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.

Metformin improves hemodynamic and rheological responses to L-arginine in NIDDM patients.

OBJECTIVE: The endothelium plays a pivotal role in the regulation of vascular tone by releasing nitric oxide (NO). Increased availability of L-arginine, the natural precursor of NO, induces vasodilatation and inhibits platelet activity. We studied the effect of metformin on hemodynamic and rheological responses to L-arginine in patients with NIDDM. RESEARCH DESIGN AND METHODS: Ten newly diagnosed NIDDM patients with mild fasting hyperglycemia (7.5 +/- 0.3 mmol/l) and without evidence of both micro- and macrovascular complications were investigated. They received an intravenous infusion of L-arginine (1 g/min for 30 min) with evaluation of plasma glucose and insulin, systolic (sBP) and diastolic (dBP) blood pressure, heart rate and plasma catecholamines, platelet aggregation, and blood viscosity and filterability. The L-arginine test was repeated after an 8-week treatment with metformin (850 mg b.i.d.). RESULTS: Metformin treatment significantly reduced basal fasting plasma glucose, HbA1c, and platelet aggregation to ADP (P < 0.05); the other parameters did not change. During pretreatment test, L-arginine infusion decreased sBP (from 137 +/- 4.1 to 129 +/- 4.5 mmHg, P < 0.01) and dBP (from 79 +/- 1.9 to 75 +/- 1.2 mmHg, P < 0.01) without affecting heart rate or plasma catecholamines. Both platelet aggregation and blood viscosity showed significant decrements after L-arginine, while blood filterability did not change. After metformin treatment, the decrease in blood pressure after L-arginine infusion was significantly enhanced, with a maximal decrease of sBP of 12 +/- 3.4 mmHg (8 +/- 2.5 mmHg pretreatment, P < 0.05) and dBP of 9.5 +/- 2.4 mmHg (4.5 +/- 1.9 mmHg pretreatment, P < 0.01). Heart rate, plasma norepinephrine levels, and blood filterability also rose significantly (P < 0.05-0.01). The decrease in both platelet aggregation and blood viscosity after L-arginine was significantly amplified after metformin. CONCLUSIONS: We conclude that L-arginine infusion in newly diagnosed NIDDM patients without vascular complications produces relevant hemodynamic and theological changes, which are amplified by an 8-week treatment with metformin. Whether these vascular effects of metformin will improve the poor cardiovascular outlook of the diabetic patient is still unknown.

Hemorheological and cardiovascular responses to beta-endorphin and naloxone in healthy subjects and in patients with essential hypertension.

The purpose of the present study was to determine if opioid agonism (beta-endorphin) and antagonism (Naloxone) exert rheological and cardiovascular effects in normal humans and in patients with essential hypertension. Eight hypertensive patients were matched for age, sex, and body habitus (body mass index, waist to hip ratio) with eight normotensive healthy subjects. In all subjects, heart rate and blood pressure (continuous automatic recording), blood and plasma viscosity, fibrinogen, hematocrit, and platelet aggregation to ADP were evaluated during an infusion of human synthetic beta-endorphin (0.5 mg/h). On a different day and in randomized order, the subjects were submitted to another beta-endorphin infusion preceded by an i.v. naloxone bolus (5 mg in 5 min). beta-Endorphin and naloxone failed to significantly alter heart rate or blood pressure in both normotensive and hypertensive subjects. In hypertensive patients, beta-endorphin significantly increased blood viscosity and ADP-induced platelet aggregation, but only the former effect was naloxone-sensitive. In normotensive subjects, beta-endorphin caused a transient but significant decrease of platelet aggregation that was reversed by naloxone. These data suggest that beta-endorphin may play some role in the inhibitory control of platelet aggregation in normal subjects. An altered responsiveness of some rheological determinants to beta-endorphin seems to be present in human hypertension.

L-arginine but not D-arginine stimulates insulin-mediated glucose uptake.

Our study aims at investigating a possible role for L-arginine and D-arginine in insulin-mediated glucose uptake. Twelve lean healthy subjects volunteered for the study and were submitted to three euglycemic-hyperinsulinemic glucose clamps to investigate the effect of L-arginine (0.5 g/min in the last 60 minutes of the clamp), D-arginine (0.5 g/min in the last 60 minutes of the clamp), and saline 0.9% NaCl on insulin-mediated glucose uptake. All tests were made in random order. In study 1, L-arginine versus saline infusion was associated with a significant increase in blood flow (131% +/- 7% v 87% +/- 5%, P < .001) and whole-body glucose disposal ([WBGD] 61.4 +/- 4.4 v 41.3 +/- 3.5 mumol/kg fat-free mss [FFM].min, P < .001). Analysis of substrate oxidation demonstrated that both oxidative and nonoxidative glucose metabolism was improved by L-arginine delivery. After adjustment for the change in blood flow, WBGD was still greater after L-arginine than after saline infusion. Along with L-arginine infusion and independently of the change in blood flow, the percent change in WBGD correlated with the percent change in plasma cGMP (r = .55, P < .05). D-Arginine infusion did not affect insulin-mediated glucose uptake. In particular, WBGD (42.1 +/- 3.4 v 41.3 +/- 3.5 mumol/kg FFM.min, P = NS) was similar in both experimental conditions. Basal levels (2.8 +/- 0.2 v 2.7 +/- 0.3 nmol/L, P = NS) and the insulin-mediated increase (43% +/- 5% v 39% +/- 4%, P = NS) in plasma cGMP were also superimposable along with insulin plus D-arginine and insulin alone, respectively. Finally, blood flow (224 +/- 29 v 230 +/- 35 mL/min, P = NS) was not different at baseline and was similarly stimulated (84% +/- 4% v 87% +/- 5%, P = NS) by insulin infusion. In conclusion, L-arginine but not D-arginine stimulates insulin-mediated glucose uptake. Nitric oxide (NO), the metabolic mediator for L-arginine, potentiates insulin-mediated glucose uptake through the increase in blood flow. Nevertheless, an independent effect of intracellular cGMP on WBGD cannot be ruled out.

A 'de novo' arisen case of angioedema C1-inhibitor deficiency dependent: possible mutagenic effect of azathioprine?

It is reported that a C1-inhibitor (CI-INH) deficiency dependent angiodema case arose 'de novo' in a child without a family history of this disease. His mother was undergoing immunosuppressive therapy (50 mg of azathioprine plus 8 mg of methyl-prednisolone daily) during pregnancy, uninterrupted for seven years because of a kidney transplant. All the other known causes of acquired C1-INH deficiency were excluded. An involvement of an azathioprine-induced C1-INH gene mutation is hypothised.

Glutathione (GSH) improved haemostatic and haemorheological parameters in atherosclerotic subjects.

Blood samples from ten patients with clinically evident manifestations of atherosclerotic disease were used to evaluate in vitro the effects of exogenous glutathione (GSH) on platelet aggregation and on blood filtration and viscosity. In two groups, each of ten atherosclerotic patients, matched for sex, age, prevalent localization, duration and gravity of disease, the effects of GSH infusion (600 mg every day for seven days) on the haemocoagulative pattern, platelet aggregation and blood filtration and viscosity were evaluated in a double-blind, placebo cross-over trial. The GSH in vitro addition resulted in a significant increase in blood filtration and a significant decrease in blood viscosity and platelet aggregation. The venous GSH infusion both significantly decreased blood viscosity and increased blood filtration. Partial thromboplastin time was lengthened after GSH infusion even thought it remained in the normal range.

Hemorheological and cardiovascular effects of exercise training in the rehabilitation of elderly patients with chronic obstructive pulmonary disease.

The purpose of this study is to evaluate hemorheological effects of a single exercise respiratory session (SERS), in the rehabilitation of elderly patients with chronic obstructive pulmonary disease (COPD). Fifteen elderly patients with COPD and 15 controls, matched for demographic variables and body habitus, were submitted to a single session of relaxation and unsupported upper-extremity exercise, coordinated with breathing. We measured hemogasanalytical and cardiovascular parameters: hematocrit value, platelet aggregation, beta-TG and PF(4) plasma levels, blood viscosity and erythrocyte filterability. In both groups, SERS significantly decreased platelet aggregation (P<0.05), beta-TG and PF(4) plasma levels (P<0.05). Erythrocyte filterability and diastolic blood pressure showed a trend to increase in both groups but reached a significant difference in patients with COPD only. Respiratory exercise has a positive influence on platelet and hemorheological parameters in the elderly with COPD. The increase of diastolic blood pressure requires active surveillance.

Hyperbaric oxygen, oxygen-ozone therapy, and rheologic parameters of blood in patients with peripheral occlusive arterial disease.

For many years, clinical practice has consolidated the use of both hyperbaric oxygen and oxygen-ozone therapy in the treatment of peripheral occlusive arterial disease (POAD). We investigated the influence of these treatments on hemorrheologic parameters that play an important role in the pathogenesis and the clinical course of arteriosclerosis. Two groups of 15 patients suffering from POAD, assigned at random either to a cycle of HBO therapy or O2-O3 therapy, were evaluated for blood viscosity, erythrocyte filterability, hematocrit value, fibrinogen concentration, and thrombin time. The O2-O3 therapy caused a significant increase of erythrocyte filterability and a significant decrease of blood viscosity. By contrast, HBO therapy did not produce any significant change. The increase of lipid peri-oxidation, proved by raised malonyldialdehyde plasma levels, seems a likely mechanism involved in the hemorrheologic effects of O2-O3 therapy.

Air pollution by gasoline exhaust fumes: effect on platelet function and blood viscosity.

Air pollution induced by automobile exhaust fumes seems to be involved in increased cardiovascular and respiratory morbidity. The effects of inhalation of such pollutant gases on platelet function and blood viscosity have not been sufficiently investigated, even if these parameters seem to be in strict correlation with cardiovascular function. Twelve healthy non-smoking volunteers were exposed for 30 minutes in a closed room to air polluted by automobile fumes. Platelet aggregation, blood viscosity, HbCO levels and P50 STD were determined before and after exposure. Cardiovascular parameters (blood pressure, heart rate and ECG) were also measured. At the end of the test, HbCO levels were significantly increased, but P50 STD was significantly reduced; an impairment of both platelet function and blood viscosity was observed. No significant changes in cardiovascular parameters were recorded. The decreases in platelet aggregation and blood viscosity were not directly correlated with either the increase in carbon monoxide levels or with the reduced P50 STD levels. It can be reasonably concluded that gasoline exhaust fumes could have been responsible for the observed alterations.

Influence of ozone on haemoglobin oxygen affinity in type-2 diabetic patients with peripheral vascular disease: in vitro studies.

The use of ozone in the treatment of peripheral vascular disease (PVD) is increasing. The purpose of this study was to evaluate the effect of ozone on haemoglobin oxygen affinity in Type-2 diabetic patients with PVD. Twenty diabetic patients presenting with PVD (Clinical stage II-IV according to Fontaine) and 20 non-diabetic healthy matched subjects were studied. In both groups, aliquots of blood were ozonised with mixtures of oxygen-ozone (O2-O3) to reach end-concentrations of 6.5, 13, 26 and 78 micrograms O3 per ml of substrate. At baseline, diabetic patients presented significantly lower haemoglobin oxygen affinity values but higher plasma levels of free haemoglobin and malonyldialdehyde (MDA) than controls. In both diabetic patients and controls, exposure of blood to ozone reduced haemoglobin oxygen affinity in an "all-or-none" fashion, without changing 2-3, diphosphoglycerate concentrations in erythrocytes. Both free haemoglobin and MDA concentrations showed significant, dose-dependent increases after blood ozonisation. Thus, ozone caused a significant increase in oxygen unloading of haemoglobin in both normal subjects and Type-2 diabetic patients with PVD.

[Effects of low O2 tension on platelet aggregation]. / Effetti della bassa tensione di O2 sull'aggregabilita' piastrinica.

Several studies in animals suggest a link between haemocoagulative patterns and blood gas changes. Furthermore platelet functions seem to be affected by O2 concentrations. In the present study we have evaluated "in vitro" the effect of low PO2 concentrations on platelet aggregation in man. In 15 normal subjects (mean age 32 +/- 5) platelet aggregation ADP (end conc. 1,25 microM) and collagen induced 2 micrograms/Ml) was determined before and after exposition to low PO2 concentrations (O2 conc. 5,04%). The results show that low PO2 concentrations determine a significant increase (P less than 0,001) of platelet aggregation as compared to controls. Although the mechanism of the direct influence of PO2 concentrations upon human platelet is unclear, this finding suggest new therapeutic approaches in chronic lung obstructive diseases.

L-arginine for testing endothelium-dependent vascular functions in health and disease.

The objective of this study was to assess the role of L-arginine, the natural precursor of nitric oxide, for testing endothelial function in physiological and pathophysiological conditions. In an initial study of 20 healthy subjects, mean blood pressure decreases in response to increasing doses of L-arginine (1, 2, 3, and 5 g) were 1.1 +/- 1.3, 2.6 +/- 1.5, 7.6 +/- 1.3, and 7.7 +/- 2 mmHg, respectively, P < 0.01. The enantiomer D-arginine (3 g) did not produce any change in mean blood pressure and platelet aggregation (n = 10), whereas the infusion of the L-arginine analog NG-monomethyl-L-arginine (6 mg/min) reduced by 70% the vascular effects of L-arginine. In the whole population of 52 healthy subjects, there was an inverse correlation between age and blood pressure or platelet aggregation changes after L-arginine. Compared with matched controls (n = 20), the changes in mean blood pressure and platelet aggregation after L-arginine were significantly lower in non-insulin-dependent diabetic (n = 20) and hypercholesterolemic (n = 16), but not in hypertensive (n = 20), subjects. Changes in blood viscosity were significantly lower only in hypercholesterolemic subjects. Our findings suggest that an intravenous bolus of 3 g L-arginine may be a simple and useful tool to assess the endothelial control of blood pressure and platelet activity in health and disease.

Abnormal rheologic effects of glyceryl trinitrate in patients with non-insulin-dependent diabetes mellitus and reversal by antioxidants.

OBJECTIVE: To evaluate 1) the hemorrheologic and hemodynamic effects of glyceryl trinitrate in patients with non-insulin-dependent diabetes mellitus and 2) the influence of antioxidants on these effects. DESIGN: Case-control study. SETTING: University hospital clinic. PATIENTS: 40 patients with diabetes and no evidence of cardiovascular complications and 40 controls matched for demographic variables and body habitus. INTERVENTIONS: Sublingual glyceryl trinitrate (0.3 mg) and transdermal glyceryl trinitrate patches (10 mg/d). Vitamin E, 300 mg/d orally for 7 days, and glutathione, 600 mg intravenously or intramuscularly, were given to test the effects of antioxidant supplementation. MEASUREMENTS: Systolic, diastolic, and mean arterial pressure and heart rate; left ventricular ejection fraction; platelet aggregation, blood viscosity, and blood filterability in vitro and ex vivo. RESULTS: Compared with controls, patients with diabetes had increased platelet aggregation to adenosine diphosphate (P < 0.005), increased blood viscosity (P < 0.001), and decreased blood filterability (P = 0.041) at baseline; blood pressure, heart rate, and ejection fraction were similar in the two groups. In controls, both sublingual glyceryl trinitrate and transdermal glyceryl trinitrate patches significantly reduced platelet aggregation (-38%; 95% CI, -49% to -27%) and blood viscosity (-8%; CI, -11% to -5%) and increased blood filterability (10%; CI, 7.0% to 13.1%). Slight but significant decreases in blood pressure and ejection fraction and an increase in heart rate were also seen in controls after administration of glyceryl trinitrate (both preparations). In patients with diabetes, glyceryl trinitrate paradoxically increased platelet aggregation (24%; CI, 15% to 33%) and blood viscosity (6%; CI, 2.9% to 8.8%) and decreased blood filterability (-7%; CI, -9.5% to -4.4%); hemodynamic values did not change significantly. In both groups, rheologic responses to glyceryl trinitrate (end concentration, 100 and 200 ng/mL) in vitro were similar to those seen in ex vivo studies. Vitamin E and glutathione normalized rheologic responses to glyceryl trinitrate in patients with diabetes. CONCLUSIONS: Organic nitrates have beneficial effects on blood rheology in controls but not in patients with diabetes, in whom a paradoxical deterioration is seen. Antioxidant supplementation can normalize primary tolerance to the rheologic effects of nitrates in diabetes.

Effect of insulin on blood rheology in non-diabetic subjects and in patients with Type 2 diabetes mellitus.

We evaluated the effect of insulin on platelet function, blood viscosity, and filterability in healthy subjects and in patients with Type 2 (non-insulin-dependent) diabetes mellitus. Fifteen diabetic patients were free from cardiovascular complications (group A), while the other 15 patients had both clinical and measured evidence of coronary or peripheral vascular disease (group B); 15 non-diabetic subjects served as controls. On blood samples taken without stasis, maximal platelet aggregation to 1.25 micromol l(-1) ADP, blood and plasma viscosity, and blood filterability were measured in basal conditions, and after incubation of blood, plasma or platelet-rich plasma with insulin at two physiological concentrations (120 and 480 pmol l(-1)). Compared with healthy subjects, the diabetic patients of group B had higher values of blood (p < 0.01) and plasma (p < 0.05) viscosity, and platelet aggregation response to ADP (p < 0.01), as well as lower values of blood filterability (p < 0.01). The diabetic patients of group A had values intermediate between normal subjects and the patients of group B. In non-diabetic subjects, insulin significantly decreased platelet aggregation and blood viscosity at low shear rates (22.5 s(-1)) (p < 0.01 for both), and had no significant effects on other parameters. In the diabetic patients of group A, insulin decreased blood viscosity at high (225 s(-1)) rates of shear (p < 0.01) and increased blood filterability (p < 0.01). The effects of insulin were not dose-related. In the diabetic patients of group B, none of the parameters evaluated was significantly influenced by insulin. Type 2 diabetic patients present many abnormalities of the rheologic properties of blood. The beneficial effects of insulin on platelet aggregation and blood viscosity are not evident in Type 2 diabetic patients, especially those with vascular complications and this may be relevant to the development of those complications.

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.

Glutathione reverses systemic hemodynamic changes induced by acute hyperglycemia in healthy subjects.

The present study aimed at evaluating whether acute elevations of plasma glucose concentrations could influence systemic hemodynamic parameters and baroreflex activity in humans. Plasma glucose concentrations were acutely raised to 15 mmol/l in 12 healthy male volunteers. During hyperglycemia, there were significant increments of systolic [from 118 +/- 9 to 138 +/- 12 (SD) mmHg, P < 0.01] and diastolic (from 71 +/- 5 to 85 +/- 6 mmHg, P < 0.001) blood pressure, as well as heart rate (from 76 +/- 7 to 85 +/- 10 beats/min, P < 0.01) and plasma catecholamine levels. Both maximal and steady-state mean arterial pressure after squatting were higher during hyperglycemia (27 +/- 8 and 16 +/- 6 mmHg, respectively) compared with levels obtained during euglycemia (18 +/- 5 and 2 +/- 0.6 mmHg, respectively, P < 0.001). The infusion of the somatostatin analogue octreotide (25 micrograms as i.v. bolus followed by a 0.5 microgram/min infusion), to avoid the possible confounding vascular actions of insulin, did not influence the hemodynamic effects of hyperglycemia except for a lesser increase of both heart rate and plasma catecholamines. Glutathione (600 mg as an iv bolus followed by a 5 mg/min infusion) completely prevented the vascular effects of hyperglycemia. This study shows that acute hyperglycemia, similar to that observed in poorly controlled diabetic patients, produces relevant systemic hemodynamic changes and also alters baroreflex activity via a glutathione-sensitive presumably free radical-mediated pathway.