Effects of L-arginine on lower limb vasodilator reserve and exercise capacity in patients with chronic heart failure

Effect of l-arginine on cardiac reverse remodeling and quality of life in patients with heart failure

BACKGROUND & AIMS

Heart failure (HF), as a major cardiac disease, is associated with considerable mortality, morbidities and poor quality of life. The aim of this study was to investigate the effect of l-arginine supplementation on cardiac outcomes and quality of life in patients with ischemic HF.

METHODS

This double-blind randomized controlled clinical trial was conducted in 50 patients with ischemic HF. Patients were randomly assigned to receive either 3 gr/d l-arginine or placebo, for 10 weeks. Cardiac function (based on echocardiography and six-minute walk test), blood pressure, and quality of life (based on the Minnesota living with heart failure questionnaire) were assessed.

RESULTS

The results showed significant improvements in ejection fraction (-6.5 ± 8.7 vs. -0.7 ± 7.8%, P = 0.037), left ventricular function (P = 0.043), diastolic dysfunction (P = 0.01) and marginally improvement in changes of left ventricular dimension during diastole (LVDd) (4 ± 6 vs. 0.3 ± 6.9 mm, P = 0.065) in the l-arginine compared to the placebo group. At the end of the study, physical aspect (5.7 ± 3.3 vs. 1.2 ± 6.1, P = 0.002) and total score (10 ± 6.7 vs. 4.1 ± 9.4, P = 0.011) of quality of life improved significantly in the l-arginine compared with the placebo group. Additionally, pre-to post-values of diastolic blood pressure, mean arterial pressure, LVDd, LV ejection fraction, left ventricular function, diastolic dysfunction as well as physical and total scores of quality of life improved significantly within the intervention, but not the placebo, group (all P < 0.05).

CONCLUSION

This study showed that 3 gr/d l-arginine supplementation for 10 weeks could improve cardiac recovery and function, and quality of life in patients with HF. This study was registered at the Iranian Clinical Trial Registration Center (www.irct.ir) with IRCT20170202032367N4 code.

No effect of short-term arginine supplementation on nitric oxide production, metabolism and performance in intermittent exercise in athletes

Arginine supplementation has been shown to alleviate endothelial dysfunction and improve exercise performance through increasing nitric oxide production in patients with cardiopulmonary diseases. In addition, arginine supplementation could decrease accumulations of lactate and ammonia, metabolites involved in development of muscular fatigue. The aim of this study was to investigate the effect of short-term arginine supplementation on performance in intermittent anaerobic exercise and the underlying mechanism in well-trained male athletes. Ten elite male college judo athletes participated with a randomized crossover, placebo-controlled design. The subjects consumed 6 g/day arginine (ARG trial) or placebo (CON trial) for 3 days then performed an intermittent anaerobic exercise test on a cycle ergometer. Blood samples were collected before supplementation, before and during exercise and 0, 3, 6, 10, 30 and 60 min after exercise. ARG trial had significantly higher arginine concentrations than CON trial at the same time point before, during and after exercise. In both trials, nitrate and nitrite concentration was significantly higher during and 6 min after exercise comparing to the basal concentration. The increase in nitrate and nitrite concentration during exercise in both trials was parallel to the increase in plasma citrulline concentrations. There was no significant difference between the 2 trials in plasma nitrate and nitrite, lactate and ammonia concentrations and peak and average power in the exercise. The results of this study suggested that short-term arginine supplementation had no effect on nitric oxide production, lactate and ammonia metabolism and performance in intermittent anaerobic exercise in well-trained male athletes.

Low-dose L-arginine administration increases microperfusion of hindlimb muscle without affecting blood pressure in rats

The objective of this work was to evaluate the influence of exogenous L-arginine on the capillary blood flow of peripheral tissues of normotensive subjects. Rats were anesthetized with sodium pentobarbital, and the blood flow of femoral, dorsal, and ventral skin and gastrocnemius and soleus muscle was measured by laser Doppler flow and microsphere methods to compare the blood flow before and after the L-arginine infusion. L-arginine lowered the mean blood pressure in a dose-dependent manner, but a statistically significant reduction in mean blood pressure was detected only at a high dose of 500 mg/kg of body weight. The significant blood flow increment was detected after the L-arginine infusion at doses of 50 and 150 mg/kg without causing hypotension. Nicardipine, a calcium channel blocker, also increased the skin blood flow, but the blood flow increment and blood pressure fall were comparable. A significant increment in microperfusion was detected in gastrocnemius, soleus muscle, and ventral skin compared with control group by the microsphere method. No adverse effects were observed during L-arginine and microsphere infusion. The present work indicates that l-arginine infusion increases muscle capillary blood flow in rats that are not performing exercise. Supplementation with l-arginine might provide additional blood flow at rest and during exercise and result in the improvement of muscle performance and exercise capacity.

Effects of L-arginine supplementation on exercise metabolism

PURPOSE OF REVIEW

To describe the influence of acute and chronic administration of L-arginine on metabolism at rest and during exercise.

RECENT FINDINGS

There has been substantial examination of the effect of infusion and ingestion of L-arginine at rest. It has been clearly demonstrated that L-arginine administration improves endothelial function in various disease states. In addition, L-arginine infusion at rest increases plasma insulin, growth hormone, glucagon, catecholamines and prolactin. Such hormonal changes affect metabolism. There has, however, been very little examination of the effect of increases in L-arginine availability during exercise. This is important to study as there is preliminary evidence that L-arginine infusion, probably via increases in nitric oxide (NO), alters skeletal-muscle metabolism during exercise. There is a need for further research, especially to understand the mechanisms of how L-arginine affects exercise metabolism and also to determine whether the hormonal responses that occur in response to L-arginine at rest are also present to some extent during exercise.

SUMMARY

This line of research may have important therapeutic implications as there are indications that L-arginine augments the effects of exercise training on insulin sensitivity and capillary growth in muscles.

L-Arginine infusion increases glucose clearance during prolonged exercise in humans

Nitric oxide synthase (NOS) inhibition has been shown in humans to attenuate exercise-induced increases in muscle glucose uptake. We examined the effect of infusing the NO precursor L-arginine (L-Arg) on glucose kinetics during exercise in humans. Nine endurance-trained males cycled for 120 min at 72+/-1% Vo(2 peak) followed immediately by a 15-min "all-out" cycling performance bout. A [6,6-(2)H]glucose tracer was infused throughout exercise, and either saline alone (Control, CON) or saline containing L-Arg HCL (L-Arg, 30 g at 0.5 g/min) was confused in a double-blind, randomized order during the last 60 min of exercise. L-Arg augmented the increases in glucose rate of appearance, glucose rate of disappearance, and glucose clearance rate (L-Arg: 16.1+/-1.8 ml.min(-1).kg(-1); CON: 11.9+/- 0.7 ml.min(-1).kg(-1) at 120 min, P<0.05) during exercise, with a net effect of reducing plasma glucose concentration during exercise. L-Arg infusion had no significant effect on plasma insulin concentration but attenuated the increase in nonesterified fatty acid and glycerol concentrations during exercise. L-Arg infusion had no effect on cycling exercise performance. In conclusion, L-Arg infusion during exercise significantly increases skeletal muscle glucose clearance in humans. Because plasma insulin concentration was unaffected by L-Arg infusion, greater NO production may have been responsible for this effect.

Muscle metaboreflex is blunted with reduced vascular resistance response of nonexercised limb in patients with chronic heart failure

BACKGROUND

Exercise-mediated muscle metaboreflex (MMR) activates the sympathetic nervous system afferently and may play an important role in the reduction in blood flow in nonexercised limb, thus enhancing exercised skeletal muscle blood flow (ie, normal regional blood flow redistribution during exercise). However, few data are available to describe the relationship between MMR and peripheral vascular control during exercise in congestive heart failure (CHF). The aim of this study was to determine whether MMR is impaired in CHF, and, if so, whether MMR is related to clinical severity of CHF and to changes in nonexercised limb vascular resistance in CHF.

METHODS AND RESULTS

Eleven CHF patients and 9 healthy age- and gender-matched controls were examined. All subjects performed a rhythmic handgrip exercise test at 50% of maximal voluntary contraction for 3 minutes on 2 occasions with and without postexercise upper arm regional circulatory occlusion (RCO/non-RCO). Changes in systolic blood pressure were measured and plotted against protocol time for both RCO and non-RCO. The area under each curve was estimated, and the calculating difference in the area between RCO and non-RCO was regarded as MMR. In addition, changes in calf vascular resistance were measured continuously by plethysmography after the handgrip test and the area differences between the RCO and non-RCO data was taken to represent MMR-provoked resistance changes in the nonexercised limb. During the handgrip exercise, systolic blood pressure increased similarly on the 2 occasions for both groups. MMR was significantly lower in CHF patients than in controls (68.2 +/- 23.1 versus 160.4 +/- 29.6 arbitrary units; P < .05). Decrease in MMR activity was related to clinical severity of CHF (controls, 160.4 +/- 29.6; New York Heart Association class II, 87.6 +/- 29.8; New York Heart Association class III, 34.3 +/- 34.8 arbitrary units; P < .05). The increase in calf vascular resistance between RCO and non-RCO protocols in the control group was significant (+146.5 +/- 38.0 arbitrary units; P < .05), whereas the difference in the CHF group was not significant (-72.9 +/- 126.9 arbitrary units; not significant).

CONCLUSIONS

Exercise-induced MMR control in mild to moderate CHF is impaired in association with a blunted increase in nonexercised limb vascular resistance. This suggests that blunted MMR activity impairs regional blood flow redistribution and may contribute in part to exercise intolerance in this disorder.

An age-related decline in endothelial function is not associated with alterations in L-arginine transport in humans

OBJECTIVES

Endothelial dysfunction is established in aged individuals; however, the mechanism(s) are not fully elucidated. We have previously identified l-arginine transport as a potential rate-limiting factor in nitric oxide (NO) production in heart-failure patients, characterized with endothelial dysfunction. We therefore aimed to investigate whether the age-related decline in endothelial function is due to reduced transport of the NO precursor, L-arginine.

METHODS

Thirty-seven healthy males aged between 19 and 69 were recruited. Throughout 40 min of intra-arterial (i.a.) infusion of [3H]L-arginine (100 nCi/min), venous blood samples were withdrawn for the determination of L-arginine clearance. Venous occlusion plethysmography was then used to record the forearm blood flow responses to i.a. infusions of acetylcholine (ACh; 9.25 and 37 microg/min) and sodium nitroprusside (SNP; 2 and 8 microg/min).

RESULTS

While ACh-induced vasodilation decreased with age (37 microg/min; young 15.87 +/- 1.30, middle-aged 9.59 +/- 1.33, older 10.42 +/- 1.12 ml/min per 100 ml tissue; P = 0.001), there was no change in forearm [3H]L-arginine clearance (young 126.08 +/- 19.05, middle-aged 122.47 +/- 20.96, older 126.56 +/- 19.56 ml/min; NS). Further [3H]L-arginine uptake studies in isolated peripheral blood mononuclear cells supported our in vivo findings, demonstrating no difference in [3H]L-arginine transport across the age spectrum.

CONCLUSIONS

The present study excludes the hypothesis of impaired L-arginine transport as a potential mechanism for the age-related decline in endothelial function.

Local vascular responses affecting blood flow in postural tachycardia syndrome

Postural tachycardia syndrome (POTS) is defined by orthostatic intolerance associated with abnormal upright tachycardia. Some patients have defective peripheral vasoconstriction and increased calf blood flow. Others have increased peripheral arterial resistance and decreased blood flow. In 14 POTS patients (13-19 yr) evenly subdivided among low-flow POTS (LFP) and high-flow POTS (HFP) we tested the hypothesis that myogenic, venoarteriolar, and reactive hyperemic responses are abnormal. We used venous occlusion plethysmography to measure calf venous pressure and blood flow in the supine position and when the calf was lowered by 40 cm to evoke myogenic and venoarteriolar responses and during venous hypertension by 40-mmHg occlusion to evoke the venoarteriolar response. We measured calf reactive hyperemia with plethysmography and cutaneous laser-Doppler flowmetry. Baseline blood flow in LFP was reduced compared with HFP and control subjects (0.8 +/- 0.2 vs. 4.4 +/- 0.5 and 2.7 +/- 0.4 ml.min-1.100 ml-1) but increased during leg lowering (1.2 +/- 0.5 ml.min-1. 100 ml-1) while decreasing in the others. Baseline peripheral arterial resistance was increased in LFP and decreased in HFP compared with control subjects (39 +/- 13 vs. 15 +/- 3 and 22 +/- 5 mmHg.ml-1. 100 ml. min) but decreased to 29 +/- 13 mmHg.ml-1.100 ml. min in LFP during venous hypertension. Resistance increased in the other groups. Maximum calf hyperemic flow and cutaneous flow were similar in all subjects. The duration of hyperemic blood flow was curtailed in LFP compared with either control or HFP subjects (plethysmographic time constant = 20 +/- 2 vs. 29 +/- 4 and 28 +/- 4 s; cutaneous time constant = 60 +/- 25 vs. 149 +/- 53 s in controls). Local blood flow regulation in low-flow POTS is impaired.

Acute and chronic endothelial dysfunction: implications for the development of heart failure

Heart failure has been characterized by a reduction in cardiac contractile function resulting in reduced cardiac output. The clinical symptoms including mild tachycardia, reduced arterial pressure, increased venous or filling pressure and exercise intolerance have conceptually, to a large degree, been attributed to cardiac myocyte dysfunction. More recently, a vascular component has been recognized to contribute to heart failure. Among the most studied vascular mechanisms that might contribute to the development of heart failure has been the reduced production of nitric oxide or the reduced bioactivity of NO associated with both basic models of heart failure and disease in patients. The still evolving concept that heart failure is a cytokine activated state has, in addition, focused attention on the possibility that the cytokine driven isoform of NO synthase (NOS), iNOS, may produce sufficient quantities of NO to actually suppress cardiac myocyte function contributing to the reduced inotropic state in the failing heart. Thus, our view of the role of NO in the development of heart failure has evolved from simply a reduction in production of NO in blood vessels, to altered substrate availability (i.e. L-arginine), to increased scavenging of NO by superoxide anion, to increased production of NO from iNOS. As these concepts develop, our approach to the therapeutics of heart failure has also progressed with the recognition of the need to develop treatments directed towards addressing one or more of these etiologies. This review will focus on these aspects of the involvement of NO in the development of heart failure and some of the treatments that have developed from our understanding of the basic biology of NO to address these pathohysiologic states.

L-arginine in cardiovascular disease: dream or reality?

L-arginine is the substrate for endothelial nitric oxide synthase (eNOS), and the precursor for the synthesis of nitric oxide (NO). This amino acid exerts a number of actions in the cardiovascular system, mainly through the production of NO. However, it also has a number of NO-independent properties, such as the ability to regulate blood and intracellular pH and the effect on the depolarization of endothelial cell membranes. It also has antihypertensive and antioxidant properties, it influences blood viscosity and the coagulation/fibrinolysis system, and it affects the metabolism of glucose, lipids and proteins. L-arginine influences a number of atherosclerosis risk factors such as hypercholesterolemia, hypertension and smoking, improving endothelial function in these patients. However, it does not affect endothelial function in patients with diabetes mellitus. The role of L-arginine in coronary artery disease is still controversial, but it seems that oral or parenteral administration of this amino acid restores endothelial function in the brachial artery and improves coronary microcirculation. The role of L-arginine in heart failure is currently under investigation, and the first results are rather hopeful. In conclusion, L-arginine seems to provide a hopeful prospect for the treatment of cardiovascular diseases. However, more data derived from large-scale prospective studies evaluating the effects of long-term treatment with L-arginine are needed.

Therapeutic modification of the L-arginine-eNOS pathway in cardiovascular diseases

L-Arginine is the substrate for nitric oxide production. Endothelium dysfunction could be attributed to L-arginine deficiency or the presence of L-arginine endogenous inhibitors. This hypothesis leads to the assumption that provision of L-arginine could be the key for endothelial function improvement. Many studies have proven that L-arginine has a beneficial effect on endothelium dependent vasoreactivity, as well as on the interaction between vascular wall, platelets and leucocytes. Therefore, individuals with risk factors for atherosclerosis and patients with coronary artery disease or heart failure, could benefit from therapy with L-arginine.

Peripheral vascular remodeling in chronic heart failure: clinical relevance and new conceptualization of its mechanisms

Increased peripheral vascular tone is a critical factor in the deterioration of clinical stage and symptoms in chronic congestive heart failure (CHF) because of increased cardiac afterload and decreased nutritive skeletal muscle blood flow. Endothelial function as represented by nitric oxide (NO) production shows significant attenuation with the progression of clinical severity of CHF as determined by New York Heart Association class and exercise capacity parameters. This endothelial dysfunction emerges in the early stages of CHF. In the advanced stage of the condition, both endothelium-dependent and endothelium-independent dilator mechanisms are impaired in limb resistance vessels. This occurs because vascular endothelial function, especially NO production, is an important factor in the regulation of vasodilatory function, as well as making an important contribution to vascular structure. Furthermore, although such vasodilatory circulating factors as natriuretic polypeptides and newly discovered adrenomedullin are increased in heart failure, the vasodilatory potency of these polypeptide hormones in the limb vascular bed is significantly blunted. These observations suggest that peripheral circulatory failure in CHF is caused not only by simple arterial muscle constriction, but also by structural and functional changes, including receptor and postreceptor levels in the vasculature. This vascular remodeling may be an important mechanism underlying vasodilatory failure in both limb conduit and intraskeletal muscle vessels and may contribute significantly to left ventricular dysfunction and exercise intolerance in patients with heart failure.