Role of free fatty acids on cardiac autonomic nervous system in noninsulin-dependent diabetic patients: effects of metabolic control

Decreased heart rate variability (HRV) is a risk factor for cardiovascular mortality. Elevated plasma free fatty acid (FFA) levels decrease HRV in healthy subjects. Thus, we investigated the effect of changes in plasma FFA levels on HRV, in non-insulin-dependent diabetes (NIDDM) patients. Thirty NIDDM patients free from diabetic neuropathy volunteered for a study made by two phases. In study A, changes in HRV along a 10% lipid emulsion infusion + heparin (n = 15) or saline infusion (control study; n = 15) were investigated. In study B, all patients (n = 30) underwent further determination of HRV after 3 months of improved metabolic control achieved by intensified insulin treatment. In study A, lipid emulsion infusion increased plasma FFA (P < 0.001) and catecholamine concentrations (P < 0.005), mean arterial blood pressure (P < 0.005), low frequency/high frequency (LF/HF) ratio (P < 0.001). Delta plasma FFA levels correlated with delta LF/HF ratio (r = 0.57; P < 0.02). Along with saline infusion, metabolic and cardiovascular parameters remained unchanged throughout the test. In study B, improved metabolic control lowered fasting plasma glucose (P < 0.005), FFA (P < 0.001), norepinephrine (P < 0.02), epinephrine (P < 0.04), and glycosylated hemoglobin levels (P < 0.001), mean arterial blood pressure(P < 0.05), and LF/HF ratio (P < 0.001). Again percent decline in plasma FFA correlated with the percent change in LF/HF ratio (r = 0.72; P < 0.001). In a multivariate analysis, percent changes in LF/HF ratio were associated with percent changes in plasma FFA independently of gender and percent changes in body mass index, waist/hip ratio, plasma norepinephrine, epinephrine, glycosylated hemoglobin, and daily insulin therapy. Our study demonstrates that changes in plasma FFA levels may have a parallel effect on cardiac sympathetic/parasympathetic nervous system balance in NIDDM patients.

High glucose induces ventricular instability and increases vasomotor tone in rats

AIMS/HYPOTHESIS

To investigate cardiac repolarization time in streptozotocin-induced diabetic rats and isolated hearts perfused with high glucose concentration.

METHODS

We studied the effects of streptozotocin-induced diabetes on the cardiac repolarisation time (Q-T interval) in Sprague-Dawley rats during a 4-day period of hyperglycaemia and a subsequent 4-day period of normoglycaemia. The Q-T interval was also evaluated in isolated hearts of non-diabetic rats, in condition of high glucose concentration.

RESULTS

Hyperglycaemia in streptozotocin rats increased mean blood pressure and led to a significant (p < 0.001) prolongation of Q-T values, which normalized after 4 days of normoglycaemia with intravenous insulin infusion. Perfusion of isolated hearts in condition of high glucose concentration caused a significant prolongation of Q-T values and increased coronary perfusion pressure (p < 0.001). The effects of high glucose were completely prevented by glutathione and almost completely by L-arginine, the natural precursor of nitric oxide. In a condition of normal glucose, L-NAME, an inhibitor of endogenous nitric oxide synthesis, increased both Q-T and CPP values to levels similar to those induced by high glucose (p < 0.001). Verapamil completely prevented Q-T lengthening and reduced by about two-thirds CPP values (p < 0.001).

CONCLUSION/INTERPRETATION

Streptozotocin-diabetes in rats produces significant haemodynamic and electric perturbations that are reversed by normoglycaemia. Moreover, high glucose increases Q-T and CPP values in the isolated hearts of non-diabetic rats. The latter effects are reversed by glutathione and L-arginine, partially reversed by verapamil and mimicked by L-NAME. By increasing the production of free radicals, high glucose could reduce nitric oxide availability to target cells inducing a state of increased vasomotor tone and ventricular instability.

Hyperglycemia and QT interval: time for re-evaluation

Among the many mechanisms proposed to explain the relationship between glucose levels and subsequent cardiovascular events, a prolonged QT interval, ie the time interval between the start of activation of the ventricle and completion of its repolarization, seems noteworthy. In Type 2 diabetic patients, for example, the prevalence of QTc (corrected QT interval) prolongation is as high as 26% and is associated with heart disease. The mechanism by which hyperglycemia may produce ventricular instability, as manifested in QTc prolongation, may be increased sympathetic activity, increased cytosolic calcium content in myocytes, or both. By raising the production of free radicals, high glucose may reduce nitric oxide (NO) availability to target cells inducing a state of increased vasomotor tone and ventricular instability. Reduction of Na+/K+-ATPase activity, inhibition of Ca2+-ATPase activity, depressed Na+/Ca2+ exchanger activity, and activation of Na+/H+ antiport may all be implicated. Further studies are urgently needed to characterize in full the effect of hyperglycemia on vascular cells, in order to find therapeutic approaches that lessen the burden of cardiovascular morbidity and mortality in human diabetes.

The BB-paraoxonase genotype is associated with impaired brachial reactivity after acute hypertriglyceridemia in healthy subjects

The possible relationship between paraoxonase (PON) gene polymorphism and brachial reactivity in healthy adult subjects in the presence of acute hypertriglyceridemia (HT), as a prooxidant factor, was investigated. In 101 healthy subjects the response to flow- induced vasodilatation was measured before and after Intralipid infusion. In the same subjects the A/B PON polymorphism was detected. The frequency was 0.545 for AA genotype, 0.356 for the AB genotype, and 0.099 for the BB genotype. At baseline all genotype groups had a similar increase in brachial artery diameter and flow. After Intralipid infusion, subjects sharing the BB genotype had a significant decrease vs. baseline values in changes in brachial artery diameter (P for trend < 0.001 vs. the other genotypes), but not in flow. In a subgroup of 55 subjects distributed among the 3 PON genotypes the same study protocol was repeated by buccal nitroglycerine administration to study the endothelium-independent vasodilatation. Again, subjects with the BB genotype had the worse vasodilation (P for trend < 0.001). Furthermore, subjects sharing the BB genotype had the lowest endothelium-independent and -dependent changes in diameter (P for trend < 0.001 vs. the other genotypes) independently of gender ratio, basal plasma triglycerides concentrations, and changes in plasma triglycerides concentrations. In conclusion, our study demonstrates that transient HT decreases vascular reactivity more in subjects with the PON BB genotype than in those with the other PON genotypes.

Plasma leptin concentration, insulin sensitivity, and 24-hour ambulatory blood pressure and left ventricular geometry

Left ventricular (LV) hypertrophy is an important predictor of cardiovascular morbidity and mortality. Hemodynamic factors, such as 24-h blood pressure (BP) values, are responsible for left ventricular hypertrophy in hypertensives. On the other hand, some metabolic factors have also been suggested to affect LV mass and geometry. In particular, plasma leptin concentrations have been found associated to LV myocardial growth. Because chronic leptin infusion stimulates sympathetic nervous system activity and increases BP levels, the role of 24-h BP values on leptin-related changes in myocardial wall geometry cannot be ruled out. Thus, the aim of our study was to evaluate whether the relationship between plasma leptin levels and LV wall thickness is mediated by 24-h BP values in hypertensive male patients. Thirty-six newly diagnosed hypertensive patients underwent Doppler echocardiographic examination, 24-h ambulatory BP recording, and metabolic (euglycemic hyperinsulinemic glucose clamp and fasting plasma leptin levels) measurements. Left ventricular mass correlated positively only with ambulatory diastolic BP (DBP) values, whereas the indices of myocardial wall growth such as interventricular septum thickness and sum of wall thickness (ie, septal + posterior wall thickness) correlated either with 24 h, daytime, or nighttime DBP, as well as with fasting plasma glucose, fasting plasma leptin, and insulin action after adjustment for age, body mass index (BMI), and waist/hip ratio (WHR). In contrast, plasma leptin concentration did not correlate with clinical and ambulatory BP values. A multiple linear regression analysis allowed to investigate the independent role of main anthropometric and cardiovascular covariates on the sum of wall thickness variability. A model that includes age, BMI, WHR, fasting plasma leptin concentration, plasma Na+ concentration, insulin action, and nighttime DBP explained 68% of the sum of wall thickness variability. In such a model, plasma leptin concentration (P < .001), insulin action (P < .029), and nighttime DBP (P < .002) were significantly and independently associated with myocardial wall thickness. In conclusion, our study demonstrates that in hypertensive men fasting plasma leptin levels are determinant of myocardial wall thickness independently of 24-h BP values.

Elevated plasma fatty acid concentrations prolong cardiac repolarization in healthy subjects

BACKGROUND

High fatty acid concentrations have been shown to stimulate sympathetic nervous system activity, which may modify ventricular repolarization and thus the Q-T interval on electrocardiogram recordings.

OBJECTIVE

The aim of this study was to investigate whether acute elevations of plasma fatty acid concentrations influence the corrected Q-T interval (Q-Tc), Q-Tc dispersion, and sympathetic nervous system activity in healthy nonobese subjects.

DESIGN

Thirty-two healthy subjects (x +/- SD: 48+/-7 y of age) received an infusion of 10% triacylglycerol emulsion plus heparin (a bolus of 200 U followed by 0.2 U min(-1) * kg body wt(-1) for 180 min); on another occasion and in random order, the same subjects received a saline infusion.

RESULTS

Compared with the saline infusion, infusion of 10% triacylglycerol emulsion increased plasma fatty acids (P<0.001) and was associated with an increase in mean blood pressure (P<0.05), heart rate (P<0.05), Q-Tc (P<0.01), Q-Tc dispersion (P<0.01), and plasma epinephrine (P<0.005). Furthermore, individual changes in plasma epinephrine correlated with changes in Q-Tc (r = 0.60, P<0.001) and Q-Tc dispersion (r = 0.53, P< 0.02) even after adjustment for age, sex, and body mass index (P<0.03 for all correlations). Only changes in plasma fatty acids (P = 0.04) and plasma epinephrine (P = 0.006) concentrations were significantly and independently associated with the lengthening of the Q-T interval.

CONCLUSION

Our study showed that elevated plasma fatty acid concentrations might affect cardiac repolarization, at least in part because of an increase in plasma catecholamines.

Blood viscosity and aging

The objective of this study was to evaluate the relationship of whole blood viscosity and its major determinants (plasma fibrinogen level, hematocrit, hemoglobin and blood cell count) to advancing age. A total of 249 subjects (mean age 49.9+/-21.5; range 19-102 years) were included in the study. They were divided into three groups, (A) <30 years of age, n, 58; (B) 30-60 years, n, 107; (C) >60 years, n, 84. Whole blood viscosity at two different rates of shear (450 and 45 s(-1)) was evaluated using a cone-plate digital viscosimeter. The hematological parameters (hematocrit, hemoglobin and blood cell count) were evaluated using an automatic Coulter Counter. Plasma fibrinogen concentration was measured by a clotting method. When both sexes are considered together, whole blood viscosity shows no significant difference among age groups. Plasma fibrinogen concentration significantly increases with age (P<0.001); hemoglobin, red blood cell count and platelet count, on contrary, are significantly lower in aged group. In the male sex, blood viscosity at higher shear rate (450 s(-1)) negatively correlates with advancing age (P<0.005). The age-related decrease of hematocrit value in the male sex accounts for this occurrence.

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.

Hemodynamic effects of acute hyperglycemia in type 2 diabetic patients

OBJECTIVE

The aim of the present study was to evaluate the hemodynamic effects of acute hyperglycemia in type 2 diabetic patients and to see whether these effects are related to changes in nitric oxide (NO) availability.

RESEARCH DESIGN AND METHODS

Twenty newly diagnosed complication-free diet-treated type 2 diabetic patients participated in the study. All patients underwent 3 hyperglycemic glucose clamps in random order: 1) the control study was performed with plasma glucose clamped at 18 mmol/l for 2 h; 2) the octreotide study with plasma insulin blocked at basal levels during the clamp; and 3) the L-arginine study with L-arginine (1 g/min) infused during the last 30 min of the clamp. A group of 8 patients also underwent a glutathione infusion (600 mg as an intravenous bolus followed by 5 mg/min infusion) during the clamp.

RESULTS

During hyperglycemia, there were significant increments of systolic (sBP) (from 115.5 +/- 9.1 to 120.3 +/- 8.2 mmHg, P < 0.01) and diastolic (dBP) (from 70.3 +/- 7.8 to 79.7 +/- 5.3 mmHg, P < 0.01) blood pressure, as well as heart rate (from 75.2 +/- 7.8 to 80.8 +/- 5.4 beats/min, P < 0.01) and plasma catecholamines (P < 0.05). Squatting ratios, a measure of the baroreflex activity, significantly deteriorated after hyperglycemia (P < 0.01). The infusion of octreotide, used to avoid the possible confounding influence of insulin, did not change the hemodynamic effects of hyperglycemia. Glutathione, a free radical scavenger, completely prevented the vascular effects of hyperglycemia. L-Arginine produced a fall in sBP and dBP to baseline values and normalized squatting ratios.

CONCLUSIONS

Acute hyperglycemia in newly diagnosed type 2 diabetic patients causes significant hemodynamic changes that are independent of endogenous insulin and are prevented by glutatione and reversed by L-arginine, suggesting an interference with endogenous NO availability. These observations could help explain the adverse cardiovascular effects of hyperglycemic spikes.

The effect of acute hyperglycaemia on QTc duration in healthy man

AIMS/HYPOTHESIS

Prolongation of heart rate-adjusted QT (QTc) is associated with an increased risk of coronary heart disease and sudden death. The objective of this study was to investigate whether acute increases of plasma glucose concentrations in healthy subjects could influence QTc and QTc dispersion.

METHODS

Plasma glucose concentrations were quickly raised to 15 mmol/l in 20 healthy subjects (10 men/10 women) and maintained for 2 h. On another occasion, and in random order, all subjects underwent the same hyperglycaemic clamp as above and an infusion of the somatostatin analogue octreotide (25 microg as iv bolus followed by a 0.5 g/min infusion) to block the release of endogenous insulin.

RESULTS

Systolic and diastolic blood pressures, heart rate and plasma catecholamine concentrations showed significant increases (p < 0.05) starting after 60 min of hyperglycaemia. QTc, QTc dispersion and PR interval also showed significant increments at 120 min of the hyperglycaemic clamp. The infusion of octreotide did not influence QTc duration, QTc dispersion, PR interval and the haemodynamic effects of acute hyperglycaemia.

CONCLUSION/INTERPRETATION

The results show that acute hyperglycaemia produces significant increments of QTc and QTc dispersion in normal subjects. In this context, endogenously released insulin during acute hyperglycaemia seems to play a minor part.

Impairment of endothelial functions by acute hyperhomocysteinemia and reversal by antioxidant vitamins

CONTEXT

Increased levels of homocysteine are associated with risk of cardiovascular disease. Homocysteine may cause this risk by impairing endothelial cell function.

OBJECTIVE

To evaluate the effect of acute hyperhomocysteinemia with and without antioxidant vitamin pretreatment on cardiovascular risk factors and endothelial functions.

DESIGN AND SETTING

Observer-blinded, randomized crossover study conducted at a university hospital in Italy.

SUBJECTS

Twenty healthy hospital staff volunteers (10 men, 10 women) aged 25 to 45 years.

INTERVENTIONS

Subjects were given each of 3 loads in random order at 1-week intervals: oral methionine, 100 mg/kg in fruit juice; the same methionine load immediately following ingestion of antioxidant vitamin E, 800 IU, and ascorbic acid, 1000 mg; and methionine-free fruit juice (placebo). Ten of the 20 subjects also ingested a placebo load with vitamins.

MAIN OUTCOME MEASURES

Lipid, coagulation, glucose, and circulating adhesion molecule parameters, blood pressure, and endothelial functions as assessed by hemodynamic and rheologic responses to L-arginine, evaluated at baseline and 4 hours following ingestion of the loads.

RESULTS

The oral methionine load increased mean (SD) plasma homocysteine level from 10.5 (3.8) micromol/L at baseline to 27.1 (6.7) micromol/L at 4 hours (P<.001). A similar increase was observed with the same load plus vitamins (10.0 [4.0] to 22.7 [7.8] micromol/L; P<.001) but no significant increase was observed with placebo (10.1 [3.7] to 10.4 [3.2] micromol/L; P=.75). Coagulation and circulating adhesion molecule levels significantly increased after methionine ingestion alone (P<.05) but not after placebo or methionine ingestion with vitamins. While the mean (SD) blood pressure (-7.0% [2.7%]; P<.001), platelet aggregation response to adenosine diphosphate (-11.4% [4.5%]; P=.009) and blood viscosity (-3.0% [1.2%]; P=.04) declined in these parameters 10 minutes after an L-arginine load (3 g) following placebo, the increase after methionine alone (-2.3% [1.5%], 4.0% [3.0%], and 1.5% [1.0%], respectively; P<.05), did not occur following methionine load with vitamin pretreatment (-6.3% [2.5%], -7.9% [3.5%], and -1.5% [1.0%], respectively; P=.24).

CONCLUSION

Our data suggest that mild to moderate elevations of plasma homocysteine levels in healthy subjects activate coagulation, modify the adhesive properties of endothelium, and impair the vascular responses to L-arginine. Pretreatment with antioxidant vitamin E and ascorbic acid blocks the effects of hyperhomocysteinemia, suggesting an oxidative mechanism.

Effects of perindopril and carvedilol on endothelium-dependent vascular functions in patients with diabetes and hypertension

OBJECTIVE

To compare the effects of the ACE inhibitor perindopril and the beta-blocker carvedilol on blood pressure and endothelial functions in NIDDM patients with hypertension.

RESEARCH DESIGN AND METHODS

We conducted a double-blind randomized trial in 26 patients with NIDDM and mild hypertension. A 4-week run-in placebo period preceded the active 12-week treatment with perindopril (4-8 mg daily) or carvedilol (25-50 mg daily). Endothelial functions were assessed by evaluating the hemodynamic (mean blood pressure, leg blood flow) and rheological (platelet aggregation, blood viscosity, and blood filterability) responses to an intravenous bolus of 3 g L-arginine, the natural precursor of nitric oxide.

RESULTS

Both perindopril and carvedilol significantly reduced mean blood pressure (P < 0.001) and increased leg blood flow (P < 0.05) to the same extent; blood filterability remained unchanged in both perindopril- and carvedilol-treated groups. Carvedilol reduced platelet aggregation and blood viscosity significantly (P < 0.05) but perindopril did not. Before treatment, the hemodynamic and rheologic responses to L-arginine were significantly lower in patients (P < 0.05-0.01) than in 20 nondiabetic nonhypertensive control subjects. After 12 weeks of treatment, both drugs normalized the hemodynamic responses to L-arginine. Platelet aggregation response to L-arginine was ameliorated by carvedilol and remained unchanged in the perindopril group.

CONCLUSIONS

At the doses used, both drugs effectively reduce blood pressure and normalize the hemodynamic responses to L-arginine. The implications of the ameliorated endothelial function for the poor cardiovascular outlook of the NIDDM hypertensive patient need further assessment.

Hemodynamic and metabolic effects of transdermal clonidine in patients with hypertension and non-insulin-dependent diabetes mellitus

The aim of this study was to evaluate the effect of transdermal clonidine on hemodynamic and metabolic parameters in patients who have elevated blood pressure and non-insulin-dependent diabetes mellitus (NIDDM). After a 2-week run in placebo period, 20 NIDDM patients who had diastolic blood pressure in the range of 90 to 105 mm Hg underwent a randomized, single blind, placebo controlled, cross-over study of 4 week treatment with clonidine (transdermal patch 2.5 mg/week) or placebo (inactive patch). Compared with placebo, clonidine significantly reduced systolic (153 +/- 6 v 163 +/- 8) and diastolic (88 +/- 2 v 98 +/- 3.5 mm Hg, P = .001) blood pressure, left ventricular mass (94 +/- 11 v 99 +/- 12 g/m2, P < .01) and fasting glucose levels. Total glucose disposal (glucose clamp) was 6.5 +/- 1.5 with placebo and 7.1 +/- 1.6 mg/kg/min with clonidine (P < .01). Oxidative glucose disposal (indirect calorimetry) was also greater after clonidine. Plasma glucose, insulin, and C-peptide responses following oral glucose (75 g) were significantly lower after clonidine, as well as urinary albumin excretion. Transdermal clonidine is effective in reducing blood pressure in hypertensive NIDDM patients and is well tolerated. It may be useful to reduce the cardiovascular impact of hypertension in diabetes mellitus.

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.

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.

Metabolic and cardiovascular effects of carvedilol and atenolol in non-insulin-dependent diabetes mellitus and hypertension. A randomized, controlled trial

BACKGROUND

Diabetic patients are considered less suitable than nondiabetic patients for beta-blocker therapy because of the risk for worsened glucose and lipid metabolism and more severe hypoglycemic attacks.

OBJECTIVE

To compare the metabolic and cardiovascular effects of carvedilol with those of atenolol in diabetic patients with hypertension.

DESIGN

Randomized, double-blind, 24-week trial.

SETTING

University hospital clinic.

PATIENTS

45 patients with non-insulin-dependent diabetes mellitus and hypertension.

INTERVENTION

After a 4- to 6-week run-in period during which placebo was given in a single-blind manner, patients were randomly assigned to carvedilol or atenolol.

MEASUREMENTS

An oral glucose tolerance test; assessment of insulin sensitivity and hormonal responses to insulin hypoglycemia; and assessment of lipid levels, blood pressure, left ventricular mass, and lipid peroxidation.

RESULTS

Changes in systolic and diastolic blood pressure and left ventricular mass index were similar with carvedilol and atenolol (P > 0.2). Fasting plasma glucose and insulin levels decreased with carvedilol and increased with atenolol. Responses to carvedilol were greater than those to atenolol, as follows: increase in total glucose disposal, 9.54 mumol/kg of body weight per minute (95% CI, 7 to 11.9 mumol/kg per minute); decrease in plasma glucose response to oral glucose, 61 mmol/L x 180 minutes (CI, -101 to -21 mmol/L x 180 minutes); decrease in insulin response to oral glucose, 6.2 nmol/L x 180 minutes (CI, -9.8 to -2.6 nmol/L x 180 minutes); decrease in triglyceride level, 0.56 mmol/L (CI, -0.75 to -0.37 mmol/L; P < 0.001); increase in high-density lipoprotein cholesterol level, 0.13 mmol/L (CI, 0.09 to 0.17 mmol/L; P < 0.001); and decrease in lipid peroxidation, 0.25 mumol/L (CI, -0.34 to -0.16 mumol/L).

CONCLUSIONS

By improving glucose and lipid metabolism and reducing lipid peroxidation, carvedilol may offer advantages in patients with diabetes and hypertension.

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.

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.