mL/100 g x min; P < 0.01) and femoral area (5.2+/-0.6 vs. 2.8+/-0.3; P < 0.01). Interstitial lactate concentrations in black and white men were 1976 vs. 1364 micromol/L (P < 0.004) and 1953 vs. 1321 micromol/L (P < 0.004) in the abdominal and femoral regions, respectively. Glycerol release was higher in black men vs. white men for abdominal (0.21+/-0.02 vs. 0.14+/-0.02 micromol/100 g x min; P < 0.02) and femoral (0.22+/-0.02 vs. 0.15+/-0.01; P < 0.05) areas. Postprandially, black men had higher plasma glucose levels [1 h, 9.6+/-0.4 vs. 8.2+/-0.5 mmol/L (P < 0.05); 2 h, 8.9+/-0.4 vs. 7.2+/-0.4 mmol/L (P < 0.01)], but lower plasma insulin levels [1 h, 173+/-13 vs. 264+/-48 pmol/L (P < 0.05); 2 h, 136+/-20 vs. 209+/-34 pmol/L (P < 0.05)]. Plasma free fatty acid, lactate, and glycerol levels remained higher in the black men. After 1 h, lactate release was higher in the black men vs. that in the white men for abdominal (20.5+/-1.6 vs. 14.7+/-2.5 micromol/100 g x min;P < 0.05) and femoral (15.6+/-1.1 vs. 12.1+/-1.8; P < 0.03) areas. We conclude that the black men, who are relatively insulinopenic postprandially, have a brisker lipolysis and also release more lactate from sc fat tissue than white men. These differences in adipose tissue metabolism may be related to differences in the lipid profiles and glucose metabolism previously documented in these ethnic groups.

Postprandial hypertriglyceridemia and insulin resistance in normoglycemic first-degree relatives of patients with type 2 diabetes

BACKGROUND

Impaired ability to eliminate lipids in the postprandial state is an atherogenic trait associated with insulin resistance.

OBJECTIVE

To assess insulin sensitivity and postprandial triglyceride metabolism in prediabetic persons.

DESIGN

Cross-sectional study.

SETTING

Sahlgrenska University Hospital, Göteborg, Sweden.

PARTICIPANTS

13 healthy, normotriglyceridemic men with two first-degree relatives with type 2 diabetes and 13 carefully matched controls without known diabetes heredity.

MEASUREMENTS

Oral glucose tolerance test, insulin sensitivity (euglycemic clamp technique), and fasting and postprandial triglyceride levels after a mixed meal.

RESULTS

Relatives of persons with type 2 diabetes were insulin resistant but had normal glucose tolerance. They exhibited postprandial hypertriglyceridemia; the 6-hour triglyceride incremental area under the curve was 50% higher than that of the control group (P = 0.037).

CONCLUSIONS

These healthy male first-degree relatives of patients with type 2 diabetes are insulin resistant and exhibit postprandial lipid intolerance despite having normal fasting triglyceride levels. These characteristics, which occur in the absence of glucose intolerance, are associated with an increased risk for macroangiopathy.

Relationship between blood pressure, metabolic variables and blood flow in obese subjects with or without non-insulin-dependent diabetes mellitus

BACKGROUND

To assess the relationship between systemic blood pressure, metabolic variables and adipose tissue blood flow, we studied 55 subjects before and 36 subjects after an oral glucose load (100 g).

METHODS

The subjects were divided into four different groups: (a) young lean control subjects [age 31 +/- 1 years, mean +/- SE, BMI (body mass index) 22.7 +/- 0.4 kg m-2]; (b) young obese subjects (age 29 +/- 2 years, BMI 37.8 +/- 1.8 kg m-2); (c) middle-aged obese subjects (age 50 +/- 2 years, BMI 30.2 +/- 0.9 kg m-2); and (d) middle-aged obese non-insulin-dependent diabetic (NIDDM) subjects (age 54 +/- 2 years, BMI 30.0 +/- 0.7 kg m-2).

RESULTS

Groups 2-4 demonstrated a low fasting adipose tissue blood flow (ATBF) and the increase in ATBF after oral glucose was impaired. A further impairment was present in NIDDM subjects. Systolic and diastolic blood pressure were also increased in groups 2-4 and further so in group 4. Fasting glucose, lactate and free fatty acid (FFA) levels correlated positively with the systolic blood pressure, whereas ATBF correlated negatively with the diastolic blood pressure. Furthermore, in the NIDDM subjects fasting lactate correlated closely with both the systolic (r = 0.649, P = 0.01) and diastolic (r = 0.626, P = 0.013) blood pressure.

CONCLUSION

These data suggest a close relationship between insulin resistance and regulation of adipose tissue blood flow as well as blood pressure.

Experiences of the 14C-ethanol technique for blood flow measurements in human subcutaneous adipose tissue

We compared the 14C-ethanol technique and 133Xe-clearance for adipose tissue blood flow measurements in young healthy subjects before and after exercise on an ergometer bicycle. The results showed a decrease in outflow/inflow ratio of 14C-ethanol during the basal situation before the exercise, indicating an increased blood flow. However, there was a great range of values, and no correlation between the 14C-ethanol technique and 133Xe-clearance was found. Our data indicate that the 14C-ethanol technique can not be recommended in its current form.

Peroxovanadate and insulin action in adipocytes from NIDDM patients. Evidence against a primary defect in tyrosine phosphorylation

We studied the effects of insulin and the stable peroxovanadate compound potassium bisperoxopicolinatooxovanadate (bpV(pic)), a potent inhibitor of phosphotyrosine phosphatases, on lipolysis and glucose uptake in subcutaneous adipocytes from 10 male patients with non-insulin-dependent diabetes mellitus (NIDDM) and 10 matched non-diabetic control subjects. Lipolysis stimulated by isoprenaline or the cAMP analogue, 8-bromo-cyclic AMP (8-br-cAMP), was reduced by approximately 40% in NIDDM compared to control subjects. In both groups bpV(pic) exerted an antilipolytic effect that was similar to insulin (approximately 50 % inhibition). 14C-U-glucose uptake was dose-dependently increased by bpV(pic) treatment, but this effect and also that of insulin were impaired in NIDDM compared to control (bpV(pic) 1.6-fold vs 2.4-fold and insulin 2.2-fold vs 3.4-fold). Furthermore, low concentrations of bpV(pic) did not affect insulin-stimulated glucose uptake, although tyrosine phosphorylation of the insulin receptor beta-subunit was clearly increased by bpV(pic). In conclusion, 1) beta-adrenergic stimulation of lipolysis in vitro is attenuated in NIDDM adipocytes due to post-receptor mechanisms. 2) Both insulin and bpV(pic) decrease lipolysis and enhance glucose uptake in control as well as NIDDM adipocytes. The effect on glucose uptake, but not that on lipolysis, is impaired in NIDDM cells. 3) Peroxovanadate does not improve sensitivity and responsiveness to insulin in NIDDM adipocytes, showing that insulin-resistant glucose uptake in NIDDM is not overcome by phosphotyrosine-phosphatase inhibition and, thus, probably is not caused by impaired tyrosine phosphorylation events alone.

Strategies toward improved control during insulin lispro therapy in IDDM. Importance of basal insulin

OBJECTIVE

To examine whether overall glycemic control can be improved with insulin lispro by adjustment of the basal insulin regimen without an increased risk of hypoglycemia.

RESEARCH DESIGN AND METHODS

A 5-month open study was performed in 66 IDDM patients after they had been transferred from human regular insulin to insulin lispro as a premeal therapy. The premeal and basal insulin regimens were adjusted according to self-monitoring of blood glucose during the visits at 2-week to 1-month intervals. Diurnal glucose profile, hypoglycemic events, HbA1c, and patient satisfaction were evaluated.

RESULTS

The mean daily glucose level decreased from 9.2 +/- 0.2 to 8.4 +/- 0.2 mmol/l (P = 0.001) and HbA1c decreased from 8.8 +/- 0.1 to 8.0 +/- 0.1% (P < 0.001) (mean +/- SD). The number of daily NPH injections increased from 1.4 +/- 0.1 at baseline to 3.1 +/- 0.1 at the end of the study. Total daily insulin dose increased by 3 U (7%) because of an 8-U (43%) rise in basal insulin, whereas premeal insulin dose decreased by 5 U (20%). The number of hypoglycemic episodes did not change during the study. Of the patients, 86% considered insulin lispro equal or better than human regular insulin.

CONCLUSIONS

Although the study was open, the date suggest that the appropriate combination of insulin lispro and basal insulin can improve postmeal hyperglycemia, HbA1c, and treatment satisfaction without increasing the risk of hypoglycemia.

Insulin sensitivity following treatment with the alpha 1-blocker bunazosin retard and the beta 1-blocker atenolol in hypertensive non-insulin-dependent diabetes mellitus patients

OBJECTIVE

To compare the effects of the alpha 1-blocker bunazosin retard and the beta 1-blocker atenolol (Uniloc) on insulin sensitivity and glucose and lipid homeostasis in patients with type-2 diabetes and hypertension.

METHODS

Patients with controlled type-2 diabetes (non-insulin-dependent diabetes mellitus), treated by diet or oral sulphonylurea derivatives, and with mild-to-moderate hypertension were include in a randomized, parallel group, double-blind, multicentre study. After a single-blind placebo run-in period lasting 4-6 weeks, the patients were treated either with bunazosin retard or with atenolol for a further 16 weeks including an initial dose titration period to achieve blood pressure control. Treatment involved 3, 6 or 12 mg bunazosin retard tablets or 25, 50 or 100 mg atenolol tablets, administered orally once a day and prescribed according to blood pressure response. The euglycaemic hyper-insulinaemic clamp technique was used to assess insulin sensitivity both after the placebo period and after the active treatment. A total of 95 patients was enrolled in the study (placebo phase). Forty-eight patients were withdrawn from the placebo phase, mainly due to their blood pressures being outside the required range (seated diastolic blood pressure 90-114 mmHg) and 47 patients were allocated randomly to active treatment. Of these, 23 were administered bunazosin retard and 24 atenolol. All evaluations were on an intention-to-treat basis.

RESULTS

Insulin sensitivity assessed as glucose utilization during the clamp was significantly higher following bunazosin retard compared with following atenolol administration (3.52 +/- 0.27 versus 2.86 +/- 0.19 units of metabolic clearance rate of glucose index, P < 0.05). The insulin level attained during clamps (infusion rate 56 mU/m2 per min) was higher (P < 0.05) following atenolol (117 +/- 5 mU/l) than it was following bunazosin retard administration (102 +/- 5) or placebo (108 +/- 3), possibly due to an impaired insulin clearance. Compared with placebo, atenolol treatment resulted in significantly increased glucosylated haemoglobin whereas bunazosin retard had no significant effect. The two drugs did not show any consistent differences in lipid profile or fibrinogen and plasminogen activator inhibitor 1 levels. During the study seven serious adverse events were reported and one was reported shortly after completion of the study. All except one were classified as not related to the study drug and five of them occurred during placebo treatment. The non-serious side effects were in general considered to be either unrelated to the test drugs or expected effects of the two respective drug classes. Both bunazosin retard and atenolol displayed acceptable safety profiles.

CONCLUSION

Bunazosin retard treatment in hypertensive non-insulin-dependent diabetes mellitus patients appears to be associated with a slightly higher insulin sensitivity than is atenolol.

Glutamine and alanine metabolism in NIDDM

Gluconeogenesis is increased in NIDDM. We therefore examined the metabolism of glutamine and alanine, the most important gluconeogenic amino acids, in 14 postabsorptive NIDDM subjects and 18 nondiabetic volunteers using a combination of isotopic ([6-3H]glucose (20 microCi, 0.2 microCi/min), [U-14C]glutamine (20 microCi, 0.2 microCi/min), [3-13C]alanine (99% 13C, 2 mmol, 20 micromol/min), [ring-2H5]phenylalanine (99% 2H, 2 micromol/kg, 0.03 micromol x kg(-1) x min(-1)), and limb balance techniques. Alanine turnover (4.54 +/- 0.24 vs. 5.64 +/- 0.33 micromol x kg(-1) x min(-1)), de novo synthesis (3.00 +/- 0.25 vs. 4.01 +/- 0.33 micromol x kg(-1) x min(-1)), and conversion to glucose (1.02 +/- 0.09 vs. 1.56 +/- 0.17 micromol x kg(-1) x min(-1)) were increased in NIDDM subjects (all P < 0.01), while its forearm release (0.45 +/- 0.04 vs. 0.39 +/- 0.04 micromol x kg(-1) x min(-1)) was unaltered. Although glutamine turnover (4.81 +/- 0.23 vs. 4.40 +/- 0.31 micromol x kg(-1) x min(-1)) was unaltered in NIDDM, its conversion to glucose (0.57 +/- 0.04 vs. 1.08 +/- 0.10 micromol x kg(-1) x min(-1)) and to alanine (0.10 +/- 0.01 vs. 0.34 +/- 0.04 micromol x kg(-1) x min(-1)) (both P = 0.001) was increased while its oxidation (2.84 +/- 0.27 vs. 1.84 +/- 0.15 micromol x kg(-1) x min(-1), P = 0.03) and forearm release (0.77 +/- 0.05 vs. 0.62 +/- 0.09 micromol x kg(-1) x min(-1), P < 0.008) were both reduced. Our results thus demonstrate that there are substantial alterations of glutamine and alanine metabolism in NIDDM. Conversion of both amino acids to glucose and the proportion of their turnover used for gluconeogenesis are increased; release of both amino acids from tissues other than skeletal muscle seems to be increased. Finally, the reduction in glutamine oxidation, possibly the result of competition with glucose and free fatty acids as fuels, makes more glutamine available for gluconeogenesis without a change in its turnover.

Microdialysis measurements in skin: evidence for significant lactate release in healthy humans

To assess net lactate release from dermal skin, seven lean, healthy men were studied after overnight fasting. Two microdialysis catheters were inserted in the upper dermal tissue, as ensured by ultrasound scanning, in the periumbilical area. Each catheter was calibrated in situ to get an estimate of the lactate concentration in interstitial fluid (1,001 +/- 24 mumol/l), which in turn enabled calculation of the local capillary-venous lactate concentration (963 +/- 25 mumol/l). Concomitantly, arterialized venous plasma lactate (673 +/- 32 mumol/l), blood hematocrit (43 +/- 1%), and skin blood flow (3.8 +/- 0.9 ml.100 g-1.min-1) as measured by 133Xe clearance were determined, and dermal apparent lactate release (570 +/- 89 nmol.100 g-1.min-1) was estimated according to the Fick principle. During an oral glucose tolerance test (OGTT, 75 g), the dermal interstitial-arterial lactate difference decreased significantly to reach a nadir at 60 min. Moreover, no significant increase in skin blood flow was seen during the OGTT. In conclusion, we found a significant net lactate release from abdominal dermal skin after overnight fasting, whereas no significant increase was observed during an OGTT.

Microdialysis methodology for the measurement of dermal interstitial fluid in humans

In this study we aimed to validate the microdialysis technique for metabolic measurements in the dermal interstitial fluid. The abdominal and forearm skin was used for microdialysis in 15 healthy normal weight volunteers. The depth of the microdialysis catheter was assessed by ultrasound measurement. Structural impairment and blood flow were judged from biopsies and from laser Doppler measurements taken adjacent to the catheters. Dermal interstitial lactate and pyruvate concentrations were measured, under steady state fasting conditions, after equilibrium calibration of each catheter in situ. The dermal interstitial glucose concentration was estimated by means of the retrodialysis calibration method, which has previously not been evaluated for skin microdialysis. The mean catheter depth (+/- standard deviation) was 0.8 +/- 0.3 mm. Small areas of localized bleeding, but no inflammatory reaction, was found surrounding the catheters. The perfusion in the microdialysis region was slightly increased (15-25%). The lactate/pyruvate ratio (12 +/- 0.7) showed non-ischaemic values. The dermal interstitial lactate concentration was significantly higher (1171 +/- 228 mumol/l) than the plasma lactate (781 +/- 180 mumol/l), indicating an ongoing nonoxidative glucose metabolism. Retrodialysis calibration correctly estimated the dermal glucose level to be similar to that in plasma, which may indicate the usefulness of this calibration method for microdialysis studies of endogenous substrates in the dermal interstitial fluid.

The effect of metformin on adipose tissue metabolism and peripheral blood flow in subjects with NIDDM

OBJECTIVE

To examine the effect of metformin on net lactate and glycerol release in NIDDM subjects, we used abdominal subcutaneous microdialysis combined with 133Xe clearance. Skeletal muscle blood flow (MBF) was assessed simultaneously both before and after metformin treatment.

RESEARCH DESIGN AND METHODS

Nine male patients with NIDDM (age 53 +/- 2 years [mean +/- SE]; BMI 30.2 +/- 1.4 kg/m2; body fat 23.0 +/- 2.6 kg; diabetes duration 4.6 +/- 1.5 years; six of nine receiving sulfonylurea treatment) were recruited into an open study. They were studied after an overnight fast, both before and after 1 week of additional treatment with 500 mg metformin three times daily. Nine weight- and age-matched nondiabetic subjects served as a control group.

RESULTS

Postabsorptive net subcutaneous lactate release increased (149 +/- 50 vs. 475 +/- 127 nmol.100 g-1.min-1, P < 0.05) whereas plasma lactate was unchanged after metformin treatment in the NIDDM patients. The net decrease of glycerol release 90 min after an oral glucose tolerance test was more pronounced (110 +/- 30 vs. 199 +/- 20 nmol.100 g-1.min-1, P < 0.05) after metformin treatment. Both adipose tissue blood flow (ATBF) (1.5 +/- 0.1 vs. 2.3 +/- 0.2 ml.100 g-1.min-1, P < 0.01) and MBF (3.2 +/- 0.4 vs. 4.2 +/- 0.5 ml.100 ml-1.min-1, P < 0.05) increased after metformin treatment.

CONCLUSIONS

In this open study, postabsorptive net lactate release in abdominal subcutaneous adipose tissue was clearly increased in NIDDM patients after metformin treatment. Basal ATBF as well as MBF was improved after metformin treatment. Whether this reflects enhanced metabolic control or is a drug-specific effect remains to be established.

Microdialysis assessment of adipose tissue metabolism in post-absorptive obese NIDDM subjects

Lactate and glycerol turnover is enhanced in obesity and NIDDM. To evaluate the influence of NIDDM on subcutaneous adipose tissue metabolism microdialysis combined with 133Xe clearance and measurements in arterialized plasma were carried out using samples of subcutaneous abdominal fat from nine obese NIDDM subjects (glucose, 7.9 +/- 0.7 mmol L-1) (mean +/- SEM) and nine obese non-diabetic subjects (glucose, 4.9 +/- 0.1) matched for age, BMI and body fat. After an overnight fast arterialized plasma levels were 1145 +/- 110 vs. 876 +/- 59 mumol L-1 (P < 0.05) for lactate and 75 +/- 10 vs. 66 +/- 8 mumol L-1 for glycerol in the diabetic and control group, respectively. The corresponding abdominal subcutaneous interstitial lactate and glycerol concentrations were 1278 +/- 63 vs 1107 +/- 64 mumol L-1 and 314 +/- 28 vs. 311 +/- 17 mumol L-1, respectively. However, adipose tissue blood flow in the same region was lower in NIDDM subjects (1.5 +/- 0.2 vs 2.4 +/- 0.3 mL 100 g-1 min-1) (P < 0.05). Consequently, apparent subcutaneous lactate and glycerol release, estimated according to Fick, were not statistically different in the two groups (1.8 +/- 0.4 vs 2.4 +/- 0.8 and 2.1 +/- 0.4 vs 3.1 +/- 0.5 mumol kg-1 min-1 in NIDDM and control subjects, respectively). Thus, in the post-absorptive state apparent lactate and glycerol release by the abdominal subcutaneous tissue in obese NIDDM subjects was similar to that in a matched group of obese non-diabetic controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the sympathetic nervous system on insulin sensitivity and adipose tissue metabolism: a study in spinal cord-injured subjects

To evaluate insulin sensitivity and adipose tissue metabolism, seven spinal cord-injured (SCI) subjects (age, 43 +/- 6 years; body mass index, 22.8 +/- 1.4; mean +/- SE) and their seven siblings (age, 45 +/- 6 years; body mass index, 24.8 +/- 0.8) were studied using oral glucose (100-g) tolerance tests (OGTTs), euglycemic insulin clamps (insulin infusion, 1 mU/kg.min), and microdialysis of the subcutaneous tissue. Blood glucose and insulin after oral glucose were significantly increased in SCI subjects as compared with their siblings. During insulin clamping, plasma adrenaline increased significantly in controls, but not in SCI subjects. However, the rates of glucose production (2.02 +/- 0.36 v 1.59 +/- 0.09 mg/kg.min) and utilization (5.13 +/- 0.71 v 5.78 +/- 0.34) were similar in the two groups. Furthermore, interstitial subcutaneous glycerol and lactate concentrations before and after oral glucose were similar in the two groups, even in neurally decentralized tissue with broken connection between the central nervous system and peripheral sympathetic nerves. The data suggest that (1) well-mobilized SCI subjects show minor insulin resistance, and (2) sympathetic nervous activity has a minor influence on adipose tissue metabolism in the postabsorptive state, but may affect insulin sensitivity during euglycemic clamping.

Comparison of two methods to assess the tissue/blood partition coefficient for xenon in subcutaneous adipose tissue in man

A new method to calculate the tissue/blood partition coefficient (lambda) for xenon in studies on the subcutaneous adipose tissue blood flow was compared with a previously reported method based on local skinfold thickness (lambda LST). The former method included needle biopsies from the abdominal and femoral subcutaneous adipose tissue, and the mean fat cell diameter was measured (lambda ECT). The extracellular tissue fraction in subcutaneous tissue was then estimated from a diagram. The tissue lipid content was approximated to equal the relative intracellular volume and Ostwald's solubility coefficients for 133Xe, based on the distribution of xenon in lipid, albumin and 0.9% saline were applied. Estimated lambda-values based on needle biopsies from the abdominal site were: 8.6 +/- 0.1 versus 9.9 +/- 0.4 ml g-1 (mean +/- SE) (P < 0.05) and from the femoral site: 9.1 +/- 0.1 versus 9.6 +/- 0.2 in lean (n = 10) and obese subjects (n = 10), respectively. The corresponding lambda-values obtained from skinfold measurements were: 6.2 +/- 0.5 versus 11.0 +/- 0.4 (P < 0.001) and 6.9 +/- 0.3 versus 11.4 +/- 0.4 (P < 0.001) in lean and obese subjects, respectively. Pooled lambda LST-values correlated positively with estimated adipose tissue blood flow (ATBF) (r: 0.34, P < 0.05, n = 40) whereas no such correlation was found for lambda ECT-values. In conclusion, a new method is presented which may allow an accurate determination of, and which may lead to reliable data on, subcutaneous ATBF in both lean and obese subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hyperglycemia on in vivo adipose tissue metabolism studied with microdialysis in IDDM subjects

The effect of hyperglycemia on in vivo adipose tissue metabolism was studied with microdialysis in seven lean patients with insulin-dependent diabetes mellitus (IDDM) receiving a constant infusion of insulin (36 pmol.m-2.min-1). Glucose was infused in a randomized fashion to maintain either a lower glucose level (6.6 +/- 0.3 mM, mean +/- SE) or hyperglycemia (11.8 +/- 0.8 mM) for 3 h. For insulin concentrations of 84 +/- 12 and 96 +/- 12 pM, hyperglycemia (11.8 +/- 0.8 mM) did not alter the plasma glycerol or lactate levels significantly but resulted in a significant (P < 0.0001) increase in plasma free fatty acid levels (0.49 +/- 0.13 vs. 0.32 +/- 0.08 mM). Plasma catecholamine levels were unchanged during hyperglycemia. Interstitial glycerol concentrations, measured in abdominal subcutaneous adipose tissue as an index of lipolysis, were not significantly influenced by hyperglycemia when compared with concentrations at the lower glucose level (92 +/- 30 vs. 106 +/- 18 microM). Moreover, hyperglycemia did not change abdominal adipose interstitial lactate levels significantly (1,248 +/- 174 vs. 1,351 +/- 159 microM during euglycemia). It may be concluded that hyperglycemia has no independent antilipolytic effect in IDDM subjects. Furthermore, in these patients, hyperglycemia gives no further lactate production in the subcutaneous adipose tissue in the presence of low physiological insulin levels.

Glycogen: its mode of formation and contribution to hepatic glucose output in postabsorptive humans

To assess the relative contributions of gluconeogenesis and glycogenolysis to overall hepatic glucose output in postabsorptive normal humans and those of the indirect and direct pathways for glycogen synthesis, we studied six normal volunteers, who had been fasted for 16 h to reduce their hepatic glycogen stores, and then ingested glucose (250 g over 10 h) enriched with [6-3H] glucose to replenish and label their hepatic glycogen. After a 10-h overnight fast, release of the [6-3H] glucose into the circulation was traced with [2-3H] glucose to estimate breakdown of glycogen that had been formed via the direct pathway while gluconeogenesis was simultaneously estimated by incorporation of infused [14C] lactate into plasma glucose. We found that release of [6-3H] glucose into plasma (6.79 +/- 0.69 mumol.kg-1.min-1) accounted for 46 +/- 5% of hepatic glucose output (15.0 +/- 0.7 mumol.kg-1.min-1) while glucose formed from lactate (2.71 +/- 0.28 mumol.kg-1.min-1) accounted for 19 +/- 2% of hepatic glucose output. Since these determinations underestimate direct pathway glycogenolysis and overall gluconeogenesis, a maximal estimate for the contribution of indirect pathway glycogenolysis to hepatic glucose output is obtained by subtracting the sum of direct pathway glycogenolysis and lactate gluconeogenesis from hepatic glucose output. This amounted to a maximum of 36 +/- 5% of hepatic glucose output and 44 +/- 6% of overall glycogenolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

An improved method to calculate adipose tissue interstitial substrate recovery for microdialysis studies

We simultaneously compared the conventional, time-consuming point of no net flux method for calculation of interstitial substrate recovery necessary for in vivo microdialysis studies with a simple isotopic method using rat epididymal fat pads. The recovery (%) calculated with the conventional method and the isotopic method for glucose (7.4 +/- 1.1 vs. 6.6 +/- 0.6), glycerol (23 +/- 4 vs. 26 +/- 5) and lactate (40 +/- 8 vs. 38 +/- 5), respectively, were not significantly different. Moreover, the overall correlation coefficient (N = 25) between the methods was 0.87, p < 0.001. We therefore conclude that the methods yield comparable results, and the more convenient isotopic method should become the method of choice for determining adipose tissue interstitial recovery for glucose, lactate and glycerol.