Metabolic profiling of galectin-1 and galectin-3: a cross-sectional, multi-omics, association study.

OBJECTIVES: Experimental studies indicate a role for galectin-1 and galectin-3 in metabolic disease, but clinical evidence from larger populations is limited. METHODS: We measured circulating levels of galectin-1 and galectin-3 in the Prospective investigation of Obesity, Energy and Metabolism (POEM) study, participants (n = 502, all aged 50 years) and characterized the individual association profiles with metabolic markers, including clinical measures, metabolomics, adipose tissue distribution (Imiomics) and proteomics. RESULTS: Galectin-1 and galectin-3 were associated with fatty acids, lipoproteins and triglycerides including lipid measurements in the metabolomics analysis adjusted for body mass index (BMI). Galectin-1 was associated with several measurements of adiposity, insulin secretion and insulin sensitivity, while galectin-3 was associated with triglyceride-glucose index (TyG) and fasting insulin levels. Both galectins were associated with inflammatory pathways and fatty acid binding protein (FABP)4 and -5-regulated triglyceride metabolic pathways. Galectin-1 was also associated with several proteins related to adipose tissue differentiation. CONCLUSIONS: The association profiles for galectin-1 and galectin-3 indicate overlapping metabolic effects in humans, while the distinctly different associations seen with fat mass, fat distribution, and adipose tissue differentiation markers may suggest a functional role of galectin-1 in obesity.

Feasibility of high-dose tadalafil and effects on insulin resistance in well-controlled patients with type 2 diabetes (MAKROTAD): a single-centre, double-blind, randomised, placebo-controlled, cross-over phase 2 trial.

Background: Phosphodiesterase-5 inhibitors exert positive vascular and metabolic effects in type 2 diabetes (T2D), but the effect on insulin resistance in T2D is unclear. Methods: This randomised, double blind, placebo-controlled, two-period crossover trial was conducted at Sahlgrenska University Hospital (Gothenburg, Sweden). Men without apparent erectile dysfunction (age 40-70 years) and women (age 55-70 years, post-menopause) diagnosed with T2D between 3 months and 10 years, haemoglobin A1c (HbA1c) < 60 mmol/mol and a body mass index (BMI) 27-40 kg/m2 were enrolled. Participants were randomly assigned to one period of oral tadalafil 20 mg once a day and one period of placebo for 6 weeks, separated by an 8-week wash-out period. Placebo and tadalafil tablets were made visually indistinguishable and delivered randomized in two separate boxes for each participant. Both treatment periods ended with a glucose clamp, and measurements of body composition and metabolic markers in blood, subcutaneous and muscular interstitial fluid. The primary aim was to assess difference in whole-body insulin resistance after 6-weeks of treatment, determined after completion of the two study arms, and secondary aims were to study effects of tadalafil on pathophysiology of T2D as well as tolerability of high-dose tadalafil in T2D. Primary analysis was performed in participants with full analysis set (FAS) and safety analysis in all participants who received at least one dose of study medication. This trial is registered with ClinicalTrials.gov (NCT02601989), and EudraCT (2015-000573). Findings: Between January 22nd, 2016, and January 31st, 2019, 23 participants with T2D were enrolled, of whom 18 were included in the full analysis set. The effect of tadalafil on insulin resistance was neutral compared with placebo. However, tadalafil decreased glycaemia measured as HbA1c (mean difference -2.50 mmol/mol, 95% confidence interval (CI), -4.20; -0.78, p = 0.005), and, further, we observed amelioration of endothelial function and markers of liver steatosis and glycolysis, whereas no statistically significant differences of other clinical phenotyping were shown. Muscle pain, dyspepsia, and headache were more frequent in participants on high-dose tadalafil compared with placebo (p < 0.05) but no difference between treatments appeared for serious adverse events. Interpretation: High-dose tadalafil does not decrease whole-body insulin resistance, but increases microcirculation, induces positive effects in the liver and in intermediate metabolites, in parallel with an improved metabolic control measured as HbA1c. High-dose tadalafil is moderately well tolerated, warranting larger trials to define the optimal treatment regimen in T2D. Funding: The Swedish Research Council, Swedish Diabetes Foundation, Novo Nordisk Foundation, the Swedish state under the agreement between the Swedish government and the county councils, the ALF-agreement, Sahlgrenska University Hospital funds, Gothenburg Society of Medicine, Eli Lilly & Company, USA, and Eli Lilly & Company, Sweden AB.

The role of circulating galectin-1 in type 2 diabetes and chronic kidney disease: evidence from cross-sectional, longitudinal and Mendelian randomisation analyses.

AIMS/HYPOTHESIS: Galectin-1 modulates inflammation and angiogenesis, and cross-sectional studies indicate that galectin-1 may be a uniting factor between obesity, type 2 diabetes and kidney function. We examined whether circulating galectin-1 can predict incidence of chronic kidney disease (CKD) and type 2 diabetes in a middle-aged population, and if Mendelian randomisation (MR) can provide evidence for causal direction of effects. METHODS: Participants (n = 4022; 58.6% women) in the Malmö Diet and Cancer Study-Cardiovascular Cohort enrolled between 1991 and 1994 (mean age 57.6 years) were examined. eGFR was calculated at baseline and after a mean follow-up of 16.6 ± 1.5 years. Diabetes status was ascertained through registry linkage (mean follow-up of 18.4 ± 6.1 years). The associations of baseline galectin-1 with incident CKD and type 2 diabetes were assessed with Cox regression, adjusting for established risk factors. In addition, a genome-wide association study on galectin-1 was performed to identify genetic instruments for two-sample MR analyses utilising the genetic associations obtained from the Chronic Kidney Disease Genetics (CKDGen) Consortium (41,395 cases and 439,303 controls) and the DIAbetes Genetics Replication And Meta-analysis (DIAGRAM) consortium (74,124 cases and 824,006 controls). One genome-wide significant locus in the galectin-1 gene region was identified (sentinel SNP rs7285699; p = 2.4 × 10-11). The association between galectin-1 and eGFR was also examined in individuals with newly diagnosed diabetes from the All New Diabetics In Scania (ANDIS) cohort. RESULTS: Galectin-1 was strongly associated with lower eGFR at baseline (p = 2.3 × 10-89) but not with incident CKD. However, galectin-1 was associated with increased risk of type 2 diabetes (per SD increase, HR 1.12; 95% CI 1.02, 1.24). Two-sample MR analyses could not ascertain a causal effect of galectin-1 on CKD (OR 0.92; 95% CI 0.82, 1.02) or type 2 diabetes (OR 1.05; 95% CI 0.98, 1.14) in a general population. However, in individuals with type 2 diabetes from ANDIS who belonged to the severe insulin-resistant diabetes subgroup and were at high risk of diabetic nephropathy, genetically elevated galectin-1 was significantly associated with higher eGFR (p = 5.7 × 10-3). CONCLUSIONS/INTERPRETATION: Galectin-1 is strongly associated with lower kidney function in cross-sectional analyses, and two-sample MR analyses suggest a causal protective effect on kidney function among individuals with type 2 diabetes at high risk of diabetic nephropathy. Future studies are needed to explore the mechanisms by which galectin-1 affects kidney function and whether it could be a useful target among individuals with type 2 diabetes for renal improvement.

Hyperinsulinemia and insulin resistance in the obese may develop as part of a homeostatic response to elevated free fatty acids: A mechanistic case-control and a population-based cohort study.

BACKGROUND: It is commonly accepted that in obesity free fatty acids (FFA) cause insulin resistance and hyperglycemia, which drives hyperinsulinemia. However, hyperinsulinemia is observed in subjects with normoglycaemia and thus the paradigm above should be reevaluated. METHODS: We describe two studies: MD-Lipolysis, a case control study investigating the mechanisms of obesity-driven insulin resistance by a systemic metabolic analysis, measurements of adipose tissue lipolysis by microdialysis, and adipose tissue genomics; and POEM, a cohort study used for validating differences in circulating metabolites in relation to adiposity and insulin resistance observed in the MD-Lipolysis study. FINDINGS: In insulin-resistant obese with normal glycaemia from the MD-Lipolysis study, hyperinsulinemia was associated with elevated FFA. Lipolysis, assessed by glycerol release per adipose tissue mass or adipocyte surface, was similar between obese and lean individuals. Adipose tissue from obese subjects showed reduced expression of genes mediating catecholamine-driven lipolysis, lipid storage, and increased expression of genes driving hyperplastic growth. In the POEM study, FFA levels were specifically elevated in obese-overweight subjects with normal fasting glucose and high fasting levels of insulin and C-peptide. INTERPRETATION: In obese subjects with normal glycaemia elevated circulating levels of FFA at fasting are the major metabolic derangement candidate driving fasting hyperinsulinemia. Elevated FFA in obese with normal glycaemia were better explained by increased fat mass rather than by adipose tissue insulin resistance. These results support the idea that hyperinsulinemia and insulin resistance may develop as part of a homeostatic adaptive response to increased adiposity and FFA. FUNDING: Swedish-Research-Council (2016-02660); Diabetesfonden (DIA2017-250; DIA2018-384; DIA2020-564); Novo-Nordisk-Foundation (NNF17OC0027458; NNF19OC0057174); Cancerfonden (CAN2017/472; 200840PjF); Swedish-ALF-agreement (2018-74560).

Galectin-1 is inversely associated with type 2 diabetes independently of obesity - A SCAPIS pilot study.

OBJECTIVES: Galectin-1 is a recently discovered adipokine that increases with obesity and increased energy intake in adipose tissue. Our aim was to assess whether serum galectin-1 is associated with type 2 diabetes (T2D) and other parameters of the metabolic syndrome independently of body mass index (BMI) in a cohort from the general population. METHODS: In this cross-sectional population-based cohort study from the western part of Sweden, we investigated associations between serum galectin-1, clinical characteristics and inflammatory markers in 989 women and men aged 50-65 years [part of the Swedish CArdioPulmonary bioImage Study (SCAPIS) pilot cohort]. RESULTS: We showed in linear models that serum galectin-1 was independently and: (1) inversely associated with T2D (p < 0.05) and glucose (p < 0.05); and (2) positively associated with age (p < 0.01), sex (p < 0.01), BMI (p < 0.01), insulin (p < 0.01) and C-reactive protein (p < 0.01). Furthermore, galectin-1 demonstrated univariate correlations with triglycerides (r = 0.20, p < 0.01), homeostasis model assessment for insulin resistance (r = 0.24, p < 0.01), tumor necrosis factor-α (r = 0.24, p < 0.01), interleukin-6 (IL-6; r = 0.20, p < 0.01) and HbA1c (r = 0.14, p < 0.01). CONCLUSION: In a cross-sectional study of a middle-aged population, we showed that serum galectin-1 is: (1) inversely associated with T2D independently of BMI; and (2) independently associated with other markers of the metabolic syndrome These results warrant prospective and functional studies on the role of galectin-1 in T2D.

Microdialysis and proteomics of subcutaneous interstitial fluid reveals increased galectin-1 in type 2 diabetes patients.

OBJECTIVE: To identify a potential therapeutic target for type 2 diabetes by comparing the subcutaneous interstitial fluid from type 2 diabetes patients and healthy men. METHODS: Proteomics was performed on the interstitial fluid of subcutaneous adipose tissue obtained by microdialysis from 7 type 2 diabetes patients and 8 healthy participants. 851 proteins were detected, of which 36 (including galectin-1) showed significantly altered expression in type 2 diabetes. We also measured galectin-1 expression in: (1) adipocytes isolated from adipose tissue biopsies from these participants; (2) subcutaneous adipose tissue of 24 obese participants before, during and after 16weeks on a very low calorie diet (VLCD); and (3) adipocytes isolated from 6 healthy young participants after 4weeks on a diet and lifestyle intervention to promote weight gain. We also determined the effect of galectin-1 on glucose uptake in human adipose tissue. RESULTS: Galectin-1 protein levels were elevated in subcutaneous dialysates from type 2 diabetes compared with healthy controls (p<0.05). In agreement, galectin-1 mRNA expression was increased in adipocytes from the type 2 diabetes patients (p<0.05). Furthermore, galectin-1 mRNA expression was decreased in adipose tissue after VLCD (p<0.05) and increased by overfeeding (p<0.05). Co-incubation of isolated human adipocytes with galectin-1 reduced glucose uptake (p<0.05) but this was independent of the insulin signal. CONCLUSION: Proteomics of the interstitial fluid in subcutaneous adipose tissue in vivo identified a novel adipokine, galectin-1, with a potential role in the pathophysiology of type 2 diabetes.

The selective phosphodiesterase-5 inhibitor tadalafil induces microvascular and metabolic effects in type 2 diabetic postmenopausal females.

OBJECTIVE: The objective of the study was to explore the acute in vivo effects of the selective phosphodiesterase-5 inhibitor tadalafil on local microcirculation and regional metabolism in skeletal muscle and adipose tissue (AT). DESIGN, SETTING, AND PARTICIPANTS: We studied eight postmenopausal female patients with type 2 diabetes (T2D) and eight nondiabetic controls (Ctrl) in the postabsorptive state and 180 min after the administration of tadalafil 10 mg. Intramuscular and sc microdialysis were combined with measurements of forearm (FBF) and AT blood flow as well as with arterial and deep venous blood sampling. Muscle capillary recruitment, as ascertained by the permeability surface area product for glucose (PS(glu)), forearm glucose uptake (FGU), interstitial lactate, and glycerol concentrations, was measured. RESULTS: When compared with Ctrl, T2D patients exhibited lower (P = 0.01) PS(glu) but similar FGU and FBF. After tadalafil, PS(glu) (P = 0.01) and muscle interstitial-arterial (I-A) lactate concentration gradient (P < 0.01) increased significantly in both groups, whereas FBF, FGU, and I-A glycerol remained unchanged. In AT, tadalafil did not significantly affect local blood flow, whereas the sc interstitial (I) lactate and I-A lactate concentrations increased (P < 0.01), and the I-A glycerol decreased in both groups. Finally, in multivariate analysis the PS(glu) was a strong and independent predictor of muscle glucose disposal (ß: 0.737 and 0.963, P < 0.05, in Ctrl and T2D, respectively). CONCLUSIONS: Tadalafil emerges as an acutely acting modulator of microvascular recruitment and glucose metabolism in skeletal muscle and adipose tissue. We suggest that selective phosphodiesterase-5 blockade may provide a path forward to new therapeutics in the setting of insulin resistance.

Effects of Intrabrachial metacholine infusion on muscle capillary recruitment and forearm glucose uptake during physiological hyperinsulinemia in obese, insulin-resistant individuals.

CONTEXT: Impairment of insulin-mediated capillary recruitment in skeletal muscle contributes to a hampered glucose uptake in obesity. OBJECTIVE: The objective of this study was to evaluate whether metacholine (MCh), a nitric oxide vasodilator, potentiates muscle capillary recruitment and forearm glucose uptake (FGU) during physiological hyperinsulinemia. DESIGN: The double-forearm technique [i.e. infused vs. control (Ctrl) forearm] was combined with im microdialysis during an oral glucose tolerance test in 15 nondiabetic, obese subjects divided into a group of insulin-resistant (IR) (n = 7) and insulin-sensitive (n = 8) individuals. RESULTS: After the oral glucose tolerance test, forearm blood flow in the Ctrl forearm was unchanged, whereas it increased about 3-fold (P < 0.0001 vs. baseline) in response to MCh. Capillary permeability surface area product for glucose (PS(glu)) (capillary recruitment), FGU, and interstitial insulin concentrations increased significantly over time (P < 0.001) in both forearms. Compared with insulin-sensitive, the IR subjects exhibited lower PS(glu) (P < 0.001) and FGU (P < 0.01) in the Ctrl arm, whereas this difference was insignificant in the MCh arm despite the blunted forearm blood flow increase. Moreover, in IR individuals MCh significantly (P < 0.05) ameliorated the delayed onset of insulin action, i.e. the FGU response to hyperinsulinemia. Finally, we found PS(glu) to be a strong and independent predictor of FGU response (adjusted R(2) 0.72; P < 0.0001). CONCLUSIONS: MCh-induced vasodilation may improve the microvascular and metabolic responses to physiological hyperinsulinemia in obese, IR individuals. Further studies are required to unravel whether stimulation of nitric oxide production in skeletal muscle may represent an attractive therapeutic approach to bypassing cellular resistance to glucose disposal.

Cyclic adenosine monophosphate-phosphodiesterase inhibitors reduce skeletal muscle protein catabolism in septic rats.

We have previously shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cyclic adenosine monophosphate (cAMP) cascade in normal rats. In the present work, we investigated in vivo and in vitro effects of cAMP-phosphodiesterase inhibitors on protein metabolism in skeletal muscle from rats submitted to a model of acute sepsis. The in vivo muscle protein metabolism was evaluated indirectly by measurements of the tyrosine interstitial concentration using microdialysis. Muscle blood flow (MBF) was monitored by ethanol perfusion technique. Sepsis was induced by cecal ligation and puncture and resulted in lactate acidosis, hypotension, and reduction in MBF (-30%; P < 0.05). Three-hour septic rats showed an increase in muscle interstitial tyrosine concentration (approximately 150%), in arterial plasma tyrosine levels (approximately 50%), and in interstitial-arterial tyrosine concentration difference (approximately 200%; P < 0.05). Pentoxifylline (50 mg/kg of body weight, i.v.) infusion during 1 h after cecal ligation and puncture prevented the tumor necrosis factor alpha increase and significantly reduced by 50% (P < 0.05) the interstitial-arterial tyrosine difference concentration. In situ perfusion with isobutylmethylxanthine (IBMX; 10(-3) M) reduced by 40% (P < 0.05) the muscle interstitial tyrosine in both sham-operated and septic rats. Neither pentoxifylline nor IBMX altered MBF. The addition of IBMX (10(-3) M) to the incubation medium increased (P < 0.05) muscle cAMP levels and reduced proteolysis in both groups. The in vitro addition of H89, a protein kinase A inhibitor, completely blocked the antiproteolytic effect of IBMX. The data show that activation of cAMP-dependent pathways and protein kinase A reduces muscle protein catabolism during basal and septic state.

Decreased muscle capillary permeability surface area in type 2 diabetic subjects.

Capillary recruitment in muscles, induced by insulin, has been proposed to be impaired in insulin-resistant states. To elucidate the mechanisms regulating capillary transport of insulin and glucose in type 2 diabetes, we directly calculated the permeability-surface area product (PS) for glucose and insulin in muscle. Intramuscular microdialysis in combination with the forearm model and blood flow measurements was performed in type 2 diabetic male subjects and age- and weight-matched controls during a euglycemic-hyperinsulinemic clamp. During steady-state hyperinsulinemia, arterial plasma glucose was 5.8 +/- 0.1 and 5.9 +/- 0.1 mmol/liter [not significant (NS)] in the obese and type 2 diabetic subjects, respectively. Venous glucose was significantly lower in the obese group compared with the type 2 diabetic subjects, 4.3 +/- 02 vs. 4.9 +/- 0.2 mmol/liter (P < 0.05). Arterial insulin was 1494 +/- 90 and 1458 +/- 132 pmol/liter (NS) in the obese and type 2 diabetic subjects, respectively. The glucose infusion rate during steady-state hyperinsulinemia was 10.8 +/- 0.8 and 7.2 +/- 0.4 mg/kg.min in the obese and diabetic subjects, respectively (P < 0.01). Interstitial-arterial lactate difference was significantly higher in the obese subjects. During steady-state hyperinsulinemia, PS for glucose was significantly higher in the obese subjects (1.1 +/- 0.2 vs. 0.5 +/- 0.1 ml/min.100 g, P < 0.05). Glucose uptake was also significantly higher in the obese subjects (3.0 +/- 0.4 vs. 1.8 +/- 0.3 mumol/min.100 g, P < 0.05). During steady-state hyperinsulinemia, PS for insulin was 0.4 +/- 0.1 and 0.3 +/- 0.1 ml/min.100 g in the obese and diabetic subjects, respectively (NS), and insulin uptake was 258 +/- 54 vs. 168 +/- 24, respectively (NS). When both subject groups were pooled together, a significant correlation was found between PS for glucose and glucose uptake during steady-state hyperinsulinemia. Skeletal muscle blood flow during steady-state hyperinsulinemia was 1.9 +/- 0.2 and 2.3 +/- 0.4 ml/100 g.min in the obese and diabetic subjects, respectively (NS). Blood flow did not increase during hyperinsulinemia in either of the two groups. The present data clearly show that PS for glucose is subnormal during steady-state hyperinsulinemia in insulin-resistant type 2 diabetic subjects. Furthermore, there was a close correlation between glucose uptake and PS for glucose but not between blood flow and PS. We suggest that PS is a more sensitive marker for insulin resistance during hyperinsulinemia than limb flow. The lower capacity for transcapillary passage found in the type 2 diabetic subjects is suggested to further aggravate insulin resistance.

Delayed transcapillary delivery of insulin to muscle interstitial fluid after oral glucose load in obese subjects.

Obese subjects exhibit a delay in insulin action and delivery of insulin to muscle interstitial fluid during glucose/insulin infusion. The aim of the present study was to follow the distribution of insulin to skeletal muscle after an oral glucose load in obese subjects. We conducted an oral glucose tolerance test (OGTT) in 10 lean and 10 obese subjects (BMI 23 +/- 0.6 vs. 33 +/- 1.2 kg/m(2); P < 0.001). Insulin measurements in muscle interstitial fluid were combined with forearm arteriovenous catheterization and blood flow measurements. In the obese group, interstitial insulin was significantly (35-55%) lower than plasma insulin (P < 0.05) during the 1st h after the OGTT, whereas in lean subjects, no significant difference was found between interstitial and plasma insulin levels during the same time period. The permeability surface area product for glucose, representing capillary recruitment, increased in the lean group (P < 0.05) but not in the obese group (NS). Obese subjects had a significantly higher plasma insulin level at 90-120 min after oral glucose (398 +/- 57 vs. 224 +/- 37 pmol/l in control subjects; P < 0.05). The significant gradient between plasma insulin and muscle interstitial insulin during the first hour after OGTT suggests a slow delivery of insulin in obese subjects. The hindered transcapillary transport of insulin may be attributable to a defect in insulin-mediated capillary recruitment.

Direct measurements of the permeability surface area for insulin and glucose in human skeletal muscle.

To elucidate mechanisms regulating capillary transport of insulin and glucose, we directly calculated the permeability surface (PS) area product for glucose and insulin in muscle. Intramuscular microdialysis in combination with the forearm model and blood flow measurements was performed in healthy males, studied during an oral glucose tolerance test or during a one-step or two-step euglycemic hyperinsulinemic clamp. PS for glucose increased significantly from 0.29 +/- 0.1 to 0.64 +/- 0.2 ml/min.100 g after oral glucose tolerance test, and glucose uptake increased from 1.2 +/- 0.4 to 2.6 +/- 0.6 micro mol/min.100 g (P < 0.05). During one-step hyperinsulinemic clamp (plasma insulin, 1.962 pmol/liter), PS for glucose increased from 0.2 +/- 0.1 to 2.3 +/- 0.9 ml/min.100 g (P < 0.05), and glucose uptake increased from 0.6 +/- 0.2 to 5.0 +/- 1.4 micro mol/min.100 g (P < 0.05). During the two-step clamp (plasma insulin, 1380 +/- 408 and 3846 +/- 348 pmol/liter), the arterial-interstitial difference and PS for insulin were constant. The PS for glucose tended to increase (P = not significant), whereas skeletal muscle blood flow increased from 4.4 +/- 0.7 to 6.2 +/- 0.8 ml/min.100 ml (P < 0.05). The present data show that PS for glucose is markedly increased by oral glucose, whereas a further vasodilation exerted by high insulin concentrations may not be physiologically relevant for capillary delivery of either glucose or insulin in resting muscle.

Myocardial interstitial glucose and lactate before, during, and after cardioplegic heart arrest.

The interstitial fluid of the human myocardium was monitored in 13 patients undergoing aortic valve and/or bypass surgery before, during, and after hypothermic potassium cardioplegia. The regulation of glucose and lactate was studied after sampling with microdialysis. The following questions were addressed. 1). Is the rate of transcapillary diffusion the limiting step for myocardial uptake of glucose before or after cardioplegia? 2). Does cold potassium cardioplegia induce a critical deprivation of glucose and/or accumulation of lactate in the myocardium? Before cardioplegia, interstitial glucose was approximately 50% of the plasma level (P < 0.001). Interstitial glucose decreased significantly immediately after induction of cardioplegia and remained low (1.25 +/- 0.25 mM) throughout cardioplegia. It was restored to precardioplegic levels 1 h after release of the aortic clamp. Interstitial glucose then decreased again at 25 and 35 h postoperatively to the levels observed during cardioplegia. Interstitial lactate decreased immediately after induction of cardioplegia but returned to basal level during the clamping period. At 25 and 35 h, interstitial lactate was significantly lower than before and during cardioplegia. Glucose transport over the capillary endothelium is considered rate limiting for its uptake in the working heart but not during cold potassium cardioplegia despite the glucose deprivation following perfusion of glucose-free cardioplegic solution. Lactate accumulated during cardioplegia but never reached exceedingly high interstitial levels. We conclude that microdialysis provides information that may be relevant for myocardial protection during open-heart surgery.

Delayed transcapillary transport of insulin to muscle interstitial fluid in obese subjects.

Insulin-resistant subjects have a slow onset of insulin action, and the underlying mechanism has not been determined. To evaluate whether a delayed transcapillary transport is part of the peripheral insulin resistance, we followed the kinetics of infused insulin and inulin in plasma and muscle interstitial fluid in obese insulin-resistant patients and control subjects. A total of 10 lean and 10 obese men (BMI 24 +/- 0.8 vs. 32 +/- 0.8 kg/m(2), P < 0.001) was evaluated during a hyperinsulinemic-euglycemic clamp (insulin infusion rate 120 mU. m(-2). min(-1)) combined with an inulin infusion. Measurements of insulin and inulin in plasma were taken by means of arterial-venous catheterization of the forearm and microdialysis in brachioradialis muscle combined with forearm blood flow measurements with vein occlusion pletysmography. The obese subjects had a significantly lower steady-state glucose infusion rate and, moreover, demonstrated a delayed appearance of insulin (time to achieve half-maximal concentration [T(1/2)] 72 +/- 6 vs. 46 +/- 6 min in control subjects, P < 0.05) as well as inulin (T(1/2) 83 +/- 3 vs. 53 +/- 7 min, P < 0.01) in the interstitial fluid. Also, the obese subjects had a delayed onset of insulin action (T(1/2) 70 +/- 9 vs. 45 +/- 5 min in control subjects, P < 0.05), and their forearm blood flow rate was significantly lower. These results demonstrate a delayed transcapillary transport of insulin and inulin from plasma to the muscle interstitial fluid and a delayed onset of insulin action in insulin-resistant obese subjects.

Measurements of interstitial muscle glycerol in normal and insulin-resistant subjects.

The aim of this project was to study the regulation of interstitial glycerol levels in muscle in normal subjects, and to estimate interstitial muscle glycerol in obese subjects and patients with type 2 diabetes. In healthy lean subjects, microdialysis of forearm sc and muscle tissue were combined with arterial and deep venous catheterization, as well as blood flow registrations during oral glucose ingestion. In two other separate studies, obese (n = 9) vs. lean (n = 10) subjects and type 2 diabetes patients (n = 8) vs. weight-matched control subjects (n = 8) were investigated by means of muscle microdialysis during a euglycemic hyperinsulinemic clamp. Oral glucose ingestion suppressed the interstitial sc glycerol concentration by approximately 40% (P < 0.05), whereas no significant reduction of muscle interstitial glycerol was found. In contrast to the significant muscle interstitial-arterial (I-A) glycerol difference, the venous-arterial difference was small and varying throughout the oral glucose tolerance test. At steady-state hyperinsulinemia, obese subjects' interstitial muscle glycerol and I-A glycerol difference were both significantly higher than lean controls, whereas type 2 diabetes patient had interstitial muscle glycerol concentrations and I-A glycerol differences similar to those found in weight-matched controls. A significant and marked I-A glycerol difference exists in the absence of a significant venous-arterial difference, indicating that muscle glycerol cannot be taken as a marker of intramyocellular lipolysis because local turnover of muscle glycerol might be significant. The present data also suggest that, in contrast to sc tissue, muscle tissue lacks a clear antilipolytic effect of insulin. Moreover, the muscle interstitial glycerol concentration is elevated in obese patients but does not precipitate insulin resistance and type 2 diabetes.