Research

L-arginine-induced vasodilation in healthy humans: pharmacokinetic-pharmacodynamic relationship.

AIMS:

Administration of L-arginine by intravenous infusion or via oral absorption has been shown to induce peripheral vasodilation in humans, and to improve endothelium-dependent vasodilation. This Clinical Trial investigated the pharmacokinetics and pharmacokinetic-pharmacodynamic relationship of L-arginine after a single intravenous infusion of 30 g or 5 g, or after a single oral application of 5 g, as compared with the respective placebo, in eight healthy male human subjects.

METHODS:

The vasodilator effects of L-arginine were assessed non-invasively by blood pressure monitoring and impedance cardiograph. Urinary nitrate and cyclic GMP excretion rates were measured as non-invasive indicators of endogenous Nitric Oxide production.

RESULTS:

Plasma L-arginine levels increased to (mean +/- s.e.mean) 6223+/-407 (range, 5100-7680) and 822+/-59 (527-955) micromol l(-1) after intravenous infusion of 30 g and 5 g L-arginine, respectively, and to 310+/-152 (118-1219) micromol l(-1) after oral ingestion of 5 g L-arginine. Oral bioavailability of L-arginine was 68+/-9 (51-87)%. Clearance was 544+/-24 (440-620), 894+/-164 (470-1190), and 1018+/-230 (710-2130) ml min(-1), and elimination half-life was calculated as 41.6+/-2.3 (34-55), 59.6+/-9.1 (24-98), and 79.5+/-9.3 (50-121) min, respectively, for 30 g i.v., 6 g i.v., and 6 g p.o. of L-arginine.

Blood pressure and total peripheral resistance were significantly decreased after intravenous infusion of L-arginine. After infusion of 5 g L-arginine, urinary nitrate excretion also significantly increased, (nitrate by 47+/-12% [P<0.05], cyclic GMP by 67+/-47% [P= ns]), although to a lesser and more variable extent than after 30 g of L-arginine.

The onset and the duration of the vasodilator effect of L-arginine and its effects on endogenous Nitric Oxide production closely corresponded to the plasma concentration half-life of L-arginine, as indicated by an equilibration half-life of 6+/-2 (3.7-8.4) min between plasma concentration and effect in pharmacokinetic-pharmacodynamic analysis, and the lack of hysteresis in the plasma concentration-versus-effect plot.

CONCLUSIONS:

The vascular effects of L-arginine are closely correlated with its plasma concentrations. This data may provide a basis for the utilization of L-arginine in cardiovascular diseases.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1873701/

Short-term effects of L-citrulline supplementation on arterial stiffness in middle-aged men.

BACKGROUND:

Nitric oxide plays a key role in the maintenance of vascular tone, contributing to the functional regulation of arterial stiffness.

OBJECTIVE:

This Clinical Trial examined the short-term effects of L-citrulline supplementation on arterial stiffness in humans.

METHODS:

In a double-blind, randomized, placebo-controlled parallel-group trial, 15 healthy male subjects (age: 58.3 ± 4.4 years) with brachial-ankle pulse wave velocity (baPWV; index of arterial stiffness >1400 cm/sec) were given 5.6g/day of L-citrulline or placebo for 7 days. baPWV and various clinical parameters were measured before (baseline) and after oral supplementation of L-citrulline or placebo.

RESULTS:

Compared with the placebo group, baPWV was significantly reduced in the L-citrulline group (p<0.01). The serum nitrogen oxide (NOx, the sum of nitrite plus nitrate) and Nitric Oxide metabolic products were significantly increased only in the L-citrulline group (p<0.05). Plasma citrulline, arginine and the ratio of arginine/asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase (arginine/ADMA ratio) were significantly increased in the L-citrulline group compared with the placebo group (p<0.05, p<0.01, p<0.05, respectively). Moreover, there was a correlation between the increase of plasma arginine and the reduction of baPWV (r=-0.553, p<0.05).

CONCLUSION:

These findings suggest that L-citrulline supplementation may functionally improve arterial stiffness, independent of blood pressure, in humans.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pubmed/21067832

Diabetes is becoming a pandemic and numbers are expected to rise to 366 million (4.4 % of the global population) by 2030. In diabetic patients, long-term damage, dysfunction, and failure of different organs, especially the eyes (diabetic retinopathy), kidneys (diabetic nephropathy), nerves (diabetic neuropathy), heart (myocardial infarction), and blood vessels (atherosclerosis) are related to uncontrolled hyperglycaemia. Hyperglycaemia induces oxidative stress primarily by ROS. (Reactive Oxygen Species).

There is convincing experimental and clinical evidence that the generation of ROS increases in both types of diabetes and that the onset of diabetes is closely associated with oxidative stress. Vitamin C has been associated with decreased risk of developing diabetes mellitus (DM).

In Norfolk Prospective Study the association between fruit and vegetable intake and plasma levels of vitamin C and risk of type 2 DM was established. During 12-years of follow-up, 735 incident cases of diabetes were identified among nearly 21,000 participants. A significant inverse association was found between plasma levels of vitamin C and risk of diabetes (odds ratio = 0.38, 95 % confidence interval: 0.28–0.52). This is further supported by a study with longer follow up of 23 years which reported that antioxidants induced risk reduction of type 2 diabetes and vitamin C level was found to be significantly lower in both insulin dependent and non-dependent diabetes. Vitamin C reduces fasting and postprandial oxidative stress. Sharma et al. have observed reduced vitamin C levels in diabetic subjects. They further reported that vitamin C level is also associated with various components of metabolic syndrome and with the increment in component there is a sharp reduction in vitamin C level. In recent experimental studies it has been found that Vitamin C supplementation relieves oxidative stress in the blood and tissues of diabetic aged rats by modulating the antioxidant system and lipid profile.

Diabetes is associated with various micro vascular and macro vascular complications. Hyperglycaemia in diabetes is responsible for micro vascular ROS generation which causes endothelial dysfunction and vitamin C blocks acute hyperglycaemic impairment of endothelial function in diabetic subjects. The role of vitamin C in diabetic retinopathy has also been reported in various studies. Vitamin C supplementation reduces neovascularization, prevent the inhibition of retinal glutathione reductase, glutathione peroxidase and superoxide dismutase activities; hence vitamin C prevents oxidative stress induced retinopathy.

Conclusion:

Vitamin C has a diverse role as an antioxidant protecting the immune cells against intracellular ROS production during inflammatory response, acting as an enzymatic cofactor and maintaining tissue integrity and plays a crucial role in formation of skin, epithelial and endothelial barriers. Vitamin C supplementation has been found to be beneficial in various inflammatory conditions and in improving, supporting and maintaining the health of the cardiovascular system.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4911847/

The Potential Benefits Beetroot Extract Supplementation in Health and Disease

The recent interest in beetroot extract has been primarily driven by the discovery that sources of dietary nitrate may have important implications for managing cardiovascular health.

Recent studies have provided compelling evidence that beetroot extract ingestion offers beneficial physiological effects that may translate to improved clinical outcomes for several pathologies, such as; hypertension, atherosclerosis, type 2 diabetes and dementia. Hypertension in particular has been the target of many therapeutic interventions and there are numerous studies that show beetroot, delivered acutely as a juice extract supplement significantly reduce systolic and diastolic blood pressure.

Beetroot’s effect on the vasculature is largely attributed to its high inorganic nitrate content. Nitrate itself is not considered to mediate any specific physiological function; rather, nitrates beneficial effects are attributed to its in vivo reduction to nitric oxide (NO), a multifarious messenger molecule with important vascular and metabolic functions.

Nitrate delivered via a beetroot extract source is metabolised to nitrite, which can be further reduced to produce NO. The conversion of nitrite to NO can be catalysed by many molecules with reductase potential (i.e., electron donors), and to date, several proteins (i.e., deoxymyoglobin, xanthine oxidoreductase) and antioxidants (i.e., vitamin C) have been reported to facilitate this reduction. One of the most important functions of endogenous NO is to maintain endothelial function. The endothelium plays a critical role in the regulation of vascular homeostasis by maintaining thrombotic activity, platelet function, vascular tone and the delicate balance between the release of vasodilating (i.e., NO, prostacyclin) and vasoconstricting agents (i.e., endothelin-1, thromboxane). Because NO mediates many of the endothelium’s functions, a depletion in NO availability, as seen with aging, has been singled out as the principal cause of endothelial dysfunction. Endothelial dysfunction is proposed as a primary risk factor for several cardiovascular disorders and has been implicated in the pathogenesis of hypertension and atherosclerosis. Therefore, beetroot extract, as a natural NO donor, has been explored as a nutritional approach to preserve or restore endothelial function.

Webb et al.  were the first to investigate the effects of a beetroot extract supplement on endothelial function in healthy participants. They measured brachial artery (BA) endothelial function using the flow mediated dilation technique (FMD), which involved calculating BA dilation before and after a 20-min ischemic insult. The ischemic procedure (BA occlusion) was effective at inducing endothelial dysfunction, as evidenced by the 60% decrease from pre-to post BAFMD response. However, when participants were pre-treated 2 h prior with a single serving of beetroot juice (500 mL; 23 mmol of nitrate) the BAFMD response was maintained at pre-ischemic levels, suggesting that beetroot juice acted to preserve endothelial function.

Hobbs et al. extended these findings, examining the acute intake of a novel beetroot enriched bread (100 g beetroot, nitrate; 1.1 mmol) on micro vascular function and peripheral arterial stiffness in young healthy males. Although arterial stiffness, assessed by pulse wave velocity and augmentation index, was unaffected by the intervention, the beetroot bread increased micro vascular vasodilation, as measured by changes in cutaneous perfusion using laser doppler imaging (LDI). Endothelium-independent vasodilation (perfusion units) was ~343% greater in the 6 h after ingesting the beetroot enriched bread compared to the control bread. Importantly, this study provided evidence that even a small nitrate load (1.1 mmol) can augment marked improvements in intravascular function. Similar vascular effects were also reported in a study with older populations. Using apparently healthy but slightly obese, older participants (~61 years), Joris and Mensink, investigated whether beetroot juice supplementation would prevent postprandial impairments in BAFMD. In a randomized crossover design, BAFMD response fell by ~1.6% in the control condition, whereas after beetroot juice (140 mL, nitrate; 500 mg) the impairment was only ~0.4%, indicative of a beetroot-mediated protective effect on postprandial endothelial function.

However, nitrate is not the only constituent of beetroot extract proposed to have beneficial effects in health and disease. Beetroot is a rich source of phytochemical compounds that includes ascorbic acid, carotenoids, phenolic acids and flavonoids.

Studies report that beetroot, in the form of an extract supplement, protects against oxidative damage to DNA, lipid and protein structures in vitro. A study by Wootton-Beard and Colleagues suggests that a key mechanism by which beetroot extract exerts its antioxidant effects is by scavenging radical species.

Beetroot extract has emerged as a potent anti-inflammatory agent. At least part of its anti-inflammatory effects seems to be mediated by interfering with pro-inflammatory signalling cascades. The most important of these is the Nuclear Factor-Kappa B (NF-κB) cascade, as it directly activates and transcribes most gene targets that regulate and amplify the inflammatory response (i.e., cytokines, chemokines, apoptotic and phagocytic cells).This raises the possibility that betanin rich beetroot extract could exhibit anti-inflammatory effects to rival synthetic drugs.

Conclusion:

Based on the available data, beetroot extract concludes to be a powerful dietary source of health promoting agents that holds potential as therapeutic treatment for several pathological disorders. The powerful antioxidant, anti-inflammatory and vascular-protective effects offered by beetroot and its constituents have been clearly demonstrated by several in vitro and in vivo human and animal studies; hence its increasing popularity as a nutritional approach to help manage cardiovascular disease and cancer. In the human studies to date, beetroot supplementation has been reported to reduce blood pressure, attenuate inflammation, avert oxidative stress, preserve endothelial function and restore cerebrovascular haemodynamics.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4425174/

It is widely recognized that oxidative stress is implicated in the pathogenesis of hypertension.

Oxidative stress is defined as an excessive production of reactive oxygen species (ROS) that cannot be quenched by antioxidants. Agents that can suppress oxidative stress therefore represent an effective therapeutic option for the management and treatment of hypertension. Overwhelming evidence from in vitro experiments suggests that grape seed extract has an antioxidant property that can protect cells from ROS-mediated DNA damage. This property is mainly determined by polyphenols, especially proanthocyanidins, contained in grape seed extract, which can well interpret the French paradox that refers to the low rate of coronary heart disease mortality in France people despite the diets being rich in saturated fat. Several clinical trials have reported a beneficial impact of grape seed extract on blood pressure.

The key findings in study was that grape seed extract exerted a beneficial impact on blood pressure, and this impact was more obvious in younger or obese subjects, as well as in patients with metabolic disorders.

With accumulation of data from a number of clinical trials, a meta-analysis was undertaken that involved 16 trials and 810 study subjects, findings demonstrated the apparently beneficial impact of grape seed extract on both Systolic BP and Diastolic BP. It is widely recognized that grape seed extract, a polyphenolic compound, contains antioxidants that can help prevent cell damage caused by free radicals. Experimental data have indicated that grape seed extract could lead to an endothelium-dependent relaxation in rabbit aorta.  Moreover, Lopez-Sepulveda et al found that polyphenols in red wine were able to improve endothelial function of large vessels in female spontaneously hypertensive rats by enhancing nitric oxide bioactivity and lowering blood pressure. Further experiments by Wallerath et al suggested that resveratrol, a polyphenolic phytoalexin in red wine, could enhance the expression and activity of endothelial nitric oxide synthase in human umbilical vein endothelial cells, possibly through the activation of PI3K/Akt pathway. These findings potentially contribute to a better understanding of the mechanism of grape seed extract treatment and blood pressure regulation.

Conclusion:

Findings demonstrate that grape seed extract can exert a beneficial impact on blood pressure, and this impact was more obvious in younger or obese subjects, as well in patients with metabolic disorders.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pubmed/18227483

The increased incidence of cardiovascular diseases (CVDs) (atherosclerosis, hypertension, stroke, ischemic heart diseases, heart failure, etc.) will lead to an expected worldwide number of CVD-related deaths of more than 23.6 million by 2030. Resveratrol (RES) is a non-flavonoid polyphenolic compound that is a stilbene derivative. It is a phytoalexin produced by plants, and is notably present in grapes and red wine. It could play a potential protective role against CVDs.

One of the cardioprotective mechanisms of RES is due to its ability to upregulate eNOS, which favours nitric oxide-mediated vasodilation. In vitro experiments under conditions mimicking diabetes, i.e., in the presence of high glucose concentrations, have indirectly shown a potential benefit of RES on endothelial function, by improving the bioavailability of nitric oxide (•NO).

Diabetes is a well-known CV risk factor. It is characterized by a chronic hyperglycaemia, micro- and macrovascular complications including an accelerated atherosclerosis, lipid accumulation in the arterial intima, chronic inflammation and oxidative stress. This is concomitant with an endothelial dysfunction, a proinflammatory phenotype, an intracellular oxidative stress, and consequent perturbations of the •NO pathway. The physiological roles of •NO consist in improving the vasodilation and decreasing platelet aggregation, leukocyte recruitment and proliferation of smooth muscle cells, which is in favour of an inhibition of atherosclerosis formation and progression. RES could exhibit beneficial properties both as an antioxidant and as a regulator of •NO metabolism.

Atherosclerosis predominantly affects the intimal layer of the arterial vessel wall. It is characterized by the deposition of extracellular lipids, the proliferation and migration of local smooth muscle cells, and a chronic inflammation. It leads to luminal narrowing and/or thrombus formation, resulting in clinical events such as coronary artery disease, peripheral arterial disease or stroke. Due to the involvement of lipids, especially low-density lipoproteins (LDLs), in the atherosclerotic process, it could be of interest to improve the lipid profile. Some preclinical studies have shown that RES could modify this profile, notably by decreasing plasma triglyceride and LDL-cholesterol levels, and by increasing HDL-cholesterol. As reported by Cho et al. RES could also potentiate the hypocholesterolemiant action of pravastatin, by down-regulating the 3-hydroxy-3-methyl-glutaryl-CoAreductase (HMG-CoA reductase), an enzyme that intervenes in the first steps of cholesterol biosynthesis. Besides, RES could increase the expression of the LDL receptors (LDL-R) in hepatocytes in vitro, thereby contributing to further decrease blood LDL-cholesterol levels. In addition, the antioxidant properties of RES resulted in a decrease of LDL oxidation (process directly involved in atherogenesis, an induction of several endogenous antioxidant systems, and anti-inflammatory properties. The inhibition of smooth muscle cell migration also participates to the antiatherogenic properties of RES. All these properties show that RES acts on the major factors involved in the atherosclerotic process.

Hypertension constitutes a major risk factor for CVDs. Anti-hypertensive effects of RES have been reported in several animal models of hypertension, after treatment by 10 to 320 mg RES/kg body weight/day, for 14 days to 10 weeks, depending on the studies. It is noteworthy that relatively low doses of RES (5–10 mg/kg/day) significantly lowered blood pressure in animal models associating hypertension with insulin resistance, which could suggest that RES would be more efficient in patients with diabetes or metabolic syndrome. In several studies, RES was administered prior to the development of hypertension. For instance, Dolinsky et al. observed that a high dose of RES attenuated high pressure and prevented cardiac hypertrophy in two hypertensive animal models, namely spontaneously hypertensive rats and angiotensin-II infused mice. A few studies have shown the ability of RES to reverse cardiac hypertrophy and contractile dysfunction, two structural and functional abnormalities associated with hypertension.

Conclusion:

Considering the beneficial effects of RES on hypertension, obesity, inflammation, diabetes and dyslipidemia, RES could constitute an interesting pharmacological approach for the treatment of metabolic syndrome, which is associated with an increased risk of CVD development. Most studies showed effectiveness of RES when it was administered as a pre-treatment.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4882663/

Adequate intake of vitamin K2 has been shown to lower the risk of vascular damage because it activates MGP, which inhibits calcium from depositing in the vessel walls. Hence, calcium is available for multiple other roles in the body, leaving the arteries healthy and flexible.

Vitamin K2 deficiency results in inadequate activation of MGP, which greatly impairs the process of calcium removal and increases the risk of calcification of the blood vessels. Because that calcification occurs in the vessel walls, it leads to thickening of the wall via calcified plaques (i.e., to the typical progression of atherosclerosis), which is associated with a higher risk of cardiovascular events.

A population-based Rotterdam study studied 4807 healthy men and women older than age 55 years, evaluating the relationship between dietary intake of vitamin K2 and aortic calcification, heart disease, and all-cause mortality. The study revealed that high dietary intake of vitamin K2 —at least 32 mcg per day, with no intake of vitamin K1, was associated with a 50% reduction in death from cardiovascular issues related to arterial calcification and a 25% reduction in all-cause mortality.

Those findings were supported by another population-based study with 16 000 healthy women aged 49 to 70 years. After 8 years, the data showed that a high intake of natural vitamin K2 was associated with protection against cardiovascular events. For every 10 mcg of dietary vitamin K2 consumed in the forms of menaquinone 7 (MK-7), menaquinone 8 (MK-8), and menaquinone 9 (MK-9), the risk of coronary heart disease was reduced by 9%. A study on 564 postmenopausal women also revealed that intake of vitamin K2 was associated with decreased coronary calcification.

One recent, double-blind, randomized clinical trial investigated the effects of supplemental MK-7, MenaQ7 (NattoPharma ASA, Hovik, Norway), within a 3-year period for a group of 244 postmenopausal Dutch women. The researchers found that a daily dose of 180 mcg was enough to improve bone mineral density, bone strength, and cardiovascular health.

A study pending publication of 244 postmenopausal women who took supplements with 180 mcg of vitamin K2, as MK-7, for 3 years daily actually showed a significant improvement in cardiovascular health as measured by ultrasound and pulse-wave velocity, which are recognized as standard measurements for cardiovascular health. In that trial, carotid artery distensibility was significantly improved for a 3-year period as compared with that of a placebo group. Also, pulse-wave velocity showed a statistically significantly decrease after 3 years for the vitamin K2 (MK-7) group, but not for the placebo group, demonstrating an increase in the elasticity and reduction in age-related arterial stiffening.

Conclusion:

K2 is linked to many benefits, particularly bone and cardiovascular health. Because diets often fall short of the guidelines, in particular in individuals with higher needs, such as older adults, and postmenopausal women, dietary supplementation can help address the body’s demands. Vitamin K2 promotes arterial flexibility by preventing accumulation of arterial calcium and supplementation with it could correct calcium amounts in the body that are out of balance. Thus, calcium in tandem with vitamin K2 may well be the solution for bringing necessary bone benefits while circumventing an increased risk for heart disease.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4566462/

Vitamin D3 plays a well-recognised role in musculoskeletal health but evidence also suggests a critical role in blood pressure (BP) regulation and vascular health. In vivo and in vitro studies have suggested a number of pathways by which Vitamin D3 could directly benefit the vasculature in addition to acting as a negative regulator of the renin-angiotensin system to influence BP control and modify large artery stiffness. Observational data during the last decade suggest a relationship of low Vitamin D3 levels with cardiovascular end points, including coronary artery disease, myocardial infarction (MI), heart failure (HF), stroke and cardiovascular death. Additionally, more than 4 decades of cross-sectional research generally show a consistent inverse association between Vitamin D3 levels and surrogate cardiovascular markers of BP, large artery stiffness, atherosclerotic burden and endothelial function.

Vitamin D3 deficiency has been associated with an increased risk of death, HF, MI or stroke in healthy postmenopausal women, as well as with an increased risk of sudden cardiac death or fatal or non-fatal stroke, non-fatal MI and death related to other heart diseases among diabetic patients with chronic kidney disease (CKD). In a small study of patients with acute coronary syndrome, Vitamin D3 deficiency was also independently associated with in-hospital cardiovascular death. In general population studies, low Vitamin D3 levels were associated with an increased incidence of coronary artery disease, MI, HF, stroke and all-cause death as well as increased cardiovascular death. Several other studies have demonstrated an increased risk of cardiovascular death associated with low Vitamin D3 levels among different patient groups including HF outpatients (in a small study), patients with metabolic syndrome and cardiovascular symptoms, and patients with chronic obstructive pulmonary disease. Furthermore, data extracted from medical records of 126 men with moderate CKD and Vitamin D3 deficiency showed that Vitamin D3 treatment was associated with decreased cardiovascular events. In this study, the treatment group was defined based on an increase in serum Vitamin D3 levels by 25% from baseline within 6 months, whilst the remaining patients were considered as controls. The risk of cardiovascular death was also lower among haemodialysis patients regularly using Vitamin D3 supplements in a Japanese hospital. Overall, these data suggest fairly consistently that low Vitamin D3 levels are associated with an increased risk of cardiovascular events, including death; in addition, the data hint towards the potential for Vitamin D3 supplementation possibly reversing the adverse cardiovascular effects of low Vitamin D3.

Brachial BP, large artery stiffness (as measured by carotid-to-femoral pulse wave velocity, an estimate of aortic pulse wave velocity and the current “gold standard” measure of large artery stiffness) and central hemodynamic parameters (such as augmentation index, a marker of central systolic loading) are independent predictors of cardiovascular risk. Many observational studies have reported an inverse association between low Vitamin D3 levels and brachial BP in large samples from the general population, but also among Peruvian adolescents, middle-aged individuals, people aged >60 years and the elderly, pregnant women and women aged 20-80 years. Other markers of regional arterial stiffness, including increased carotid-radial pulse wave velocity and brachial-ankle pulse wave velocity, have been associated with lower Vitamin D3 levels among people with type 2 diabetes mellitus. In summary, observational evidence is consistently and strongly supportive of an association between Vitamin D3, BP and vascular health.

Strong relationships have also been observed between Vitamin D3 level, atherosclerotic burden and endothelial function markers. Carotid intima medial thickness, a marker of large artery atherosclerosis, known to be predictive of cardiovascular events, was found to be inversely associated with low Vitamin D3 levels among different populations, including apparently healthy, predominantly white older individuals, relatively healthy Chinese women and patients with peripheral arterial disease.

Conclusion:

Vitamin D deficiency is a highly prevalent condition and is independently associated with most CVD risk factors and to CVD morbidity and mortality.

REFERENCE SOURCE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290441/

Citrulline and arginine scientific studies

A study in humans showed the citrulline supplementation’s “time release” effect on arginine production. In this study an oral dose of 1 gram of citrulline resulted in a 227% peak increase in plasma arginine levels after 4 hours, compared with a 90% peak increase with the same dose of arginine.

Oral administration of citrulline alongside arginine appears to be considerably more efficient at raising plasma levels of arginine over the long term than arginine by itself.

Reduces blood pressure

L-Arginine and L-Citrulline supplementation combination has shown to reduce blood pressure in 17 young (average age 21.6 years) men with normal blood pressure after they were submitted to a cold pressor test (CPT). (A cold pressor test is a cardiovascular test done by having the subject immerse his hand into a bucket of ice water for one minute. Blood pressure and heart rate are then evaluated). The men were randomly assigned to four weeks of oral citrulline and arginine supplementation or placebo in a crossover design. Blood pressure was measured after the blood pressor test.

The results showed that compared to placebo, oral citrulline and arginine decreased brachial systolic blood pressure (-6 +/- 11 mm Hg), aortic systolic blood pressure (-4 +/- 10 mm Hg), and aortic pulse pressure (-3 +/- 6 mm Hg) during CPT.

Even more importantly, new studies are showing that supplemental citrulline also assists in nitric oxide production by boosting blood levels of arginine.

A study published in the journal of sports and science medicine has found that vitamin C combined with arginine increases NO levels more than just arginine alone. Supposedly, vitamin C destroys free radicals that break down nitric oxide.

OBJECTIVE According to the literature L- Arginine supplementation improves physical performance by decreasing fatigue due to nitric oxide (NO) vasodilatation effect. This investigation sought to assess the effect of L-Arginine supplementation on strength and body composition of young soccer players during an 8-week weight training protocol.

METHODS 20 soccer players, age between 17 and 19 years old (mean 17.65 ± 0.8 yrs. were supplemented either with 3 g of L-arginine plus 1 g of vitamin C (group ARG) or just with 1 g of vitamin C (group CON). They underwent eight weeks of weight training (3 times/ week). Statistical analyses used were ANOVA and "t" test.

RESULTS Group ARG showed a significant increase in body-weight (66.4 ± 6.1; 67.84 ± 6.8 kg), lean body mass (60.38 ± 6.05; 62.07± 5.9 kg) and muscular strength of both legs, right(R) and left(L) (Extension R 184.8 ± 17.4 to 195.8 ± 16.3; L 191.1 ± 18.4 to 199.1 ± 19.1), and a decrease in body fat (6.02 ± 0.6 - 5.77 ± 0.59 Kg) and %body fat (9.45 ± 0.8 to 8.66 ± 0.77) (p<0.05). There was no significant change in CON group.