Raffaele Marfella

Inflammatory Cytokine Concentrations Are Acutely Increased by Hyperglycemia in Humans Role of Oxidative Stress

Background—Circulating levels of interleukin-6 (IL-6) and tumor necrosis factor-&agr; (TNF-&agr;) are elevated in diabetic patients. We assessed the role of glucose in the regulation of circulating levels of IL-6, TNF-&agr;, and interleukin-18 (IL-18) in subjects with normal or impaired glucose tolerance (IGT), as well as the effect of the antioxidant glutathione. Methods and Results—Plasma glucose levels were acutely raised in 20 control and 15 IGT subjects and maintained at 15 mmol/L for 5 hours while endogenous insulin secretion was blocked with octreotide. In control subjects, plasma IL-6, TNF-&agr;, and IL-18 levels rose (P <0.01) within 2 hours of the clamp and returned to basal values at 3 hours. In another study, the same subjects received 3 consecutive pulses of intravenous glucose (0.33 g/kg) separated by a 2-hour interval. Plasma cytokine levels obtained at 3, 4, and 5 hours were higher (P <0.05) than the corresponding values obtained during the clamp. The IGT subjects had fasting plasma IL-6 and TNF-&agr; levels higher (P <0.05) than those of control subjects. The increase in plasma cytokine levels during the clamping lasted longer (4 hours versus 2 hours, P <0.01) in the IGT subjects than in the control subjects, and the cytokine peaks of IGT subjects after the first glucose pulse were higher (P <0.05) than those of control subjects. On another occasion, 10 control and 8 IGT subjects received the same glucose pulses as above during an infusion of glutathione; plasma cytokine levels did not show any significant change from baseline after the 3 glucose pulses. Conclusions—Hyperglycemia acutely increases circulating cytokine concentrations by an oxidative mechanism, and this effect is more pronounced in subjects with IGT. This suggests a causal role for hyperglycemia in the immune activation of diabetes.

Postprandial endothelial activation in healthy subjects and in type 2 diabetic patients: role of fat and carbohydrate meals.

OBJECTIVES To compare the effect of a high-fat meal and a high-carbohydrate meal (pizza), with and without antioxidant vitamins, on endothelial activation in healthy subjects and in patients with type 2 diabetes mellitus. BACKGROUND The postprandial state is becoming increasingly acknowledged to affect some early events of atherogenesis. METHODS In a randomized, observer-blinded, crossover study, 20 newly diagnosed type 2 diabetic patients and 20 age- and gender-matched healthy subjects received two meals at one-week intervals: a high-fat meal (760 calories) and an isoenergetic high-carbohydrate meal (non-cheese pizza). In all subjects, the same meals were repeated immediately following ingestion of vitamin E, 800 IU, and ascorbic acid, 1,000 mg. RESULTS In normal subjects, the high-fat meal increased the plasma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), which were prevented by vitamins. No change in these parameters occurred after pizza ingestion or pizza ingestion with vitamins. In diabetic patients, basal concentrations of glucose, cytokines and adhesion molecules were significantly higher than in nondiabetic controls. Both meals significantly increased cytokine and adhesion molecule levels, but the increase was more sustained following the high-fat meal. There was no significant change from baseline when vitamin supplementation accompanied each meal. There was a relationship between changes in serum triglycerides and changes in TNF-alpha (r = 0.39, p < 0.01), IL-6 (r = 0.28, p < 0.05) and VCAM-1 (r = 0.25, p < 0.05), and between changes in plasma glucose and changes in IL-6 (r = 0.36, p < 0.01) and ICAM-1 (r = 0.31, p < 0.02). CONCLUSIONS An oxidative mechanism mediates endothelial activation induced by post-meal hyperlipidemia and hyperglycemia.

Regression of Carotid Atherosclerosis by Control of Postprandial Hyperglycemia in Type 2 Diabetes Mellitus

Background—Postprandial hyperglycemia may be a risk factor for cardiovascular disease. We compared the effects of two insulin secretagogues, repaglinide and glyburide, known to have different efficacy on postprandial hyperglycemia, on carotid intima-media thickness (CIMT) and markers of systemic vascular inflammation in type 2 diabetic patients. Methods and Results—We performed a randomized, single-blind trial on 175 drug-naive patients with type 2 diabetes mellitus (93 men and 82 women), 35 to 70 years of age, selected from a population of 401 patients who participated in an epidemiological analysis assessing the relation of postprandial hyperglycemia to surrogate measures of atherosclerosis. Eighty-eight patients were randomly assigned to receive repaglinide and 87 patients to glyburide, with a titration period of 6 to 8 weeks for optimization of drug dosage and a subsequent 12-month treatment period. The effects of repaglinide (1.5 to 12 mg/d) and glyburide (5 to 20 mg/d) on CIMT were compared by using blinded, serial assessments of the far wall. After 12 months, postprandial glucose peak was 148±28 mg/dL in the repaglinide group and 180±32 mg/dL in the glyburide group (P <0.01). HbA1c showed a similar decrease in both groups (−0.9%). CIMT regression, defined as a decrease of >0.020 mm, was observed in 52% of diabetics receiving repaglinide and in 18% of those receiving glyburide (P <0.01). Interleukin-6 (P =0.04) and C-reactive protein (P =0.02) decreased more in the repaglinide group than in the glyburide group. The reduction in CIMT was associated with changes in postprandial but not fasting hyperglycemia. Conclusions—Reduction of postprandial hyperglycemia in type 2 diabetic patients is associated with CIMT regression.

Vascular Effects of Acute Hyperglycemia in Humans Are Reversed by l-Arginine Evidence for Reduced Availability of Nitric Oxide During Hyperglycemia

BACKGROUND Acute hyperglycemia may increase vascular tone in normal humans via a glutathione-sensitive, presumably free radical-mediated pathway. The objective of this study was to investigate whether or not the vascular effects of hyperglycemia are related to reduced availability of nitric oxide. METHODS AND RESULTS Acute hyperglycemia (15 mmol/L, 270 mg/dL) was induced in 12 healthy subjects with an artificial pancreas. Systolic and diastolic blood pressures, heart rate, and plasma catecholamines showed significant increases (P < .05) starting after 30 minutes of hyperglycemia; leg blood flow decreased significantly (15%; P < .05) at 60 and 90 minutes. Platelet aggregation to ADP and blood viscosity also showed significant increments (P < .05). The infusion of L-arginine (n = 7, 1 g/min) but not D-arginine (n = 5, 1 g/min) or L-lysine (n = 5, 1 g/min) in the last 30 minutes of the hyperglycemic clamp completely reversed all hemodynamic and rheological changes brought about by hyperglycemia. Infusion of NG-monomethyl-L-arginine (L-NMMA; 2 mg/min) to inhibit endogenous nitric oxide synthesis in 8 normal subjects produced vascular effects qualitatively similar to those of hyperglycemia but quantitatively higher (P < .05); however, heart rate and plasma catecholamine levels decreased during L-NMMA infusion, presumably as a consequence of baroreflex activation. Infusion of L-NMMA during hyperglycemia produced changes not different from those obtained during infusion of L-NMMA alone. CONCLUSIONS The results show that acute hyperglycemia in normal subjects causes significant hemodynamic and rheological changes that are reversed by L-arginine. Moreover, the effects of hyperglycemia are mimicked to a large extent, but not entirely, by infusion of L-NMMA. This suggests that hyperglycemia may reduce nitric oxide availability in humans.

Metabolic and Cardiovascular Effects of Carvedilol and Atenolol in Non-Insulin-Dependent Diabetes Mellitus and Hypertension: A Randomized, Controlled Trial

Compared with the general population, diabetic patients have an approximately twofold increased risk for hypertension and are more susceptible to the vascular consequences of high blood pressure. Indeed, an estimated 35% to 75% of cardiovascular and renal complications in diabetic patients can be attributed to hypertension [1]. Treatment with -adrenergic antagonists has been shown to be associated with an increased risk for impaired glucose tolerance or diabetes; this has been attributed to the worsening of insulin resistance and the deterioration of lipoprotein metabolism caused by the agents [2]. All this has made physicians reluctant to prescribe -blockers for diabetic patients with hypertension, although cardioselective -blockers have reduced mortality associated with cardiovascular causes in secondary prevention trials [3]. Carvedilol is a multiple-action antihypertensive drug with nonselective -adrenoreceptor and selective -adrenoreceptor blocking activity [4]. Its ratio of 1-blocking potency to 1-blocking potency is 7.6:1 for a 50-mg dose [5]. In addition, carvedilol prevents lipid peroxidation and the depletion of endogenous antioxidants [6]. This may be particularly useful in diabetic patients who may have increased free-radical activity (oxidative stress) [7]. We compared the metabolic and cardiovascular effects of carvedilol with those of atenolol in diabetic patients with hypertension in a randomized, double-blind, controlled trial. Methods Participants Our research protocol was approved by our institutional review board, and informed consent was obtained from patients before participation. Men and women who had noninsulin-dependent diabetes mellitus and had a supine diastolic blood pressure of 90 to 105 mm Hg on at least two occasions at the end of a 4- to 6-week placebo run-in period were eligible to participate. All patients were referred from the outpatient department of our institution and were consecutively chosen. A total of 45 patients met the inclusion criteria and were randomly assigned to treatment. All but 3 patients completed the study. Study Design Our study had a randomized, double-blind design for parallel study groups. Patients who had blood pressure greater than 160/90 mm Hg or who were taking antihypertensive drugs entered a 4- to 6-week run-in period, during which placebo was given to replace the previous antihypertensive drug, if any. Routine hematologic and blood chemistry analyses (hematologic indices, serum sodium and potassium concentrations, liver enzyme levels, urea concentrations, and creatinine concentrations) were done during the initial screening and after the treatment period. Patients were randomly assigned to receive either carvedilol (25 mg once daily) or atenolol (50 mg once daily) in the morning for 24 weeks. After 4 weeks, patients whose diastolic blood pressure while seated was more than 90 mm Hg and had not decreased by at least 10 mm Hg had their dose of study medication doubled for the remaining 20 weeks of the study. A person who was not involved in trial management randomly assigned the patients using random numbers derived from published tables. The list of randomization numbers was used to label the drug boxes, which were given to the participants sequentially. Both patients and caregivers were blinded to treatment, and randomization codes were not broken until all laboratory measurements had been done. Cardiovascular and metabolic variables were checked at the end of the placebo period and at the end of the active treatment period. All participants were instructed to follow a weight-maintaining diet (50% carbohydrates, 30% lipids, 20% protein) for 3 days before the experiments were done. Side effects, concomitant diseases, and blood pressure were assessed by interview and physical examination every fourth week during treatment. Clinical and Laboratory Measurements Patients were asked to refrain from smoking and to fast overnight before each metabolic assessment was done. The euglycemic clamp technique was used to estimate insulin sensitivity in vivo by infusing insulin (1 mU/kg of body weight per minute) and glucose to keep plasma glucose levels at the baseline concentration [8]. At the unchanged plasma glucose concentrations, the amount of glucose required to maintain euglycemia equals whole-body glucose disposal and is expressed in mol/kg per minute (M). The insulin sensitivity index (M/insulin level during the clamp procedure) measures how effectively plasma insulin induces glucose uptake in insulin-sensitive tissues, such as muscle and fat. Substrate oxidation was estimated by indirect calorimetry [9]. On the day after calorimetry, the patients had an oral glucose tolerance test (75 g of glucose). On the third day, they had an insulin tolerance test (0.15 U/kg). Blood pressure was measured with appropriate cuff size three times after patients rested for 5 minutes in the supine position. Plasma glucose, insulin, glucagon, and epinephrine levels were measured as described elsewhere [10]; hemoglobin A1c (HbA1c) was measured by column chromatography (Bio-Rad, Milan, Italy); and cholesterol, triglyceride, and high-density lipoprotein cholesterol levels were determined enzymatically [9]. Left ventricular mass normalized by surface area was measured by echocardiography [9]. Serum levels of lipid peroxides were measured as reaction products of malondialdehyde with thiobarbituric acid (thiobarbituric-acid-reactive substances) according to the method of Waravdekar and Sadlaw [11], with slight modifications. Normal lipid peroxide values for our laboratory are 0.34 to 0.86 mol/L. Statistical Analysis All values in the tables are presented as the mean SD unless otherwise noted; 95% CIs are provided where appropriate. The areas under the glucose and insulin curves were calculated by trapezoidal rule [12]. Change was calculated as the value obtained at the end of intervention minus the value obtained at the beginning of intervention. A preliminary analysis of variance was used to assess the significance within and between groups. One-sample t-tests were used to compare values obtained before and after carvedilol or atenolol therapy, and two-sample t-tests were used for between-group comparisons. Results Three patients (two in the atenolol group and one in the carvedilol group) were unavailable for follow-up; they refused to complete the study and did not specify a reason. These patients dropped out early (between weeks 4 and 8) after randomization; analysis of the study results did not differ when the analysis was done according to actual treatment or according to intention to treat (we used the latter method). Compliance, determined by tablet count, was 94.5% in the carvedilol group and 95% in the atenolol group. The baseline characteristics of the 45 patients who completed the study are shown in Table 1. The two groups were similar at baseline. Body mass index did not change in either group after treatment. Approximately one third of patients in each group (32% in the carvedilol group and 35% in the atenolol group) required upward dose titration at week 4 because of inadequate response. At the end of treatment, 91% of patients receiving carvedilol and 85% of those receiving atenolol had a diastolic blood pressure while seated of less than 90 mm Hg or had their diastolic blood pressure decreased by more than 10 mm Hg (P > 0.2 for comparison). Average systolic and diastolic blood pressure and left ventricular mass decreased in both groups, but the differences between the groups were small (P > 0.2) (Table 2). The decrease in heart rate was greater in patients receiving atenolol than in those receiving carvedilol (P < 0.005). The decrease in mean triglyceride level was 0.56 mmol/L greater (P < 0.001) and the increase in high-density lipoprotein cholesterol level was 0.13 mmol/L greater (P < 0.001) with carvedilol than with atenolol. Table 1. Baseline Characteristics of the Study Patients Table 2. Effects of 24-Week Intervention with Carvedilol or Atenolol in 45 Patients with Non-Insulin-Dependent Diabetes Mellitus and Hypertension* Mean fasting plasma glucose and insulin levels decreased during carvedilol treatment and increased during atenolol treatment (Table 2). The HbA1c level decreased by 1.4% in the carvedilol group and increased by 4% in the atenolol group (P < 0.001 for the difference). Mean total glucose disposal and insulin sensitivity index increased during carvedilol treatment and decreased during atenolol treatment (P 0.01 for the difference). Serum levels of thiobarbituric-acid-reactive substances decreased by 0.25 mol/L in the carvedilol group and did not change in the atenolol group (P < 0.001 for the difference). The decreases in plasma glucose and insulin responses to the oral glucose load were 61 mmol/L 180 minutes greater (CI, 101 to 21 mmol/L 180 minutes; P = 0.035) and 6.2 nmol/L 180 minutes greater (CI, 9.8 to 2.6 nmol/L 180 minutes; P = 0.03), respectively, with carvedilol than with atenolol (data not shown). The plasma glucose level nadir occurred 60 minutes after the insulin bolus was administered and was not affected by either drug (P = 0.09) (data not shown). Glucagon and epinephrine responses to hypoglycemia were similar before and after treatment with both drugs (P > 0.08) (data not shown). Discussion Our results show that both carvedilol and atenolol effectively decrease blood pressure and ventricular mass in patients with diabetes and hypertension. They also show that the drug doses administered in this study are equivalent with regard to their ability to decrease blood pressure in these patients, who are particularly at risk for cardiovascular disease. The similarities between the two drugs end with their cardiovascular effects, however; their metabolic effects are different and, to a large extent, divergent. Fasting plasma glucose and insulin levels decreased during carvedilol treatment and increased during atenolol treatment. Th

Acute hyperglycemia induces an oxidative stress in healthy subjects

Recent prospective studies indicate that long-term glycemic control of diabetes is an important predictor not only of microvascular disease but also of macrovascular complications, including coronary heart disease (1). Possible links between glucose and cardiovascular events in the diabetic patient include modifications of important vascular functions of the endothelium with a switch from a quiescent, relaxant, antithrombotic, antioxidant, and antiadhesive state to an activated state displaying a more atherogenetic risk profile (2). Generation of reactive oxygen species could be a common downstream mechanism by means of which multiple byproducts of glucose are exerting their adverse effects on blood vessels (3). Indeed, in April 2001, Pennathur et al. (4) reported in the JCI that hyperglycemia favors oxidative reactions in the microenvironment of the artery wall in vivo. We studied the effect of acute elevations of plasma glucose levels on plasma nitrotyrosine, a marker of oxidative stress, in 20 healthy subjects (11 men, 9 women). Their age was 34 ± 4 years (mean ± SD), and the body mass index was 24 ± 1 kg/m2. None used any medication. After giving informed written consent to participate in the study, each subject underwent a hyperglycemic glucose clamp test in which plasma glucose concentrations were acutely raised at about 15 mmol/l for 120 minutes (Figure ​(Figure1).1). Mean blood pressure and nitrotyrosine (5) rose significantly during the clamp; there was a positive correlation (r = 0.49) between nitrotyrosine and mean blood pressure increases during hyperglycemia. In control studies (n = 6), in which plasma glucose was maintained at normal concentrations (5 mmol/l for 120 minutes), we could detect no variation in nitrotyrosine plasma levels from baseline (baseline: 0.15 ± 0.05 μmol/l; 120-minute values: 0.13 ± 0.05 μmol/l, P = not significant). Figure 1 Twenty healthy subjects were submitted to a hyperglycemic glucose clamp study in which plasma glucose levels were acutely raised to 15 mmol/l (0.33 g/kg as intravenous bolus injection followed by a variable 30% glucose infusion). Mean blood pressure ... We show here that acute hyperglycemia in normal subjects causes an oxidative stress as evidenced by the raised circulating nitrotyrosine levels during the hyperglycemic clamp. However, we cannot exclude the possibility that some nitrotyrosine can be generated via a peroxynitrite-independent mechanism, or that a reduced nitrotyrosine clearance during hyperglycemia could also contribute to its raised plasma concentrations. Since nitrotyrosine is considered a good marker of peroxynitrite formation (6), and since peroxynitrite may account for a considerable portion of the toxic effects previously attributed to nitric oxide or the superoxide anion (7), it is possible that some of the toxic effects of hyperglycemia on the vascular tree may be modulated by peroxynitrite. Acute hyperglycemia in normal subjects may in fact induce vasoconstriction, activate thrombosis, increase the circulating levels of soluble adhesion molecules, and prolong the QT interval (8, 9). The recent demonstration (10) that apoptosis of myocytes, endothelial cells, and fibroblasts in heart biopsies taken from diabetic patients is selectively associated with intracellular levels of nitrotyrosine supports a role for high-energy oxidants (such as peroxynitrite) as mediators of the vascular damage brought about by hyperglycemia.

Metformin Improves Glucose, Lipid Metabolism, and Reduces Blood Pressure in Hypertensive, Obese Women

OBJECTIVE To determine the effects of metformin on blood pressure, left ventricular mass, and some metabolic and endocrine parameters in nondiabetic, obese, hypertensive women. RESEARCH DESIGN AND METHODS Twelve obese, nondiabetic, hypertensive women received 850 mg metformin 2 times/day for 12 wk and placebo for another 12 wk, according to a double-blind, cross-over, randomized design. All patients were hospitalized 4 times, i.e., before randomization and after each treatment (metformin or placebo), to conduct metabolic and cardiovascular investigations (oral glucose tolerance test, euglycemic clamp associated with indirect calorimetry, and echocardiography). RESULTS Fasting glucose, HbA1c, fasting and glucose-stimulated insulin, blood pressure and left ventricular mass, cholesterol, triglycerides, and fibrinogen decreased significantly after metformin treatment, whereas high-density lipoprotein cholesterol increased. The improvement in glucose metabolism resulted from increased sensitivity to insulin. CONCLUSIONS These findings suggest that metformin treatment in obese, nondiabetic, hypertensive women produces a more favorable cardiovascular risk profile.

Circulating Adhesion Molecules in Humans Role of Hyperglycemia and Hyperinsulinemia

BACKGROUND We assessed the role of glucose and insulin in the regulation of circulating levels of soluble intercellular adhesion molecule-1 (sICAM-1) and vascular adhesion molecule-1 (sVCAM-1) in normal subjects and in patients with type 2 diabetes. METHODS AND RESULTS Plasma glucose concentrations were acutely raised in 10 normal subjects and 10 newly diagnosed, complication-free type 2 diabetic patients and maintained at 15 mmol/L for 2 hours. In normal subjects, plasma sICAM-1, but not sVCAM-1, levels rose significantly (P<0.01) at 1 hour and returned to basal values at 2 hours. In another study, octreotide was infused during the hyperglycemic clamp to block the release of endogenous insulin; this prevented the late fall of plasma sICAM-l levels observed in under control clamp conditions. The diabetic patients had plasma sICAM-1 levels significantly higher (P<0.01) than those of the control subjects; plasma sVCAM-1 levels were similar. Both sICAM-l and sVCAM-1 concentrations did not change significantly during the control hyperglycemic clamp; however, octreotide infusion increased plasma sICAM-1 levels, which remained significantly (P<0.05) above baseline during the whole clamp. In an additional 10 type 2 diabetic patients, overnight euglycemia (plasma glucose 5.5 mmol/L) obtained with the aid of an artificial pancreas or supplementation with l-arginine (10 g PO for 30 days), the natural precursor of NO, normalized the increased plasma sICAM-1 levels. CONCLUSIONS Acute hyperglycemia increases circulating sICAM-1 levels in normal subjects, whereas the correction of hyperglycemia with insulin or l-arginine supplementation restored to normal levels the increased plasma sICAM-1 levels of type 2 diabetic patients.

Reduction of Oxidative Stress and Inflammation by Blunting Daily Acute Glucose Fluctuations in Patients With Type 2 Diabetes: Role of dipeptidyl peptidase-IV inhibition

OBJECTIVE Evaluate the effects of two dipeptidyl peptidase-IV (DPP-4) inhibitors, sitagliptin and vildagliptin, known to have different efficacy on mean amplitude of glycemic excursions (MAGE), on oxidative stress, and on systemic inflammatory markers in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS A prospective, randomized, open-label PROBE design (parallel group with a blinded end point) study was performed in 90 patients with type 2 diabetes inadequately controlled by metformin. The study assigned 45 patients to receive sitagliptin (100 mg once daily; sitagliptin group) and 45 patients to receive vildagliptin (50 mg twice daily; vildagliptin group) for 12 weeks. MAGE, evaluated during 48 h of continuous subcutaneous glucose monitoring, allowed an assessment of daily glucose fluctuations at baseline and after 12 weeks in all patients. Assessment of oxidative stress (nitrotyrosine) and systemic levels of inflammatory markers interleukin (IL)-6 and IL-18 was performed at baseline and after 12 weeks in all patients. RESULTS HbA1c, fasting and postprandial glucose, MAGE, and inflammatory and oxidative stress markers were similar between the groups at baseline. After 12 weeks, MAGE (P < 0.01) was lower in the vildagliptin group than in the sitagliptin group. After treatment, HbA1c and postprandial glucose evidenced similar changes between the groups (P = NS). Vildagliptin treatment was associated with a stronger decrease in nitrotyrosine (P < 0.01), IL-6 (P < 0.05), and IL-18 (P < 0.05) than sitagliptin treatment. Nitrotyrosine and IL-6 changes significantly correlated with changes in MAGE but not in fasting glucose and HbA1c. CONCLUSIONS MAGE reduction is associated with reduction of oxidative stress and markers of systemic inflammation in type 2 diabetic patients. These effects were greater in the vildagliptin group than in the sitagliptin group.

The vascular effects of L-Arginine in humans. The role of endogenous insulin.

This study aimed at evaluating whether increased availability of the natural precursor of nitric oxide, L-arginine, could influence systemic hemodynamic and rheologic parameters in humans and whether the effects of L-arginine are mediated by endogenous insulin. 10 healthy young subjects participated in the following studies: study I, infusion of L-arginine (1 g/min for 30 min); study II, infusion of L-arginine plus octreotide (25 microg as i.v. bolus + 0.5 microg/min) to block endogenous insulin and glucagon secretion, plus replacement of basal insulin and glucagon; study III, infusion of L-arginine plus octreotide plus basal glucagon plus an insulin infusion designed to mimic the insulin response of study I. L-Arginine infusion significantly reduced systolic (11+/-3, mean+/-SE) and diastolic (8+/-2 mmHg, P < 0.001) blood pressure, platelet aggregation (20+/-4%), and blood viscosity (1.6+/-0.2 centipois, P < 0.01), and increased leg blood flow (97+/-16 ml/min), heart rate, and plasma catecholamine levels (P < 0.01). In study II, plasma insulin levels remained suppressed at baseline; in this condition, the vascular responses to L-arginine were significantly reduced, except for plasma catecholamines which did not change significantly. In study III, the plasma insulin response to L-arginine was reestablished; this was associated with hemodynamic and rheologic changes following L-arginine not significantly different from those recorded in study I. These findings show that systemic infusion of L-arginine in healthy subjects induces vasodilation and inhibits platelet aggregation and blood viscosity. These effects are mediated, in part, by endogenous released insulin.