The amino acid arginine has been shown to affect the growth of several tumours, although the mechanisms of its action are not clear. In the present study, using a human breast tumour cell line (MCF-7), we investigated the arginine requirements of tumour cells for optimal protein synthesis and growth, and the metabolic pathway responsible for the arginine-dependent growth. The results showed that MCF-7 cells are highly dependent on arginine for growth and that the requirement for arginine is much higher than for an indispensable amino acid, leucine, indicating that arginine is needed for pathways other than protein synthesis. In arginine-free cultures, growth could be completely restored by the urea cycle intermediate citrulline. However, arginine could not be replaced by the urea cycle intermediate and the direct precursor for polyamine synthesis, ornithine, or by the polyamine putrescine, suggesting that the high dependence on arginine is not due to a requirement for polyamine synthesis. Moreover, inhibition of NOS [NO (nitric oxide) synthase] did not affect cell protein synthesis and growth, and the arginine analogue and substrate for NOS, homoarginine, could not replace arginine, implying that the conversion of arginine into NO is not involved in the growth-promoting effects of arginine. The major determinant for the high dependence of MCF-7 cells for arginine was found to be the irreversible conversion of this amino acid into ornithine by the intracellular enzyme arginase. The conversion into ornithine caused a progressive depletion of arginine from the culture medium, which ultimately inhibited cell protein synthesis and halted growth. Intracellular arginase activity may be the major factor determining the requirement for arginine of all cells in culture.

Acute inflammation impairs vascular function. Based on the association between endothelial dysfunction and plasma concentrations of L -arginine and the endogenous nitric oxide synthase inhibitor ADMA (asymmetrical dimethylarginine), we hypothesized that the ratio between L -arginine and ADMA could be affected by experimental inflammation. Plasma concentrations of L -arginine, ADMA and SDMA (symmetrical dimethylarginine) were studied at baseline and 3.5 h after intravenous administration of Escherichia coli endotoxin [LPS (lipopolysaccharide), 20 units/kg of body mass; n =8] or placebo ( n =9) in healthy males. L -Arginine and dimethylarginines were quantified after solid-phase extraction by reversed-phase HPLC. Body temperature, heart rate and leucocyte count increased after LPS administration ( P <0.01 for all). LPS administration decreased plasma concentrations of L -arginine from 66 µmol/l [95% CI (confidence interval): 56, 88] at baseline to 48 µmol/l (CI: 40, 60) after 3.5 h ( P <0.02), but did not affect ADMA and SDMA concentrations. Consequently, the L -arginine/ADMA ratio declined significantly from a median of 159 (CI: 137, 193) to 135 (CI: 103, 146); a decrease of 25 (CI: -68, -13; P <0.02). L -Arginine, ADMA, SDMA and the L -arginine/ADMA ratio remained constant over time in controls. Acute inflammation reduces the L -arginine/ADMA ratio which could contribute to impaired vascular function.

The role of the L -arginine/nitric oxide (NO) pathway in myocardial ischaemic/reperfusion injury remains controversial in experimental animal models. The aim of the present studies was to investigate the role of this pathway in the human myocardium. Myocardial specimens from right atrial appendages of patients undergoing elective coronary bypass graft surgery were incubated in crystalloid buffer at 37 °C and subjected to 120 min of simulated ischaemia followed by 120 min of reoxygenation. Tested drugs were added 15 min before ischaemia, and maintained during ischaemia and throughout reoxygenation. Ischaemia resulted in severe myocardial damage, as assessed by the leakage of lactate dehydrogenase (LDH) into the incubation medium and by the capacity of the tissue to reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to formazan product. L -Arginine (10 mM), a precursor of NO, significantly decreased LDH leakage (from 9.0±0.6 to 5.3±0.3 units/g wet wt; P < 0.05), but had no effect on MTT reduction or oxygen consumption. D -Arginine (10 mM), N G -nitro- L -arginine methyl ester ( L -NAME; 0.5 mM), an NO synthase inhibitor, and S -nitroso- N -acetylpenicillamine (at 1, 100, 500 and 1000 µ M), an NO donor, had no significant effects on the measured indices, and L -NAME did not reverse the protection afforded by L -arginine against LDH leakage. In addition, the formation of nitrotyrosine was not influenced by ischaemia/reoxygenation alone or by the agents investigated. In conclusion, these data suggest that L -arginine affords modest protection against ischaemic/reoxygenation injury of the human myocardium, an action that is NO-independent, and that NO metabolism does not play a significant role in this model.

Systemic administration of L -arginine alters renal haemodynamics in humans. We examined whether L -arginine-induced vasodilation of the renal vasculature is related to an increased production and release of NO by comparing the effects of L - and D -arginine on renal endothelium-dependent vasodilation. In a double-blind randomized cross-over study including 20 young, healthy male white subjects (age 26±2 years), we determined the effects of intravenous administration of L -arginine or its enantiomer D -arginine, at doses of 100 mg/kg body weight for 30 min or 500 mg/kg for 30 min, on renal haemodynamics. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were assessed by a constant-infusion input-clearance technique (using p -aminohippuric acid and inulin respectively). In addition, changes in blood pressure, heart rate, urinary sodium excretion (U Na ) and urinary cGMP were measured. HPLC was used to determine L - and D -arginine concentrations. Intravenous infusion of L -arginine at 100 mg/kg for 30 min increased RPF from 641±87 to 677±98 ml/min ( P = 0.019), whereas infusion of D -arginine did not (from 642±74 to 657±86 ml/min; not significant). The change in RPF was more marked during the infusion of L -arginine than during the infusion of D -arginine (+36±61 versus +16±57 ml/min; P = 0.037). Infusion of both L - and D -arginine at doses of 500 mg/kg for 30 min increased RPF from baseline [from 641±87 to 762±133 ml/min ( P < 0.001) and from 642±74 to 713±120 ml/min ( P = 0.004) respectively], but the change in RPF again was greater in response to L -arginine infusion than to infusion with D -arginine (+121±97 versus +71±94 ml/min; P = 0.018). In accordance, changes in renal vascular resistance (RVR) were higher in response to L -arginine compared with D -arginine for both doses ( P < 0.05 and P < 0.001 respectively). U Na increased only with L -arginine (change in U Na , +0.33±0.26 mmol/min; P < 0.01) but not with D -arginine (change in U Na , +0.11±0.17 mmol/min; not significant). The change in U Na was more pronounced during infusion of L -arginine compared with infusion of D -arginine ( P = 0.023). In parallel, urinary excretion of cGMP only increased in response to L -arginine (+676±272 pmol/l; P = 0.038) and not during D -arginine infusion (+185±153 pmol/l; not significant). L -Arginine-induced changes in RPF, RVR, U Na and cGMP excretion differed significantly from those induced by D -arginine. Thus although no direct measurements of NO synthesis were performed, putative markers of NO synthesis suggest that the renal vasodilatory response to L -arginine, at least in part, was due to increased production and release of NO. The dose of L -arginine at 100 mg/kg for 30 min emerged as the most suitable, because of the absence of systemic haemodynamic changes. The effects of infusion of L -arginine at 500 mg/kg for 30 min on renal endothelium-dependent vasodilation need to be corrected for the effects of D -arginine before conclusions can be drawn.

Acute administration of L -arginine, the precursor of endothelial nitric oxide, has been shown to improve endothelial function in hypercholesterolaemic rabbits and humans. Animal studies suggest that this beneficial effect, which is thought to be related to the increased availability of nitric oxide, may not be sustained during chronic oral administration. Pharmacokinetic alterations may contribute to this observation. The present study was designed to examine the disposition of L -arginine in hypercholesterolaemic subjects during long-term administration. Plasma L -arginine concentrations were determined by HPLC in 10 patients (eight women and two men; mean age 46±16 years) after an intravenous dose of 10 or 30 g and an oral dose of 5 or 7 g. Pharmacokinetic studies were performed at regular intervals (4 weeks) during a 12-week period of oral L -arginine administration (14–21 g/day). The average plasma L -arginine concentrations before (baseline) and during administration were 16.1±1.2 and 22.5±1.3 μ g/ml respectively ( P < 0.05). Plasma concentrations of L -arginine remained above baseline throughout weeks 2–12. The L -arginine exposure, expressed as a normalized area-under-the-curve for 8 h (AUC 0–8 ) after oral or intravenous doses during the first visit, was 894.4±118.7 and 1837.8±157.0 units respectively. There were no significant changes in peak plasma L -arginine concentrations or in the AUC 0–8 after oral and intravenous doses during subsequent visits ( P > 0.05). The mean non-renal clearance of L -arginine during the four visits remained constant. Knowledge of the pharmacokinetics of L -arginine may be useful in the design of clinical trials involving this agent, as well as in the interpretation of the pharmacodynamics of this important precursor of nitric oxide.

1. This study examined the effects of altering nitric oxide levels with sodium nitroprusside or l -arginine in rat hearts stored hypothermically. 2. Hearts were microperfused at 4 ;°C for 24 ;h with a modified Krebs–Henseleit buffer (KHB) that contained either sodium nitroprusside, l -arginine, l -arginine methyl ester or dexamethasone. 3. After hypothermic storage, hearts were rewarmed to 37 ;°C with KHB alone or KHB containing sodium nitroprusside or l -arginine. Cardiac function was then assessed in either Langendorff mode or working heart mode. 4. Compared with values from fresh unstored hearts, hypothermic stored hearts showed a significant decrease in coronary flow and left ventricular developed pressure when the stored hearts were perfused in Langendorff mode. These hearts also produced less aortic flow and cardiac output when perfused in the working mode. 5. Hearts hypothermically microperfused with buffer containing either l -arginine or sodium nitroprusside and then reperfused in the Langendorff mode with untreated KHB buffer had the highest left ventricular developed pressure and coronary flow values. Aortic flow and cardiac output were also higher in these hearts. 6. In all groups of stored hearts, the concentrations of both ATP and creatine phosphate were significantly low, when compared with values from freshly isolated hearts. Addition of dexamethasone to the buffer either during storage or during reperfusion had no beneficial effect on high-energy phosphate loss or cardiac performance of stored hearts. 7. This study showed that the addition of nitric oxide donors to storage buffer significantly improves cardiac function on normothermic reperfusion. The improved functional recovery is unrelated to the high-energy phosphate content of these hearts.

1. Endothelium-derived nitric oxide (NO) contributes to the regulation of vascular tone and blood pressure. Infusion of l-arginine produces systemic vasodilatation via stimulation of endogenous NO formation. Vasodilatation is accompanied by an increase in peripheral arterial blood flow. However, it is not known whether capillary nutritive blood flow increases as well. The time course and dose-response pattern of this effect remain to be elucidated. 2. Two groups of ten patients with peripheral vascular disease (PVD) received an intravenous infusion of 8 g or 30 g of l-arginine over a period of 40 min. Blood pressure and heart rate were monitored non-invasively. Muscular blood flow (MBF) of the calf was determined at 0, 20, 40, 60, 80 min by positron emission tomography with H 2 15 O as flow tracer. Plasma l-arginine and cyclic GMP (cGMP) levels were determined at the same time points. 3. l-arginine induced a dose-related decrease in blood pressure during the infusion period. MBF and plasma cGMP levels during and after the infusion of 8 g of l-arginine did not change significantly. In the patients receiving 30 g of l-arginine, MBF was enhanced significantly from 1.56 ± 0.14 to 2.09 ± 0.21 ml min −1 100 ml −1 at 40 min and 2.23 ± 0.15 ml min −1 100 ml −1 after 80 min (+43.0%). The increase in MBF was paralleled by an increase in plasma cGMP from 4789.8 ± 392.2 nmol/l at baseline to 9223.2 ± 1233.6 nmol/l at 40 min. 4. We conclude that intravenous l-arginine enhances nutritive capillary MBF in patients with PVD via the NO—cGMP pathway in a dose-related manner. This effect might be therapeutically beneficial in patients with PVD.

1. Pharmacological stimulation of the synthesis of nitric oxide (NO) may be important in the prevention or treatment of cardiovascular diseases. 2. There is much discussion as to whether the precursor of NO, l-arginine, is able to stimulate basal endothelial NO production. l-Arginine is known to have vasodilating effects. However, it is not clear whether l-arginine-induced vasodilatation is attributable to an increase in NO production or to other systemic effects of l-arginine. 3. To investigate further the mechanisms of the l-arginine-induced vasodilatation, we compared the responses to l-arginine with those to saline and l-lysine in healthy subjects. l-Lysine is not a substrate for NO synthesis, but shares many of l-arginine's other properties. 4. During l-arginine infusion, blood pressure decreased [systolic blood pressure from 120.2 (SD 8.8) to 117.3 (12.1) mmHg ( P = 0.05); diastolic blood pressure from 65.3 (5.9) to 61.6 (7.9) mmHg ( P < 0.01)], and heart rate and extracellular fluid volume increased. The total peripheral vascular resistance decreased during l-arginine infusion by 18.0 (11.4)% ( P ≤ 0.05 compared with baseline and compared with l-lysine infusion). These results indicate vasodilatation. No changes were observed during l-lysine and saline infusion. 5. Plasma cyclic GMP (the second messenger for NO) increased during l-arginine but also during l-lysine infusion [from 5.7 (1.2) to 6.8 (1.7) nmol/l ( P < 0.01), and from 5.8 (1.8) to 7.0 (2.9) nmol/l ( P < 0.05) respectively]. Plasma l-citrulline (a by-product of NO synthesis from l-arginine) increased during l-arginine infusion from 30.6 (7.5) to 47.1 (9.9) μmol/l ( P < 0.001), but also during l-lysine infusion from 32.7 (6.5) to 42.0 (8.3) μmol/l ( P < 0.001). 6. Plasma electrolytes and atrial natriuretic peptide concentrations responded similarly to l-arginine and l-lysine infusion, indicating similar effects on osmolality, plasma volume expansion and potassium distribution. 7. In conclusion, although l-lysine infusion had effects that were similar to those of l-arginine infusion, no vasodilatation was observed. Therefore, these effects cannot account for the l-arginine-induced vasodilatation. This finding indirectly supports the hypothesis that the vasodilatation during l-arginine infusion might be mediated by an increase in NO synthesis. If so, our data suggest that the presumed markers for NO synthesis, plasma cyclic GMP and l-citrulline concentrations, do not accurately reflect this increase. Instead, the rise in plasma cyclic GMP may be related to the rise in ANP. The rise in l-citrulline may be related to competition with l-arginine for the same cell membrane transport mechanism and to stimulation of the urea cycle.

1. It has been shown in animals that substance P as well as acetylcholine releases endothelium-derived nitric oxide and evokes vasodilatation and that ATP-induced vasodilatation is partially mediated by nitric oxide. The aim of this study was to examine whether vasodilator effects of substance P and ATP are mediated by nitric oxide in humans. 2. In healthy volunteers ( n = 35), we measured forearm blood flow by a strain-gauge plethysmograph while infusing graded doses of acetylcholine, substance P, ATP or sodium nitroprusside into the brachial artery before and after infusion of N G -monomethyl- l -arginine (4 or 8 μmol/min for 5 min). In addition, we measured forearm blood flow while infusing substance P before and during infusion of l -arginine (10 mg/min, simultaneously), or before and 1 h after oral administration of indomethacin (75 mg). 3. Acetylcholine, substance P, ATP or sodium nitroprusside increased forearm blood flow in a dose-dependent manner. N G -Monomethyl- l -arginine decreased basal forearm blood flow and inhibited acetylcholine-induced vasodilatation but did not affect substance P-, ATP-, or sodium nitroprusside-induced vasodilatation. Neither supplementation of l -arginine nor pretreatment with indomethacin affected substance P-induced vasodilatation. 4. Our results suggest that, in the human forearm vessels, substance P-induced vasodilatation may not be mediated by either nitric oxide or prostaglandins and that ATP-induced vasodilatation may also not be mediated by nitric oxide.

1. The present study was performed to determine the relationship between diabetic glomerular hyperfiltration and nitic oxide as modulated by the chronic administration of l-arginine and/or N -ω-nitro-l-arginine, a known nitric oxide synthase inhibitor in streptozotocin-induced diabetic rats. 2. Normal rats and rats drinking hypertonic glucose (10%) were used as time-controlled groups. Six weeks after administration of streptozotocin the diabetic rats had significantly higher creatinine clearance (667 ± 53 μl min −1 100 g −1 body weight) than before and streptozotocin (456 ± 38 μl min −1 100 g −1 body weight, P <0.005) and very high plasma (37.8 ± 10.9 μmol/l) and urinary (3.492 ± 0.179 nmol min −1 100 g −1 body weight) nitrite + nitrate (stable metabolites of nitric oxide) values compared with before streptozotocin administration [19.3 ± 2.8 μmol/l ( P <0.001) and 0.420 ± 0.051 nmol min −1 100 g −1 body weight ( P <0.001) respectively]. The 6-week diabetic rats had higher systolic blood pressure (124.2 ± 2.9 mm Hg, P <0.05) than before streptozotocin (108 ± 8 mmHg), but had a value similar to that of the hypertonic-glucose-drinking rats. 3. The diabetic rats supplemented with l-arginine did not show an increase in creatinine clearance and had a lower urinary excretion of nitrite + nitrate (0.999 ± 0.27 nmol min −1 100 g −1 body weight, P <0.005) than the respective untreated streptozotocin-induced diabetic rats. Creatinine clearance increased in the normal and glucose-drinking rats that received l-arginine. The administration of l-arginine resulted in significant reduction in blood pressure in all groups studied. The chronic nitric oxide synthase inhibitor resulted in high blood pressure, and in a significant decrease in creatinine clearance and urinary nitrite + nitrate excretion in all groups studied. In both diabetic and glucose-drinking rats, the l-arginine therapy resulted in significantly lower plasma and urinary glucose levels than in their respective untreated control groups. 4. The nitric oxide synthase inhibitor increased the plasma and urinary glucose concentration in both diabetic and glucose-drinking rats. 5. Our results indicate that diabetic rats are characterized by high plasma concentrations and elevated urinary excretion of nitrite + nitrate, suggesting a state of high nitric oxide production. The vascular response to nitric oxide in diabetic rats may be different at the glomerular and peripheral vascular bed.

1. Endogenous nitric oxide plays an important physiological role and is synthesized by several isoforms of nitric oxide synthase from the semiessential amino acid l-arginine. Nitric oxide is detectable in the exhaled air of normal individuals and may be used to monitor the formation of nitric oxide in the respiratory tract. 2. We have investigated the effect of orally administered l-arginine (0.05, 0.1, 0.2 g/kg) compared with matched placebo on the concentration of nitric oxide in the exhaled air in 23 normal individuals. 3. l-Arginine caused significant increases in the concentration of nitric oxide in exhaled air at doses of 0.1 and 0.2 mg/kg, which was maximal 2 h after administration. This was associated with an increase in the concentration of l-arginine and nitrate in plasma. There were no significant changes in heart rate, blood pressure or forced expiratory volume in 1 s. 4. These results suggest that an increase in the amount of substrate for nitric oxide synthase can increase the formation of endogenous nitric oxide. This may have therapeutic relevance in diseases in which there is defective production of nitric oxide.

1. L-Arginine is the physiological precursor of nitric oxide which induces vasodilatation and inhibits platelet aggregation by the formation of cyclic GMP. 2. In the present study we investigated the effects of an intravenous infusion of L-arginine (30 g, 30 min) compared with placebo on blood pressure, heart rate and peripheral haemodynamics in ten healthy male subjects. Cyclic GMP, NO − 2 and NO − 3 were determined in plasma and urine to assess NO production in vivo by a new, highly specific and sensitive gas chromatography-mass spectrometry method. 3. L-Arginine significantly decreased mean arterial blood pressure and increased heart rate. The effect was more pronounced on diastolic than on systolic blood pressure. This was due to a decreased peripheral arteriolar resistance, as in femoral artery Doppler sonography the arterial diameter was unchanged but blood flow was increased. These haemodynamic effects were not observed after placebo administration. 4. Urinary excretion of cyclic GMP increased by 65.4% after L-arginine and by 25.1% after placebo. Urinary NO − 2 excretion was near the threshold of detection. Urinary NO − 3 excretion increased by 79.7% after L-arginine. Plasma arginine levels increased nearly ten-fold after the L-arginine infusion, and plasma cyclic GMP increased by a similar rate as in urine. However, plasma NO − 2 and NO − 3 remained unchanged after both treatments, as did plasma α-atrial natriuretic peptide levels. 5. Platelet aggregation was inhibited by 32.7% after L-arginine ( P < 0.05), but was unchanged after placebo. Platelet intracellular cyclic GMP was increased by 43.0% after L-arginine, but not after placebo ( P < 0.05). 6. We conclude that intravenous L-arginine decreases peripheral arteriolar tone and inhibits platelet aggregation in healthy human subjects by enhancing nitric oxide formation and, concomitantly, cyclic GMP formation.

1. Uncomplicated insulin-dependent diabetes mellitus is associated with generalized vasodilatation. This vasodilatation is believed to contribute to the development of microvascular complications. The endothelium plays an important role in the regulation of vascular tone. 2. To investigate the role of endothelial mediators, we measured plasma endothelin levels and studied the vascular effects of intravenous l-arginine (the precursor of NO) in 10 male type 1 diabetic patients and 10 non-diabetic subjects. 3. The baseline plasma endothelin level was significantly lower in the diabetic patients [mean 1.7 (SD 0.5) versus 2.1 (0.4) pmol/l; P < 0.05] than in the control subjects. 4. During l-arginine infusion, plasma cyclic GMP (the second messenger for NO) increased in the control subjects [from 5.1 (2.9) to 6.9 (2.9) nmol/l; P < 0.05 versus saline] and in the diabetic patients [from 4.6 (1.8) to 5.7 (2.2) nmol/l; P = 0.09]. l-Citrulline (a by-product of NO synthesis from l-arginine) increased in both groups. The responses to l-arginine were not significantly different between the control subjects and the diabetic patients. The plasma atrial natriuretic peptide level did not change in either group during infusion of l-arginine or of an equal volume of isotonic saline. 5. Blood pressure decreased slightly during l-arginine administration in both groups. In control subjects, the extracellular fluid volume in the lower leg increased during l-arginine infusion as compared with saline; in the diabetic patients both l-arginine and saline increased the extracellular fluid volume. 6. In conclusion, the vascular effects of l-arginine are similar in men with uncomplicated insulin-dependent diabetes mellitus and in control subjects. Whether these effects are due to an increase in NO synthesis remains unclear. The increase in extracellular fluid volume during saline infusion in diabetic patients suggests an increase in microvascular permeability in

1. We have used an isolated, buffer-perfused, rabbit ear model of acute arterial occlusion to investigate the effects of exogenous l-arginine on the severe impairment of collateral perfusion associated with dietary-induced hypercholesterolaemia. The effects of l-arginine on hypercholesterolaemia-related impairment of endothelium-dependent relaxations to acetylcholine were also investigated in unligated, isolated rabbit ears perfused with buffer. 2. Cholesterol feeding for 8 weeks (blood cholesterol level 66.5 ± 5.3 versus 1.4 ± 0.2 mmol/l, P < 0.001) was associated with almost complete impairment of collateral perfusion, an effect previously observed after inhibition of nitric oxide synthesis. The impairment of collateral perfusion found in hypercholesterolaemia was completely reversed by the addition of 10 mmol/l l-arginine to the perfusion fluid. In control preparations from rabbits fed a normal diet, the addition of 10 mmol/l l-arginine did not influence collateral perfusion. 3. Endothelium-dependent relaxation to acetylcholine was impaired in preparations from the rabbits fed the high cholesterol diet for 8 weeks: the maximum relaxation of tone was 24.6 ± 0.8% and was significantly ( P < 0.01) less than that in the controls (70.3 ± 2.4%). Addition of l-arginine to the perfusion fluid caused a modest improvement in the endothelium-dependent relaxations to acetylcholine, with a maximum response of 43.2 ± 1.3%. 4. We conclude that nitric oxide-dependent collateral perfusion is severely impaired in hypercholesterolaemia and that the addition of exogenous l-arginine fully reverses these changes. Endothelium-dependent relaxations to acetylcholine are similarly impaired by hypercholesterolaemia; however, this deficit was only partially reversed by l-arginine. In the context of collateral perfusion, l-arginine treatment may represent a therapeutic strategy to limit the deleterious effects of hypercholesterolaemia on acute arterial occlusion.

1. The amino acid L-arginine has been shown to enhance immune mechanisms and inhibit tumour growth in experimental animals, but although many of the immunological effects of arginine have been reproduced in man there have been few studies of its effects on human tumours. In this study the effects of arginine on human breast cancers were determined by measuring tumour protein synthesis and comparing this with immunohistochemical assessments of cell proliferation. 2. Patients with breast cancer were randomized to receive either a standard diet or arginine supplementation. At the time of surgery, the rate of tumour protein synthesis was measured by the incorporation of the stable isotope [1- 13 C]leucine into tumour protein. Tumours were also assessed histologically and by staining for the presence of the activation antigen Ki67. 3. The median rate of tumour protein synthesis was 10%/ day (range 5.5–15.8%/day) in the control patients and 25.6%/day (range 9-37%/day) in the patients receiving arginine supplements ( P < 0.005, Wilcoxon rank sum test). The rates of protein synthesis correlated with Ki67 expression within these tumours ( r =0.78, P < 0.001). A double-staining technique confirmed that tumour cells, rather than tumour-infiltrating lymphoreticular cells, expressed Ki67. 4. This study demonstrates that, in contrast to animal studies, L-arginine stimulates human tumours in vivo. This represents the first direct evidence that a single amino acid can modulate the behaviour of a human cancer.

1. The effects of l -arginine on systemic and renal haemodynamics were investigated in conscious dogs. l -Arginine was administered intravenously at doses of 15 and 75 μmol min −1 kg −1 for 20 min. 2. Mean arterial blood pressure, heart rate and cardiac output were not changed significantly by l -arginine infusion. However, l -arginine infusion induced a significant elevation of renal blood flow from 50 ± 3 to 94 ± 12 ml/min (means ± sem , P < 0.01). 3. Simultaneous infusion of N G -monomethyl- l -arginine (0.5 μmol min −1 kg −1 ) significantly inhibited the increase in renal blood flow produced by l -arginine (15 μmol min −1 kg −1 ) without significant changes in mean arterial blood pressure or heart rate. 4. Pretreatment with atropine completely inhibited the l -arginine-induced increase in renal blood flow, whereas pretreatment with indomethacin attenuated it (63 ± 4 versus 82 ± 10 ml/min, P < 0.05). 5. A continuous infusion of l -arginine increased renal blood flow in the intact kidney (55 ± 3 versus 85 ± 9 ml/min, P < 0.05), but not in the contralateral denervated kidney (58 ± 3 versus 56 ± 4 ml/min, P > 0.05). 6. These results suggest that intravenously administered l -arginine produces an elevation of renal blood flow, which may be mediated by facilitation of endogenous acetylcholine-induced release of endothelium-derived relaxing factor and vasodilatory prostaglandins.

1. The direct effects of individual amino acids, including glycine (a neutral amino acid), l-glutamic acid (an acidic amino acid), l-leucine (a neutral, branched-chain amino acid) and l-arginine (a basic amino acid), on renal function were compared with a mixed amino acid solution by using the isolated rat kidney perfused with a physiological saline solution containing 6.7% (w/v) albumin and a basal level of 2 mmol/l mixed amino acids. 2. In a control series, the renal perfusate flow was stable but the glomerular filtration rate, as measured by [ 14 C]inulin clearance, declined with time. A stable glomerular filtration rate could be obtained by increasing the basal perfusate amino acid concentration to 14 mmol/l. 3. The addition of 6 mmol/l mixed amino acids produced a sustained increase in renal perfusate flow and an increase in [ 14 C]inulin clearance, reversing its time-dependent fall. Sodium reabsorption was enhanced, but, unlike the control series, no increase in fractional albumin excretion was obtained. 4. Renal perfusate flow was increased by glycine (6 mmol/l), l-arginine hydrochloride (6 mmoll) and sodium glutamate (6 mmol/l) but remained unaffected by l-leucine. The vasodilatation induced by l-arginine hydrochloride and sodium glutamate was not sustained. 5. The time-dependent fall in [ 14 C]inulin clearance was prevented by glycine, l-arginine and glutamic acid, but not by l-leucine. l-Arginine hydrochloride, like the mixed amino acid solution, produced a significant increase in [ 14 C]inulin clearance. 6. The fractional reabsorption of sodium was increased by glycine and l-leucine, was unaffected by sodium glutamate and was decreased by l-arginine hydrochloride. The time-dependent fall in the fractional excretion of albumin seen in the control series was, however, reversed by all individual amino acids. 7. The results indicate that amino acids can produce renal vasodilatation and hyperfiltration by a direct effect on the kidney, independent of the release of systemic hormones. Individual amino acids, however, differ in their contribution to the response elicited by a mixed amino acid solution. The use of individual amino acids to mimic the renal response to dietary protein in vivo may therefore be inappropriate.

1. The contraction and relaxation responses to the polyoxyethylated vehicles currently used for the intravenous and oral administration of cyclosporin A in allograft recipients were studied in isolated rat aorta. The results were compared with those obtained with commercially available cyclosporin A for intravenous administration. 2. None of these compounds affected resting tension, noradrenaline-induced contraction or endothelium-independent relaxation produced by sodium nitroprusside or bumetanide. However, they all reversed the relaxation induced by acetylcholine, carbamylcholine or adenosine 5′-triphosphate, by a factor of approximately 66%. 3. This reversal of relaxation was unaffected by indomethacin and did not require the presence of cyclosporin A in the vehicles, and was completely abolished by l-arginine (3 × 10 −-5 mol/l). 4. It is concluded that vehicles used for commercial preparations of cyclosporin A interfere with the synthesis of endothelium-derived relaxing factor at an early stage during which l-arginine is made available for enzymatic degradation.