CB(1) blockade-induced weight loss over 48 weeks decreases liver fat in proportion to weight loss in humans.

OBJECTIVE: Studies in mice have suggested that endocannabinoid blockade using the cannabinoid receptor type 1 (CB1) blocker rimonabant prevents obesity-induced hepatic steatosis. DESIGN AND SUBJECTS: To determine effects of rimonabant on liver fat in humans, we measured liver fat content by proton magnetic resonance spectroscopy in 37 subjects who used either a CB1 blocker rimonabant or placebo in a double-blind, randomized manner. This was retrospectively compared with a historical hypocaloric diet weight loss group (n=23). RESULTS: Weight loss averaged 8.5±1.4 kg in the rimonabant, 1.7±1.0 kg in the placebo and 7.5±0.2 kg in the hypocaloric diet group (P<0.001, rimonabant vs placebo; NS, rimonabant vs hypocaloric diet). Liver fat decreased more in the rimonabant (5.9% (2.5-14.6%) vs 1.8% (0.9-3.5%), before vs after) than in the placebo group (6.8% (2.2-15.7%) vs 4.9% (1.6-7.8%), before vs after, P<0.05). The percentage change in body weight correlated closely with the percentage loss of liver fat (r=0.70, P>0.0001). The decreases in liver fat were comparable between the rimonabant and the young historical hypocaloric diet groups. CONCLUSIONS: We conclude that, unlike in mice, in humans rimonabant decreases liver fat in proportion to weight loss.

Serum saturated fatty acids containing triacylglycerols are better markers of insulin resistance than total serum triacylglycerol concentrations.

AIMS/HYPOTHESIS: The weak relationship between insulin resistance and total serum triacylglycerols (TGs) could be in part due to heterogeneity of TG molecules and their distribution within different lipoproteins. We determined concentrations of individual TGs and the fatty acid composition of serum and major lipoprotein particles and analysed how changes in different TGs and fatty acid composition are related to features of insulin resistance and abdominal obesity. METHODS: We performed lipidomic analyses of all major lipoprotein fractions using two analytical platforms in 16 individuals, who exhibited a broad range of insulin sensitivity. RESULTS: We identified 45 different TGs in serum. Serum TGs containing saturated and monounsaturated fatty acids were positively, while TGs containing essential linoleic acid (18:2 n-6) were negatively correlated with HOMA-IR. Specific serum TGs that correlated positively with HOMA-IR were also significantly positively related to HOMA-IR when measured in very-low-density lipoproteins (VLDLs), intermediate-density lipoproteins (IDLs) and LDL, but not in HDL subfraction 2 (HDL(2)) or 3 (HDL(3)). Analyses of proportions of esterified fatty acids within lipoproteins revealed that palmitic acid (16:0) was positively related to HOMA-IR when measured in VLDL, IDL and LDL, but not in HDL(2) or HDL(3). Monounsaturated palmitoleic (16:1 n-7) and oleic (18:1 n-9) acids were positively related to HOMA-IR when measured in HDL(2) and HDL(3), but not in VLDL, IDL or LDL. Linoleic acid was negatively related to HOMA-IR in all lipoproteins. CONCLUSIONS/INTERPRETATION: Serum concentrations of specific TGs, such as TG(16:0/16:0/18:1) or TG(16:0/18:1/18:0), may be more precise markers of insulin resistance than total serum TG concentrations.

A common variant in PNPLA3, which encodes adiponutrin, is associated with liver fat content in humans.

AIMS/HYPOTHESIS: It has recently been suggested that the rs738409 G allele in PNPLA3, which encodes adiponutrin, is strongly associated with increased liver fat content in three different ethnic groups. The aims of the present study were as follows: (1) to try to replicate these findings in European individuals with quantitative measures of hepatic fat content; (2) to study whether the polymorphism influences hepatic and adipose tissue insulin sensitivity; and (3) to investigate whether PNPLA3 expression is altered in the human fatty liver. METHODS: We genotyped 291 Finnish individuals in whom liver fat had been measured using proton magnetic resonance spectroscopy. Hepatic PNPLA3 expression was measured in 32 participants. Hepatic and adipose tissue insulin sensitivities were measured using a euglycaemic-hyperinsulinaemic (insulin infusion 0.3 mU kg(-1) min(-1)) clamp technique combined with infusion of [3-(3)H]glucose in 109 participants. RESULTS: The rs738409 G allele in PNPLA3 was associated with increased quantitative measures of liver fat content (p = 0.011) and serum aspartate aminotransferase concentrations (p = 0.002) independently of age, sex and BMI. Fasting serum insulin and hepatic and adipose tissue insulin sensitivity were related to liver fat content independently of genotype status. PNPLA3 mRNA expression in the liver was positively related to obesity (r = 0.62, p < 0.0001) and to liver fat content (r = 0.58, p = 0.025) in participants who were not morbidly obese (BMI < 40 kg/m(2)). CONCLUSIONS/INTERPRETATION: A common variant in PNPLA3 increases the risk of hepatic steatosis in humans.

Differential effects of oral and transdermal estrogen replacement therapy on endothelial function in postmenopausal women.

BACKGROUND: We determined whether the vascular effects of estradiol depend on the route of administration by comparing the effects of oral estradiol and transdermal placebo, transdermal estradiol and oral placebo, and transdermal placebo and oral placebo on in vivo endothelial function in 27 postmenopausal women. METHODS AND RESULTS: Endothelial function was assessed from blood flow responses to intrabrachial artery infusions of endothelium-dependent (7.5 and 15 microgram/min acetylcholine) and endothelium-independent (3 and 10 microgram/min of sodium nitroprusside) vasodilators at 0, 2, and 12 weeks. In the oral estradiol group, the increase in flow above basal during infusion of the low dose of acetylcholine at 0, 2, and 12 weeks averaged 6.0+/-0.8, 6.9+/-0.8, and 11.3+/-1.2 (P<0.01 versus 0 and 2 weeks) mL. dL(-1). min(-1) at 0, 2, and 12 weeks. The percentage increases versus 0 weeks averaged 21+/-14% at 2 and 120+/-34% at 12 weeks. During the high-dose acetylcholine infusion, the increase in flow above basal averaged 8.6+/-1.3, 10.2+/-1.5, and 15.1+/-1.8 (P<0.05 versus 0 weeks) mL. dL(-1). min(-1), respectively. The percentage increases versus 0 weeks averaged 22+/-10% at 2 weeks and 119+/-46% at 12 weeks. In the oral estradiol group, endothelium-independent vasodilatation also improved significantly, but less markedly than endothelium-dependent responses. In the transdermal and placebo groups, all vascular responses remained unchanged. Oral but not transdermal estradiol also induced significant decreases in LDL cholesterol and Lp(a) concentrations and an increase in HDL cholesterol within 2 weeks. CONCLUSIONS: We conclude that oral but not transdermal estradiol induces potentially antiatherogenic changes in in vivo endothelium-dependent vasodilatation and lipid concentrations.

Marked resistance of the ability of insulin to decrease arterial stiffness characterizes human obesity.

We tested the hypothesis that insulin has effects on large artery stiffness in addition to its slow vasodilatory effect on resistance vessels in skeletal muscle, and whether such an effect might be altered in obesity. Eight nonobese (aged 25 +/- 1 years, BMI 22.7 +/- 0.4 kg/m2) and eight obese (aged 27 +/- 2 years, BMI 30.6 +/- 0.9 kg/m2) men were studied under normoglycemic-hyperinsulinemic (sequential 2-h insulin infusions of 1 [step 1] and 2 [step 2] mU x kg(-1) x min(-1)) conditions, and another seven men participated in a saline control study. Central aortic pressure waves were synthesized from those recorded in the periphery using applanation tonometry and a validated reverse transfer function every 30 min. This allowed determination of augmentation (the pressure difference between early and late systolic pressure peaks) and the augmentation index (augmentation divided by pulse pressure), a measure of arterial stiffness. Whole-body glucose uptake was reduced by 48 (step 1) and 41% (step 2) (P < 0.01) in the obese subjects versus the nonobese subjects. Basal forearm blood flow averaged 2.5 +/- 0.2 and 2.6 +/- 0.2 ml x dl(-1) x min(-1) in the obese and nonobese subjects, respectively (NS). Insulin induced a significant increase in forearm blood flow after 2.5 h (3.6 +/- 0.4 ml x dl(-1) x min(-1), P < 0.05 vs. basal) in the nonobese subjects and after 4 h in the obese subjects (3.2 +/- 0.2, P < 0.05). In contrast to these slow changes in peripheral blood flow, augmentation and the augmentation index decreased significantly in the nonobese subjects after 1 h (-3.0 +/- 1.6 mmHg and -10.0 +/- 5.4%, respectively, P < 0.001 vs. basal), but remained unchanged until 3 h in the obese subjects. Percent fat (r = 0.86, P < 0.0001) and whole-body glucose uptake (r = -0.72, P < 0.01) correlated with the change in the augmentation index by insulin. These data demonstrate temporal dissociation in insulin's vascular actions. Insulin's effect to decrease arterial stiffness in nonobese subjects (a decrease in wave reflection) is observed under physiological conditions and precedes a slow vasodilatory effect in the periphery. In the obese subjects, insulin's normal effect to decrease central wave reflection is severely blunted. The degree of impairment in this novel vascular action of insulin is closely correlated with the degree of obesity and insulin action on glucose uptake.

Predictors of abnormal cardiovascular autonomic function measured by frequence domain analysis of heart rate variability and conventional tests in patients with type 1 diabetes.

OBJECTIVE: Frequency domain analysis of heart rate variability (HRV) is used to assess cardiovascular autonomic function. There are no prospective data on the sensitivity of its various components to glycemia or other diabetes-related risk factors compared with conventional tests and with other complications of diabetes. RESEARCH DESIGN AND METHODS: In 1985, possible risk factors of future complications were determined in 115 children with type 1 diabetes. In 1996, the presence of complications (HRV analysis, conventional tests of autonomic function, urinary albumin excretion rate [UAER], and retinopathy) were assessed in 83 of these patients (age 32 +/- 1 years, duration of diabetes 22 +/- 1 years). RESULTS: Poor glycemic control (measured as lifetime glycemic exposure or HbA1c in 1985) was the most important independent predictor of decreases in all measures of absolute power of HRV (total power [TP] and very low frequency, low frequency [LF], and high frequency [HF] power) and square root of the mean square of R-R interval differences but not of changes of normalized measures or ratios (normalized HF and LF LF/HF). Other significant independent predictors of autonomic dysfunction were late age of onset of diabetes, female sex, and high BMI. To examine the sensitivity of the various tests to glycemia, the patients were divided into tertiles based on lifetime glycemic exposure (A1c months). Glycemic exposure in the tertiles averaged 194 +/- 25 A1c months (20 years of HbA1c 0.8% above normal), 556 +/- 19 A1c months(20 years of HbA1c 2.3% above normal), and 963 +/- 30 A1c months (20 years of HbA1c 4% above normal). Tests of complications that were significantly abnormal in patients already in the lowest tertile and were correlated with glycemia were TP and severity of retinopathy. Of conventional tests, only the ratio of length of R-R intervals during expiration to inspiration (E/I ratio) was significantly related to glycemic exposure, but it required high glycemic exposure (20 years of HbA1c 4% above normal) to be abnormal. UAER was significantly increased only in the highest tertile of glycemic exposure. CONCLUSIONS: TP and retinopathy score were much more sensitive to antecedent glycemia than conventional tests of autonomic function or UAER and were significantly abnormal in patients exposed to approximately 20 years' duration of an HbA1c 0.8% above normal.

Impaired endothelium-dependent vasodilation in type 2 diabetes. Relation to LDL size, oxidized LDL, and antioxidants.

OBJECTIVE: To search for determinants of endothelial dysfunction in type 2 diabetes. RESEARCH DESIGN AND METHODS: We performed a comprehensive analysis of cardiovascular risk markers and measured blood flow responses to endothelium-dependent (acetylcholine [ACh] and NG-monomethyl-L-arginine) and -independent (sodium nitroprusside [SNP]) vasoactive agents in 30 nonsmoking men with type 2 diabetes (age 51 +/- 1 years, BMI 27.8 +/- 0.4 kg/m2, HbA1c 7.4 +/- 0.3%) and 12 matched normal control men. RESULTS: ACh-induced vasodilation was 37% lower in type 2 diabetic (6.1 +/- 0.5) than in normal subjects (9.7 +/- 1.5 ml.dl-1.min-1, P < 0.01), while flows during SNP were similar (9.1 +/- 0.6 vs. 9.9 +/- 1.3 ml.dl-1.min-1, NS). The ratio of endothelium-dependent vs. -independent flow (ACh:SNP ratio) was 31% lower in type 2 diabetic (0.70 +/- 0.05) than in normal subjects (1.10 +/- 0.18, P < 0.01). Total (2.2 +/- 0.4 vs. 1.3 +/- 0.2 mmol/l, P < 0.05), VLDL, and intermediate-density lipoprotein triglycerides were significantly higher, and the mean LDL particle diameter was significantly smaller in type 2 diabetic than in normal subjects. The lag times for LDL oxidation by Cu2+ in vitro were similar in patients with type 2 diabetes (183 +/- 7) and in normal subjects (183 +/- 9 min, NS). Measured and calculated (sum of concentration of individual antioxidants in serum) total peroxyl radical-trapping capacities (TRAPs) were comparable between the groups. In the patients with type 2 diabetes, LDL size was significantly correlated with endothelium-dependent vasodilation (r = 0.43, P < 0.05), serum triglycerides (r = -0.75, P < 0.001), and the lag time for LDL oxidation in vitro (r = 0.38, P < 0.05). HbA1c was inversely correlated with the lag time for LDL oxidation in vitro (r = -0.41, P < 0.05) and TRAP. CONCLUSIONS: In summary, patients with type 2 diabetes exhibited impaired endothelium-dependent vasodilation in vivo, elevated serum triglycerides, decreased LDL size, and normal antioxidant capacity. Of these parameters, LDL size was significantly correlated with endothelial function.

Insulin sensitivity regulates autonomic control of heart rate variation independent of body weight in normal subjects.

It is unclear whether insulin sensitivity independent of body weight regulates control of heart rate variation (HRV) by the autonomic nervous system. Insulin action on whole-body glucose uptake (M-value) and heart rate variability were measured in 21 normal men. The subjects were divided into 2 groups [normally insulin sensitive (IS, 8.0 +/- 0.4 mg/kg.min) and less insulin sensitive (IR, 5.1 +/- 0.3 mg/kg.min)] based on their median M-value (6.2 mg/kg x min). Spectral power analysis of heart rate variability was performed in the basal state and every 30 min during the insulin infusion. The IS and IR groups were comparable, with respect to age (27 +/- 2 vs. 26 +/- 2 yr), body mass index (22 +/- 1 vs. 23 +/- 1 kg/m(2)), body fat (13 +/- 1 vs. 13 +/- 1%), systolic (121 +/- 16 vs. 117 +/- 14 mm Hg) and diastolic (74 +/- 11 vs. 73 +/- 11 mm Hg) blood pressures, and fasting plasma glucose (5.4 +/- 0.1 vs. 5.5 +/- 0.1 mmol/L) concentrations. Fasting plasma insulin was significantly higher in the IR (30 +/- 4 pmol/L) than in the IS (17 +/- 3 pmol/L, P < 0.05) group. In the IS group, insulin significantly increased the normalized low-frequency (LFn) component, a measure of predominantly sympathetic nervous system activity, from 36 +/- 5 to 48 +/- 4 normalized units (nu; 0 vs. 30-120 min, P < 0.001); whereas the normalized high-frequency (HFn) component, a measure of vagal control of HRV, decreased from 66 +/- 9 to 48 +/- 5 nu (P < 0.001). No changes were observed in either the normalized LF component [35 +/- 5 vs. 36 +/- 2 nu, not significant (NS)] or the normalized HF component (52 +/- 6 vs. 51 +/- 4 nu, NS) in the IR group. The ratio LF/HF, a measure of sympathovagal balance, increased significantly in the IS group (0.92 +/- 0.04 vs. 1.01 +/- 0.04, P < 0.01) but remained unchanged in the IR group (0.91 +/- 0.04 vs. 0.92 +/- 0.03, NS). Heart rate and systolic and diastolic blood pressures remained unchanged during the insulin infusion in both groups. We conclude that insulin acutely shifts sympathovagal control of HRV toward sympathetic dominance in insulin-sensitive, but not in resistant, subjects. These data suggest that sympathetic overactivity is not a consequence of hyperinsulinemia.

Autoantibodies against oxidized LDL and endothelium-dependent vasodilation in insulin-dependent diabetes mellitus.

We determined whether autoantibodies against oxidized LDL are increased in patients with IDDM, and if so, whether they are associated with endothelial dysfunction in vivo. Autoantibodies against oxidized LDL (ratio of antibodies against oxidized vs. native LDL, oxLDLab) were determined in 38 patients with IDDM (HbA(1c) 8.4+/-0.2%), who were clinically free of macrovascular disease, and 33 healthy normolipidemic subjects (HbA(1c) 5.1+/-0.1%, P<0.001 vs. IDDM). The groups had comparable serum total-, LDL- (2. 9+/-0.1 vs. 2.8+/-0.1 mmol/l, IDDM vs. controls), and HDL-cholesterol concentrations. OxLDLab were 1.5-fold higher in the IDDM patients (1.8+/-0.1) than in the normal subjects (1.2+/-0.1, P<0.001). OxLDLab were correlated with age in normal subjects, but not with age, duration of disease, LDL-cholesterol, HbA(1c) or degree of microvascular complications in patients with IDDM. To determine whether oxLDLab are associated with endothelial dysfunction in vivo, blood flow responses to intrabrachial infusions of acetylcholine, sodium nitroprusside and L-NMMA were determined in 23 of the patients with IDDM (age 33+/-1 years, body mass index 24. 3+/-0.6 kg/m(2), HbA(1c) 8.5+/-0.3%) and in the 33 matched normal males. OxLDLab were 41% increased in IDDM (1.7+/-0.2 vs. 1.2+/-0.1, P<0.01). Within the group of IDDM patients, HbA(1c) but not oxLDLab or LDL-cholesterol, was inversely correlated with the forearm blood flow response to acetylcholine (r=-0.51, P<0.02), an endothelium-dependent vasodilator, but not to sodium nitroprusside (r=0.06, NS). These data demonstrate that oxLDLab concentrations are increased in patients with IDDM, but show that chronic hyperglycemia rather than oxLDLab, is associated with impaired endothelium-dependent vasodilation in these patients.

Intense physical training decreases circulating antioxidants and endothelium-dependent vasodilatation in vivo.

Physical training increases free radical production and consumes antioxidants. It has previously been shown that acute exercise markedly increases the susceptibility of LDL to oxidation but whether such changes are observed during physical training is unknown. We measured circulating antioxidants, lipids and lipoproteins, and blood flow responses to intrabrachial infusions of endothelium-dependent (acetylcholine, ACh, L-N-monomethyl-arginine, L-NMMA) and -independent (sodium nitroprusside, SNP) vasoactive agents, before and after 3 months of running in 9 fit male subjects. Maximal aerobic power increased from 53 +/- 1 to 58 +/- 2 ml/kg min (P < 0.02). All circulating antioxidants (uric acid, SH-groups, alpha-tocopherol, beta-carotene, retinol) except ascorbate decreased significantly during training. Endothelium-dependent vasodilatation in forearm vessels decreased by 32-35% (P < 0.05), as determined from blood flow responses to both a low (10.8 +/- 2.1 vs. 7.3 +/- 1.5 ml/dl min, 0 vs. 3 months) and a high (14.8 +/- 2.6 vs. 9.6 +/- 1.8) ACh dose. The % endothelium-dependent blood flow (% decrease in basal flow by L-NMMA), decreased through training from 37 +/- 3 to 22 +/- 7% (P < 0.05). Blood flow responses to SNP remained unchanged. The decrease in uric acid was significantly correlated with the change in the % decrease in blood flow by L-NMMA (r = 0.74, P < 0.05). The lag time for the susceptibility of plasma LDL to oxidation in vitro, LDL size and the concentration of LDL cholestetol remained unchanged. We conclude that relatively intense aerobic training decreases circulating antioxidant concentrations and impairs endothelial function in forearm vessels.

Tissue specificity of insulin resistance in humans: fat in the liver rather than muscle is associated with features of the metabolic syndrome.

AIMS/HYPOTHESIS: The aim of this study was to investigate whether intrahepatic and intramyocellular fat are related to insulin resistance in these respective tissues or to the metabolic syndrome. METHODS: Hepatic (insulin 1.8 pmol kg(-1) min(-1) combined with [3-3H]glucose) and muscle (insulin 6.0 pmol kg(-1) min(-1)) insulin sensitivity were measured on separate occasions in 45 non-diabetic men (age 42 +/- 1 years, BMI 26.2 +/- 0.6 kg/m2) using the euglycaemic-hyperinsulinaemic clamp. Liver fat and intramyocellular lipid (IMCL) were measured by proton magnetic resonance spectroscopy and body composition by magnetic resonance imaging. We also determined fasting serum insulin and adiponectin concentrations, components of the metabolic syndrome and maximal oxygen consumption. RESULTS: In participants with high [median 12.0% (interquartile range 5.7-18.5%)] vs low [2.0% (1.0-2.0%)] liver fat, fasting serum triacylglycerols (1.6 +/- 0.2 vs 1.0 +/- 0.1 mmol/l, p = 0.002) and fasting serum insulin (55 +/- 4 vs 32 +/- 2 pmol/l, p < 0.0001) were increased and serum HDL-cholesterol (1.26 +/- 0.1 vs 1.48 +/- 0.1 mmol/l, p = 0.02) and fasting serum adiponectin (9.5 +/- 1.2 vs 12.2 +/- 1.2 microg/ml, p = 0.05) decreased. In participants with high [19.5% (16.0-26.0%)] vs low [5.0% (2.3-7.5%)] IMCL, these parameters were comparable. Liver fat was higher in participants with [10.5% (3.0-18.0%)] than in those without [2.0% (1.5-6.0%), p = 0.010] the metabolic syndrome, even independently of obesity, while IMCL was comparable. Insulin suppression of glucose rate of appearance and serum NEFA was significantly impaired in the high liver fat group. CONCLUSIONS/INTERPRETATION: Fat accumulation in the liver rather than in skeletal muscle is associated with features of the metabolic syndrome, i.e. increased fasting serum triacylglycerols and decreased fasting serum HDL-cholesterol, as well as with hyperinsulinaemia and low adiponectin.

Increased inflammatory activity parallels increased basal nitric oxide production and blunted response to nitric oxide in vivo in rheumatoid arthritis.

BACKGROUND: Endothelial dysfunction, defined as loss of bioactivity of NO in the vessel wall, is thought to precede atherosclerosis. OBJECTIVE: To determine whether endothelial dysfunction characterises patients with RA and whether these patients have increased inducible nitric oxide synthase (iNOS) dependent NO production in vivo. METHODS: and results: Twenty patients with RA and 33 normal subjects received intrabrachial artery infusions of endothelium dependent (acetylcholine (ACh)) and independent (sodium nitroprusside (SNP)) vasodilators to determine arterial responsiveness to NO. Basal flow and its percentage decrease by NG-monomethyl-L-arginine (L-NMMA), an inhibitor of both iNOS and endothelium dependent NOS (eNOS), was used to determine the contribution of iNOS and eNOS dependent NO to basal flow. Both SNP (p<0.01) and ACh (p<0.05) increased blood flow significantly less in patients with RA than normal subjects. Serum concentrations of TNFalpha were, within the RA group, inversely correlated with blood flow responses to both SNP (r=-0.67, p=0.002) and ACh (r=-0.64, p<0.005). Basal flow was significantly increased in RA and correlated within this group with serum CRP (r=0.48, p<0.05), TNFalpha (r=0.61, p<0.01) concentrations, and ESR (r=0.68, p<0.002). L-NMMA decreased basal flow significantly more (-34+/-2%) in the patients with RA than the normal subjects (-24+/-3%, p<0.02), suggesting in view of the blunted response to ACh, increased iNOS activity. CONCLUSIONS: Patients with RA have a dual abnormality in NO dependent vascular function. Basal blood flow is increased in proportion to inflammatory activity and more inhibited by L-NMMA, suggesting increased iNOS activity, and responsiveness to NO is reduced.

Dissociation between insulin sensitivity of glucose uptake and endothelial function in normal subjects.

Insulin increases limb blood flow in a time- and dose-dependent manner. This effect can be blocked by inhibiting nitric oxide synthesis. These data raise the possibility that insulin resistance is associated with endothelial dysfunction. To examine whether endothelial function and insulin sensitivity are interrelated we quantitated in vivo insulin-stimulated rates of whole body and forearm glucose uptake at a physiological insulin concentration (euglycaemic hyperinsulinaemic clamp, 1 mU.kg-1.min-1 insulin infusion for 2 h) and on another occasion, in vivo endothelial function (blood flow response to intrabrachial infusions of sodium nitroprusside, acetylcholine, and N-monomethyl-L-arginine) in 30 normal male subjects. Subjects were divided into an insulin-resistant (IR) and an insulin-sensitive (IS) group based on the median rate of whole body glucose uptake (31 +/- 2 vs 48 +/- 1 mumol.kg-1.min-1, p < 0.001). The IR and IS groups were matched for age, but the IR group had a slightly higher body mass index, percentage of body fat and blood pressure compared to the IS group. The IR group also had diminished insulin-stimulated glucose extraction (p < 0.05) compared to the IS group, while basal and insulin-stimulated forearm blood flow rates were identical. There was no difference between the IR and IS groups in the forearm blood flow response to endothelium-dependent (acetylcholine and N-monomethyl-L-arginine) or -independent (sodium nitroprusside) vasoactive drugs. In conclusion, the ability of insulin to stimulate glucose uptake at physiological insulin concentrations and endothelium-dependent vasodilatation are distinct phenomena and do not necessarily coexist.

A marathon run increases the susceptibility of LDL to oxidation in vitro and modifies plasma antioxidants.

Physical activity increases the production of oxygen free radicals, which may consume antioxidants and oxidize low-density lipoprotein (LDL). To determine whether this occurs during strenuous aerobic exercise, we studied 11 well-trained runners who participated in the Helsinki City Marathon. Blood samples were collected before, immediately after, and 4 days after the race to determine its effect on circulating antioxidants and LDL oxidizability in vitro. LDL oxidizability was increased as determined from a reduction in the lag time for formation of conjugated dienes both immediately after (180 +/- 7 vs. 152 +/- 4 min, P < 0.001) and 4 days after (155 +/- 7 min, P < 0.001) the race. No significant changes in lipid-soluble antioxidants in LDL or in the peak LDL particle size were observed after the race. Total peroxyl radical trapping antioxidant capacity of plasma (TRAP) and uric acid concentrations were increased after the race, but, except for TRAP, these changes disappeared within 4 days. Plasma thiol concentrations were reduced after the race. No significant changes were observed in plasma ascorbic acid, alpha-tocopherol, beta-carotene, and retinol concentrations after the marathon race. We conclude that strenuous aerobic exercise increases the susceptibility of LDL to oxidation in vitro for up to 4 days. Although the increase in the concentration of plasma TRAP reflects an increase of plasma antioxidant capacity, it seems insufficient to prevent the increased susceptibility of LDL to oxidation in vitro, which was still observed 4 days after the race.