Macrophage gene expression in adipose tissue is associated with insulin sensitivity and serum lipid levels independent of obesity

OBJECTIVE

Obesity is linked to both increased metabolic disturbances and increased adipose tissue macrophage infiltration. However, whether macrophage infiltration directly influences human metabolism is unclear. The aim of this study was to investigate if there are obesity-independent links between adipose tissue macrophages and metabolic disturbances.

DESIGN AND METHODS

Expression of macrophage markers in adipose tissue was analyzed by DNA microarrays in the SOS Sib Pair study and in patients with type 2 diabetes and a BMI-matched healthy control group.

RESULTS

The expression of macrophage markers in adipose tissue was increased in obesity and associated with several metabolic and anthropometric measurements. After adjustment for BMI, the expression remained associated with insulin sensitivity, serum levels of insulin, C-peptide, high density lipoprotein cholesterol (HDL-cholesterol) and triglycerides. In addition, the expression of most macrophage markers was significantly increased in patients with type 2 diabetes compared to the control group.

CONCLUSION

Our study shows that infiltration of macrophages in human adipose tissue, estimated by the expression of macrophage markers, is increased in subjects with obesity and diabetes and associated with insulin sensitivity and serum lipid levels independent of BMI. This indicates that adipose tissue macrophages may contribute to the development of insulin resistance and dyslipidemia.

Decreased permeability surface area for glucose in obese women with postprandial hyperglycemia: no effect of phosphodiesterase-5 (PDE-5) inhibition

Insulin-mediated microvascular recruitment is recognized as a potential mechanism contributing to insulin resistance. In this study, we compared a marker of microvascular function, the permeability surface area for glucose (PS(glu)), and forearm glucose uptake after an OGTT in obese women with impaired glucose metabolism and healthy lean nondiabetic women, with the aim to characterize whether decreased permeability surface area for glucose or decreased glucose uptake may contribute to postprandial hyperglycemia in the obese group. In addition, we evaluated whether the phosphodiesterase-5 (PDE-5) inhibitor tadalafil, in a randomized double blind placebo controlled design, might attenuate postprandial glucose levels in obese women. For these purposes, intramuscular microdialysis, blood sampling from arterial and venous blood of the forearm, and measurements of forearm blood flow were performed. The results showed an impaired permeability surface area for glucose (IAUC PS(glu) 31±13 vs. 124±31; p<0.05) in obese when compared with lean participants, but no differences in forearm glucose uptake appeared between the groups. Furthermore, a single dose of tadalafil 10 mg showed no improvement of the permeability surface area for glucose, glucose uptake, or circulating glucose levels in obese participants. In conclusion, the postprandial PS(glu) response was impaired in obese women showing postprandial hyperglycemia, indicating a compromised microcirculation. However, we were unable to demonstrate any acute effect on either vascular function or glucose uptake of the phosphodiesterase-5 (PDE-5) inhibitor tadalafil.

Increased insulin secretion and decreased glucose concentrations, but not allostatic load, are associated with stress-related exhaustion in a clinical patient population

Allostatic load (AL) has been shown to be a useful marker of physiological strain during chronic stress and burnout in non-clinical working populations. The usability of the AL index for a clinical population with severe stress-related exhaustion was tested in this study. Thirteen biomarkers assembled as an AL index were analysed using blood samples from 90 patients with stress-related exhaustion (43 men and 47 women, age 31-61 years) and 90 healthy controls (46 men and 44 women, age 25-56 years). The AL scores did not differ between patients and controls. For men, some indication of higher cardiovascular risk was seen in the patient group: male patients had higher body mass index and waist-hip ratio and a poorer blood lipid status than male controls. We found lower plasma glucose concentrations in both female and male patients than those in controls. The male patients also showed increased fasting serum insulin concentrations. Further analysis using homeostasis model assessment for insulin resistance and β-cell function showed indications of insulin resistance in the patient group, particularly in the males, and an increased insulin secretion in both male and female patients. In conclusion, AL index does not seem to capture plausible physiological strain in patients diagnosed with stress-related exhaustion. The finding of lower plasma glucose concentrations, probably due to higher insulin secretion, in patients with severe stress-related exhaustion, needs to be further investigated, including mechanisms and the clinical relevance.

Feasibility of the FINDRISC questionnaire to identify individuals with impaired glucose tolerance in Swedish primary care. A cross-sectional population-based study

AIM

To evaluate the performance of the FINDRISC questionnaire as a tool to recruit individuals with impaired glucose tolerance for lifestyle intervention programmes.

METHODS

A cross-sectional population-based study in primary Health Care Centres in a middle-sized Swedish town. All 9734 individuals, aged 35-75 years, living within a defined area, were invited by mail to fill in and return the FINDRISC questionnaire. Participants with a risk score ≥ 15 (n = 525) were invited to perform an oral glucose tolerance test while those with known diabetes were excluded.

RESULTS

In total, 5452 questionnaires (58%) were returned and revealed a mean risk-score of 8.5 ± 4.5 (mean ± SD). We found that 525 participants had a risk-score ≥ 15 and 302 (58%) were further examined with an oral glucose tolerance testing (OGTT). Among them we detected 11% with previously undiagnosed Type 2 diabetes, 16% with impaired glucose tolerance and 29% with impaired fasting glucose. A FINDRISC score ≥ 15 was associated with a positive predictive value of 55% for impaired glucose metabolism (impaired fasting glucose + impaired glucose tolerance + Type 2 diabetes) and of 16% for impaired glucose tolerance, respectively. The positive predictive value for impaired glucose tolerance did not increase to more than 17% when choosing the cut-point 17, while there was a significant increase in the positive predictive value for impaired glucose metabolism (70%).

CONCLUSIONS

The FINDRISC questionnaire is a useful instrument for identification of individuals with impaired glucose metabolism but seems less effective for detection of individuals with impaired glucose tolerance. Strategies to find individuals with impaired glucose tolerance for implementation of lifestyle changes in primary care should therefore be developed further.

Atropine improves insulin sensitivity in both lean and abdominally obese subjects

BACKGROUND

Dysregulated autonomic nerve activity may contribute to the development of type 2 diabetes. The aim of this study was to assess the effects of an anticholinergic agent, atropine, and a cholinergic agent, physostigmine, on insulin sensitivity in lean and abdominally obese subjects.

SUBJECTS AND METHODS

In a single-blinded three-way crossover study, six lean and six abdominally obese nondiabetic subjects [three males and three females in each group; age, 43.8 ± 14.8 vs. 46.8 ± 4.8 yr (mean ± sd); body mass index, 22.6 ± 1.7 vs. 28.8 ± 1.3 kg/m(2); and waist circumference, 85 ± 2 vs. 99 ± 6 cm, respectively] were given iv infusions with atropine (15 μg/kg bolus, 4 μg/kg · h infusion), physostigmine (0.12 μg/kg · min) or saline (0.9% NaCl) in a randomized treatment order. Infusions were started 30 min before and continued throughout a 120-min euglycemic (5.6 mm) hyperinsulinemic (40 mU/m(2) · min) clamp.

RESULTS

Insulin sensitivity (M-value, i.e. glucose infusion rate divided by lean body mass) during the last 60 min of the clamp was higher during infusion with atropine than saline (9.2 ± 1.0 vs. 7.6 ± 1.0 mg/kg lean body mass · min, mean ± sem; P = 0.015) in all subjects. Physostigmine did not differ significantly from saline (8.2 ± 1.0). M-values were significantly higher in lean vs. obese [atropine, 11.6 ± 1.4 vs. 7.6 ± 1.3; physostigmine, 10.8 ± 1.3 vs. 6.3 ± 1.3; and saline, 9.1 ± 1.4 vs. 6.4 ± 1.3, respectively (all P < 0.05)], but the incremental effect of atropine vs. saline did not differ consistently between groups.

CONCLUSION

Insulin sensitivity was higher during a short-term atropine infusion compared with saline in both lean and abdominally obese subjects. This insulin-sensitizing effect of cholinergic blockade is unexpected, and the underlying mechanisms should be further investigated.

Impaired delivery of insulin to adipose tissue and skeletal muscle in obese women with postprandial hyperglycemia

CONTEXT

An impaired transfer of insulin from the circulation to the interstitial fluid has been suggested to contribute to insulin resistance.

OBJECTIVE

The objective of the study was to address whether the delivery of insulin from the circulation to adipose tissue and skeletal muscle is impaired in obese women with postprandial hyperglycemia compared with lean healthy controls.

DESIGN, SETTING, AND PARTICIPANTS

Seven obese nondiabetic women with postprandial hyperglycemia and nine lean healthy women were recruited. The interstitial insulin concentration in adipose tissue and muscle tissue was measured by the microdialysis technique during an oral glucose tolerance test (75 g). In parallel, arterial insulin levels were measured. We used ¹³³Xe clearance and plethysmography to monitor blood flow. Subcutaneous needle biopsies were taken to obtain fat cell size.

RESULTS

After oral glucose ingestion, mean arterial insulin levels were higher in obese women than in the lean group. However, interstitial insulin levels in sc adipose tissue and forearm muscle were similar in both groups. Accordingly, the proportion of circulating insulin being transported across the vascular endothelium to the interstitial fluid in adipose tissue and in muscle tissue was significantly lower in the obese compared with the lean group.

CONCLUSIONS

Obese subjects with postprandial hyperglycemia need higher circulating insulin levels than lean controls to attain similar interstitial insulin levels in adipose tissue and skeletal muscle, indicating an impaired transfer of insulin across the endothelium.

Hydrochlorothiazide compared to candesartan treatment increases adipose tissue gene expression and circulating levels of serum amyloid A in hypertensive patients

Treatment of hypertension with angiotensin receptor blockers has been shown to reduce the risk of developing type 2 diabetes in comparison to thiazide diuretics and beta adrenergic blockers. Therefore, we wanted to study the effect of antihypertensive drugs on adipose tissue with respect to insulin resistance. In the MEDICA (MEchanisms for the DIabetes preventing effects of CAndesartan) study, 22 hypertensive, nondiabetic patients with abdominal obesity (10 men, 12 women) were randomized into 12-week treatment periods with candesartan, hydrochlorothiazide, and placebo according to a 3-way cross-over design. Subcutaneous adipose tissue biopsies were taken after 8 weeks treatment to analyze gene expression, glucose uptake capacity, insulin-signaling, and adipocyte size. Adipose tissue gene expression of serum amyloid A (SAA) was higher after hydrochlorothiazide treatment compared to candesartan (p=0.036), and this was in accordance with our previous finding on circulating SAA levels. Serum levels of E selectin were increased after hydrochlorothiazide compared to candesartan treatment (p=0.002) and lower after candesartan compared to placebo (p=0.002). In adipocytes, there were no significant differences between the treatments with respect to cell size, glucose uptake capacity, or insulin-signaling. In comparison to candesartan, hydrochlorothiazide raised the adipose tissue gene expression of SAA and the serum level of SAA as well as E selectin in hypertensive patients. Less adipose and systemic inflammation may be one explanation why candesartan is favorable in comparison to thiazide diuretics with respect to development of insulin resistance and type 2 diabetes.

Glucose tolerance, insulin sensitivity and insulin release in European non-diabetic carriers of a polymorphism upstream of CDKN2A and CDKN2B

AIMS/HYPOTHESIS

The aim of this study was to investigate the association of the rs10811661 polymorphism near the CDKN2B/CDKN2A genes with glucose tolerance, insulin sensitivity and insulin release in three samples of white people with European ancestry.

METHODS

Sample 1 comprised 845 non-diabetic offspring of type 2 diabetes patients recruited in five European centres participating in the EUGENE2 study. Samples 2 and 3 comprised, respectively, 864 and 524 Italian non-diabetic participants. All individuals underwent an OGTT. Screening for the rs10811661 polymorphism was performed using a TaqMan allelic discrimination assay.

RESULTS

The rs10811661 polymorphism did not show a significant association with age, BMI and insulin sensitivity. Participants carrying the TT genotype showed a significant reduction in insulin release, measured by an OGTT-derived index, compared with carriers of the C allele, in the three samples. When these results were pooled with those of three published studies, and meta-analysed with a random-effects model, the T allele was significantly associated with reduced insulin secretion (-35.09 [95% CI 14.68-55.52], p = 0.0008 for CC+CT vs TT; and -29.45 [95% CI 9.51-49.38], p = 0.0038, for the additive model). In addition, in our three samples, participants carrying the TT genotype exhibited an increased risk for impaired glucose tolerance (IGT) compared with carriers of the C allele (OR 1.55 [95% CI 1.20-1.95] for the meta-analysis of the three samples).

CONCLUSIONS/INTERPRETATION

Our data, together with the meta-analysis of previously published studies, show that the rs10811661 polymorphism is associated with impaired insulin release and IGT, suggesting that this variant may contribute to type 2 diabetes by affecting beta cell function.

Tadalafil increases muscle capillary recruitment and forearm glucose uptake in women with type 2 diabetes

AIMS/HYPOTHESIS

Recent evidence suggests that reduced synthesis of nitric oxide in endothelial cells, i.e. endothelial dysfunction, contributes to the impaired action of insulin in the vasculature of patients with type 2 diabetes. We investigated whether selective inhibition of phosphodiesterase-5 by tadalafil has beneficial effects on peripheral microcirculation and glucose uptake in these patients.

METHODS

We enrolled seven postmenopausal women with type 2 diabetes and ten age-matched healthy women as controls in a placebo-controlled study to evaluate the acute metabolic effects of tadalafil. We performed microdialysis and blood flow measurements in muscle, and sampled arterial and deep venous blood before and after a single dose of tadalafil 20 mg or placebo. Circulating glucose and insulin levels, muscle capillary recruitment as reflected by permeability surface area for glucose (PS(glu)) and forearm glucose uptake were measured.

RESULTS

In women with type 2 diabetes, but not in the control group, tadalafil induced increases in the incremental AUC for PS(glu) (tadalafil vs placebo 41 +/- 11 vs 4 +/- 2 ml [100 g](-1) min(-1), p < 0.05) and forearm glucose uptake (46 +/- 9 vs 8 +/- 4 micromol [100 g](-1) min(-1), p < 0.05). The variable that best predicted forearm glucose uptake was PS(glu), which explained 70% of its variance. However, fasting glucose and insulin concentrations were similar following treatment with placebo or tadalafil in the two groups.

CONCLUSIONS/INTERPRETATION

This study suggests that tadalafil evokes positive metabolic effects in insulin-resistant women with type 2 diabetes.

Repeated measurements of 11β-HSD-1 activity in subcutaneous adipose tissue from lean, abdominally obese, and type 2 diabetes subjects--no change following a mixed meal

The aim of this study was to measure 11β-HSD-1 activity in subcutaneous adipose tissue by an ex vivo method in three subgroups; lean, obese, and type 2 diabetes subjects, both in the fasting state and after a mixed meal and to determine the variability and reproducibility of this method. Eighteen subjects were investigated; 6 lean, 6 abdominally obese, and 6 type 2 diabetes subjects (BMI 22 ± 1, 30 ± 3 and 31 ± 3 kg/m², respectively). Needle biopsies were taken repeatedly and an index of 11β-HSD-1 activity was measured as percent conversion of (3)H-cortisone to (3)H-cortisol/100 mg tissue. For two separate biopsies taken in the fasting state on the same day, the within subjects CV was 16% and the between CV was 36% for 11β-HSD-1 activity for all subjects. For two biopsies taken in the fasting state at two different days, the total within subjects CV was 38% and the between subjects CV was 46%. Lean subjects had lower 11β-HSD-1 activity (4.8 ± 1.5% conversion of ³H-cortisone to ³H-cortisol/100 mg tissue) than both obese (14.4 ± 1.6% conversion, p<0.01) and type 2 diabetes subjects (11.7 ± 1.9% conversion, p<0.05) in the fasting state. There was no effect of a meal on 11β-HSD-1 activity in any of the three groups. The conclusions from this study are: 1) the variation coefficient for the ex vivo adipose tissue 11β-HSD-1 activity method was ∼25% for repeat measures within subjects; 2) food intake had no major impact on enzyme activity; and 3) 11β-HSD-1 activity in subcutaneous adipose tissue was significantly increased in obese subjects with or without T2DM compared to lean subjects without diabetes.

The common SLC30A8 Arg325Trp variant is associated with reduced first-phase insulin release in 846 non-diabetic offspring of type 2 diabetes patients--the EUGENE2 study

AIMS/HYPOTHESIS

A recent genome-wide association study identified the SLC30A8 rs13266634 polymorphism encoding an Arg325Trp polymorphism in the zinc transporter protein member 8 (ZnT-8) to be associated with type 2 diabetes. Here, we investigate whether the polymorphism is related to altered insulin release in response to intravenous and oral glucose loads in non-diabetic offspring of type 2 diabetic patients.

METHODS

We genotyped SLC30A8 rs13266634 in 846 non-diabetic offspring of type 2 diabetic patients from five different white populations: Danish (n = 271), Finnish (n = 217), German (n = 149), Italian (n = 109) and Swedish (n = 100). Participants were subjected to both IVGTTs and OGTTs, and measurements of insulin sensitivity.

RESULTS

Homozygous carriers of the major type 2 diabetes C risk-allele showed a 19% decrease in first-phase insulin release (0-10 min) measured during the IVGTT (CC 3,624 +/- 3,197; CT 3,763 +/- 2,674; TT 4,478 +/- 3,032 pmol l(-1) min(-1), mean +/- SD; p = 0.007). We found no significant genotype effect on insulin release measured during the OGTT or on estimates of insulin sensitivity.

CONCLUSIONS/INTERPRETATION

Of European non-diabetic offspring of type 2 diabetes patients, 46% are homozygous carriers of the Arg325Trp polymorphism in ZnT-8, which is known to associate with type 2 diabetes. These diabetes-prone offspring are characterised by a 19% decrease in first-phase insulin release following an intravenous glucose load, suggesting a role for this variant in the pathogenesis of pancreatic beta cell dysfunction.

Insulin sensitivity, insulin release and glucagon-like peptide-1 levels in persons with impaired fasting glucose and/or impaired glucose tolerance in the EUGENE2 study

AIMS/HYPOTHESIS

We examined the phenotype of individuals with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) with regard to insulin release and insulin resistance.

METHODS

Non-diabetic offspring (n=874; mean age 40+/-10.4 years; BMI 26.6+/-4.9 kg/m(2)) of type 2 diabetic patients from five different European Centres (Denmark, Finland, Germany, Italy and Sweden) were examined with regard to insulin sensitivity (euglycaemic clamps), insulin release (IVGTT) and glucose tolerance (OGTT). The levels of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) were measured during the OGTT in 278 individuals.

RESULTS

Normal glucose tolerance was found in 634 participants, while 110 had isolated IFG, 86 had isolated IGT and 44 had both IFG and IGT, i.e. about 28% had a form of reduced glucose tolerance. Participants with isolated IFG had lower glucose-corrected first-phase (0-10 min) and higher second-phase insulin release (10-60 min) during the IVGTT, while insulin sensitivity was reduced in all groups with abnormal glucose tolerance. Similarly, GLP-1 but not GIP levels were reduced in individuals with abnormal glucose tolerance.

CONCLUSIONS/INTERPRETATION

The primary mechanism leading to hyperglycaemia in participants with isolated IFG is likely to be impaired basal and first-phase insulin secretion, whereas in isolated IGT the primary mechanism leading to postglucose load hyperglycaemia is insulin resistance. Reduced GLP-1 levels were seen in all groups with abnormal glucose tolerance and were unrelated to the insulin release pattern during an IVGTT.

Insulin differentially modulates the peripheral endocannabinoid system in human subcutaneous abdominal adipose tissue from lean and obese individuals

Human obesity has been associated with a dysregulation of the peripheral and adipose tissue (AT) endocannabinoid system (ES). The aim of this study was to elucidate the acute in vivo effects of insulin on gene expression of the cannabinoid type 1 (CB-1) and type 2 (CB-2) receptors, as well as of the fatty acid amide hydrolase (FAAH) in the sc abdominal adipose tissue (SCAAT). Nine lean (L) and 9 obese (OB), but otherwise healthy males were studied in the fasting state and during a euglycemic hyperinsulinemic clamp (40 mU/m2 * min(-1)). SCAAT biopsies were obtained at baseline and after 270 min of i.v. maintained hyperinsulinemia. The basal SCAAT gene expression pattern revealed an upregulation of the FAAH in the OB (p=0.03 vs L), whereas similar CB-1 and CB-2 mRNA levels were seen. Following hyperinsulinemia, the FAAH mRNA levels significantly increased approximately 2-fold in the L (p=0.01 vs baseline) but not in the OB. In contrast, insulin failed to significantly change both the adipose CB-1 and CB-2 gene expression. Finally, the FAAH gene expression positively correlated with the fasting serum insulin concentration (r 0.66; p=0.01), whereas an inverse association with the whole-body glucose disposal (r -0.58; p<0.05) was seen. Taken together, these first time observations demonstrate that the ES-related genes in the SCAAT differentially respond to hyperinsulinemia in lean/insulin-sensitive and in obese/insulin-resistant individuals. We suggest that insulin may play a key role in the obesity-linked dysregulation of the adipose ES at the gene level.

Endothelial dysfunction in insulin resistance and type 2 diabetes

Macrovascular disease is the number one killer in type 2 diabetes patients. The cluster of risk factors in the insulin resistance syndrome (IRS) partly explains this notion. Insulin action in muscle, liver or adipose tissue has been thoroughly described in the literature, whilst this has been less described for the endothelium. Insulin stimulates nitric oxide (NO) production in the endothelium and reduced bioavailability of NO is usually defined as endothelial dysfunction. This impairment might be related to defective insulin signalling in the endothelial cell. Therefore, insulin resistance mechanisms in the endothelial cell will be emphasized in this review. Imbalance between the vasodilating agent NO and the vasoconstrictor endothelin-1 (ET-1) contributes to endothelial dysfunction. Different methods and circulating markers to assess endothelial function will be outlined. Circulating markers of an activated endothelium appear long before type 2 diabetes develops suggesting a unique role of the endothelium in the pathophysiology of the disease. Hampered blood flow in nutritive capillaries due to endothelial dysfunction is coupled with decreased glucose uptake and hyperglycemia. The forearm model combined with muscle microdialysis enables us to measure interstitial glucose and an index for capillary recruitment, the permeability surface area (PS). Available data from this method suggest that capillary recruitment in response of insulin is impaired in insulin resistant human subjects.

Postprandial interstitial insulin concentrations in type 2 diabetes relatives

BACKGROUND

An endothelial barrier for the insulin transport from the circulation to the target tissues of insulin has previously been suggested to contribute to insulin resistance. The interstitial insulin concentration (I-insulin) and insulin kinetics following a mixed meal have, however, previously not been characterized in human adipose tissue.

SUBJECTS AND METHODS

Eight nondiabetic first-degree relatives (FDR) of type 2 diabetes patients were recruited. Their I-insulin was measured by microdialysis after a test meal with or without oral administration of the insulin secretagogue nateglinide (120 mg). In parallel, adipose tissue blood flow and lipolysis were measured by xenon-clearance and microdialysis, respectively.

RESULTS

The I-insulin increased after the test meal, and this response was more prominent on the day the subjects received the nateglinide tablet when compared with the day the subjects received the placebo tablet [I-insulin incremental area under the curve (IAUC) nateglinide 7612 +/- 3032 vs. Plac 4682 +/- 2613 pmol L(-1) min; P < 0.05, mean +/- SE]. However, the postprandial I-insulin(max)/P-insulin(max) ratio was similar on the two test days (nateglinide: 213 +/- 62 vs. 501 +/- 92 pmol L(-1), I/P-ratio: 0.38 +/- 0.06 and placebo: 159 +/- 39 vs. 410 +/- 74 pmol L(-1), I/P-ratio: 0.36 +/- 0.05). There was no difference in time of onset of insulin action in situ, or responsiveness, when comparing placebo and nateglinide.

CONCLUSIONS

Microdialysis can now be used to measure the I-insulin in human adipose tissue following a mixed meal. The data also showed that the transendothelial delivery of insulin occurs rapidly, supporting the concept that transcapillary insulin transfer is a nonsaturable process in nondiabetic first-degree relatives of type 2 diabetes patients.

No acute effect of nateglinide on postprandial lipid and lipoprotein responses in subjects at risk for type 2 diabetes

BACKGROUND

To study the acute effect of nateglinide, an insulinotropic agent, on the postprandial triglyceride and lipoprotein responses in subjects at risk for type 2 diabetes.

METHODS

Six women and 10 men, with at least one first-degree relative with type 2 diabetes were included (Age: 48 +/- 7 years, BMI: 27.5 +/- 2.8 kg m(-2), P-triglycerides: 1.3 +/- 0.4 mmol L(-1), P-cholesterol: 5.4 +/- 0.6 mmol L(-1), B-glucose: 4.6 +/- 0.3 mmol L(-1)). They each had two 8-h meal tolerance tests with either nateglinide or placebo given 10 min prior to the meals in randomized order. Lipoprotein fractions were separated by density gradient ultracentrifugation. First-phase insulin secretion was assessed by an intravenous glucose tolerance test (300 mg kg(-1) body weight) and insulin sensitivity by a hyperinsulinaemic euglycaemic clamp (40 mU m(-2) min(-1)).

RESULTS

The 1-h insulin levels during the meal tolerance test were significantly higher with nateglinide (577 +/- 81 vs 376 +/- 58 pmol L(-1), p < 0.001), as well as the response during the first two hours (IAUC: 41 243 +/- 5844 vs 29 956 +/- 4662 pmol L(-1) min, p < 0.01). Accordingly, nateglinide lowered the 8-h postprandial glucose response by around 60% compared to placebo (p < 0.001). In contrast, no significant lowering was seen in the excursion of postprandial triglycerides in total plasma or lipoprotein fractions. Consistently, the concentration of exogenous (apoB-48) and endogenous (apoB-100) lipoproteins was not reduced by nateglinide.

CONCLUSIONS

Acute administration of nateglinide reduces, as expected, the postprandial glucose concentration, but no reduction in triglyceride or lipoprotein responses are seen in subjects at risk for type 2 diabetes.

Improved insulin sensitivity and adipose tissue dysregulation after short-term treatment with pioglitazone in non-diabetic, insulin-resistant subjects

AIMS/HYPOTHESIS

We examined whether short-term treatment with a thiazolidinedione improves insulin sensitivity in non-obese but insulin-resistant subjects and whether this is associated with an improvement in dysregulated adipose tissue (reduced expression of IRS-1, GLUT4, PPARgamma co-activator 1 and markers of terminal differentiation) that we have previously documented to be associated with insulin resistance.

METHODS

Ten non-diabetic subjects, identified as having low IRS-1 and GLUT-4 protein in adipose cells as markers of insulin resistance, underwent 3 weeks of treatment with pioglitazone. The euglycaemic-hyperinsulinaemic clamp technique was used to measure insulin sensitivity before and after treatment. Serum samples were analysed for glucose, insulin, lipids, total and high-molecular-weight (HMW) adiponectin levels. Biopsies from abdominal subcutaneous adipose tissue were taken, cell size measured, mRNA and protein extracted and quantified using real-time RT-PCR and Western blot.

RESULTS

Insulin sensitivity was improved after 3 weeks treatment and circulating total as well as HMW adiponectin increased in all subjects, while no effect was seen on serum lipids. In the adipose cells, gene and protein expression of IRS-1 and PPARgamma co-activator 1 remained unchanged, while adiponectin, adipocyte P 2, uncoupling protein 2, GLUT4 and liver X receptor-alpha increased. Insulin-stimulated tyrosine phosphorylation and p-ser-PKB/Akt increased, while no significant effect of thiazolidinedione treatment was seen on the inflammatory status of the adipose tissue in these non-obese subjects.

CONCLUSIONS/INTERPRETATION

Short-term treatment with pioglitazone improved insulin sensitivity in the absence of any changes in circulating NEFA or lipid levels. Several markers of adipose cell differentiation, previously shown to be reduced in insulin resistance, were augmented, supporting the concept that insulin resistance in these individuals is associated with impaired terminal differentiation of the adipose cells.

Early alterations in the postprandial VLDL1 apoB-100 and apoB-48 metabolism in men with strong heredity for type 2 diabetes

OBJECTIVES

To study the postprandial triglyceride-rich lipoprotein (TRL) metabolism, specifically the concentrations of very low-density lipoproteins (VLDL); from intestine (apoB-48) and liver (apoB-100), in men with normal fasting triglycerides but at increased risk of developing type 2 diabetes.

DESIGN

Cross-sectional study.

SUBJECTS AND SETTINGS

Sixteen healthy men with at least two first-degree relatives with type 2 diabetes were individually matched with 16 control subjects without known diabetes heredity for: age, body mass index, and fasting triglyceride level. They underwent an 8-h meal tolerance test (919 kcal, 51 g fat) during which lipoproteins were separated by density gradient ultracentrifugation. They were characterized by euglycaemic hyperinsulinaemic clamp, peak VO2, 7-day diet registration and computed tomography.

RESULTS

The relatives were, as expected, more insulin resistant than the controls and had increased concentration of postprandial VLDL1 particles (49% higher for VLDL1 apoB-48, P = 0.04 and 21% higher for VLDL1 apoB-100, P = 0.048). The elevation was related to insulin sensitivity, but not to lifestyle and body composition. Moreover, the concentration of postprandial triglycerides in VLDL1 fraction was inversely related to low-density lipoprotein (LDL) size in both relatives (rs = -0.60, P = 0.03) and controls (rs = -0.72, P = 0.004). There were no differences in the concentration of triglycerides or apoB-48 and apoB-100 particles in the other fractions (plasma, chylomicron or VLDL2).

CONCLUSION

Increased postprandial concentration of TRLs in the VLDL1 fraction seems to be present at an early stage in the development of diabetes and probably contributes to the excess risk of future coronary events in insulin-resistant men.

Circulating adiponectin levels are reduced in nonobese but insulin-resistant first-degree relatives of type 2 diabetic patients

Adiponectin, one of the most abundant gene transcript proteins in human fat cells, has been shown to improve insulin action and is also suggested to exert antiatherogenic effects. We measured circulating adiponectin levels and risk factors for atherosclerosis in 45 healthy first-degree relatives of type 2 diabetic subjects (FDR) as well as 40 healthy control subjects (CON) without a known family history of diabetes. Insulin sensitivity (S(i)) was studied with the minimal model, and measurements of adiponectin, metabolic variables, inflammatory markers, and endothelial injury markers, as well as lipoprotein concentrations, were performed. FDR were insulin resistant (3.3 +/- 2.4 vs. 4.5 +/- 2.6 x 10(-4) x min(-1) per microU/ml [mean +/- SD], P < 0.01), and their circulating plasma adiponectin levels (6.6 +/- 1.8 vs. 8.1 +/- 3.0 microg/ml, P < 0.03) were decreased. After adjustments for age in FDR, adiponectin levels were negatively correlated with fasting proinsulin (r -0.64, P < 0.001), plasminogen activator inhibitor (PAI)-1 activity (r -0.56, P < 0.001), fasting insulin (r -0.55, P < 0.001), and acute insulin response (r -0.40, P < 0.05); they were positively related to HDL cholesterol (r 0.48, P < 0.01) and S(i) (r 0.41, P < 0.01). Furthermore, when adjusted for age, waist, and S(i), adiponectin was associated with HDL cholesterol and proinsulin, which explained 51% of the variation in adiponectin in multiple regression analyses in that group. In conclusion, circulating plasma adiponectin levels were decreased in nonobese but insulin-resistant FDR and, in addition, related to several facets of the insulin resistance syndrome (IRS). Thus, hypoadiponectinemia may be an important component of the association between cardiovascular disease and IRS.

Reduced expression of PGC-1 and insulin-signaling molecules in adipose tissue is associated with insulin resistance

Peroxisome proliferator-activated receptor gamma (PPAR gamma) co-activator 1 (PGC-1) regulates glucose metabolism and energy expenditure and, thus, potentially insulin sensitivity. We examined the expression of PGC-1, PPAR gamma, insulin receptor substrate-1 (IRS-1), glucose transporter isoform-4 (GLUT-4), and mitochondrial uncoupling protein-1 (UCP-1) in adipose tissue and skeletal muscle from non-obese, non-diabetic insulin-resistant, and insulin-sensitive individuals. PGC-1, both mRNA and protein, was expressed in human adipose tissue and the expression was significantly reduced in insulin-resistant subjects. The expression of PGC-1 correlated with the mRNA levels of IRS-1, GLUT-4, and UCP-1 in adipose tissue. Furthermore, the adipose tissue expression of PGC-1 and IRS-1 correlated with insulin action in vivo. In contrast, no differential expression of PGC-1, GLUT-4, or IRS-1 was found in the skeletal muscle of insulin-resistant vs insulin-sensitive subjects. The findings suggest that PGC-1 may be involved in the differential gene expression and regulation between adipose tissue and skeletal muscle. The combined reduction of PGC-1 and insulin signaling molecules in adipose tissue implicates adipose tissue dysfunction which, in turn, can impair the systemic insulin response in the insulin-resistant subjects.

Validation of a glucose-insulin-potassium infusion algorithm in hospitalized diabetic patients

OBJECTIVES

Validation of a novel glucose-insulin-potassium (GIK) infusion algorithm to optimize metabolic control in hospitalized diabetic patients.

SUBJECTS

We randomized 33 diabetic patients admitted to Sahlgrenska University Hospital with acute internal medicine diseases to either GIK infusion or multiple injection therapy (MIT). The GIK infusion rate and the MIT were controlled according to special algorithms. The treatment efficacy was evaluated through comparisons of capillary blood glucose eight times on day 2 of the study.

RESULTS

The GIK infusion led to significantly lower mean blood glucose when compared with MIT [10.1 (9.0-11.2) vs. 12.3 (9.3-14.4) mmol L(-1), median and interquartile range, P < 0.01]. Four episodes of hypoglycaemia without loss of consciousness were recorded in the GIK group whereas no hypoglycaemic event occurred in the MIT group. A mean of 1 (1-3) episodes of blood glucose levels above 12.0 mmol L(-1) were recorded in the GIK group compared with 3.5 (1.5-5.0) in the MIT group, P < 0.01.

CONCLUSIONS

The algorithm used for the GIK infusion gave an acceptable level of metabolic control and this insulin infusion protocol is safe enough to be used by the nursing staff on a general internal medicine ward.

Endocrine abnormalities in healthy first-degree relatives of type 2 diabetes patients--potential role of steroid hormones and leptin in the development of insulin resistance

BACKGROUND

First-degree relatives of type 2 diabetes patients are at risk of developing diabetes and they display several metabolic and hormonal perturbations. The interplay between insulin resistance, steroid hormones and circulating leptin is, however, still not fully explored in this group.

DESIGN

Thirty-three healthy first-degree relatives of type 2 diabetic patients (relatives; M/F 19/14) were compared to 33 healthy subjects without a family history of diabetes (controls) and the groups were matched for gender, age and body mass index (BMI). We performed euglycaemic hyperinsulinaemic clamps and blood was sampled for hormone analyses.

RESULTS

Relatives exhibited decreased insulin sensitivity (index of metabolic clearance rate of glucose; MCRI) but when genders were analysed separately, this difference was significant only in males (11.3 +/- 1.3 vs. 15.0 +/- 1.5 units, means +/- SEM, P = 0.030). In male relatives morning cortisol and testosterone levels were lower, whereas leptin was higher than in male controls (P = 0.018, 0.008 and 0.063, respectively). In male relatives plasma testosterone levels were significantly associated with insulin sensitivity (r = 0.48, P = 0.040). Circulating leptin levels were inversely correlated with insulin sensitivity in all subject groups (r-values -0.49 to -0.66; P < 0.05, except in female control subjects P = 0.063). These associations were present also when age and BMI or waist:hip ratio were included in stepwise multiple regression analyses.

CONCLUSION

Male subjects genetically predisposed for type 2 diabetes display several endocrine abnormalities including leptin, cortisol and testosterone levels. Dysregulation of these hormones may be important in the development of insulin resistance and type 2 diabetes.

Determination of Lewis FUT3 gene mutations by PCR using sequence-specific primers enables efficient genotyping of clinical samples

We have developed a polymerase chain reaction method using sequence-specific primers (PCR-SSP) for rapid and correct genotyping of the common Lewis (FUT3) gene mutations 59T>G, 202T>C, 314C>T, 508G>A, and 1067T>A. The PCR-SSP method was validated on 20 healthy blood donors and 16 non-insulin-dependent diabetic patients. All individuals were in parallel genotyped by our established polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. The FUT3 genotypes, determined with the PCR-SSP method, were in complete accordance with the results of the PCR-RFLP reference method. The PCR-SSP method could also be adapted to assign the presence of a specific mutation to the respective FUT3 alleles. We found the method to be reliable, rapid and cheap with no requirements for restriction enzyme processing.

Increased lactate release per fat cell in normoglycemic first-degree relatives of individuals with type 2 diabetes

The aim of this study was to examine subcutaneous lactate production in the relatives of individuals with type 2 diabetes. Therefore, we recruited seven healthy first-degree relatives of type 2 diabetic patients and seven pairwise, matched, healthy control subjects without any heredity for diabetes. All subjects were studied with a euglycemic insulin clamp at approximately 600 pmol/l, abdominal subcutaneous microdialysis, and (133)Xe clearance. Furthermore, a subcutaneous needle biopsy was performed to determine fat cell size. In the fasting state, interstitial lactate was 40% higher in relatives than in control subjects (P = 0.043), but net lactate production was similar in both groups. However, during the insulin clamp, interstitial lactate (2.50 +/- 0.29 vs. 1.98 +/- 0.26 mmol/l, P = 0.018), interstitial-arterial lactate concentration difference (1.08 +/- 0.30 vs. 0.53 +/- 0.24 mmol/l, P = 0.028), and net lactate release per fat cell (10.9 +/- 3.7 vs. 2.8 +/- 1.3 fmol. cell(-1). min(-1), P = 0.018) were increased in the relatives. We conclude that first-degree relatives of type 2 diabetic patients may have an enhanced net lactate release per fat cell in abdominal subcutaneous tissue. This could suggest a pathological regulation in adipose tissue that is of importance for the metabolic defects known in type 2 diabetic relatives.

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.