Supplemental oxygen does not modulate responses to acetylcholine or ascorbic acid in the forearm of patients with congestive heart failure.

Despite providing symptomatic relief in patients with congestive heart failure (CHF), supplemental oxygen (O(2)) has been demonstrated to increase total peripheral resistance. The present study investigated the possibility that O(2) inhalation reduces nitric oxide (NO) bioavailability, using endothelium-dependent (acetylcholine) and -independent (phentolamine) vasodilators, and the antioxidant ascorbic acid. Ten patients (nine male and one female) with primary left ventricular failure participated in the study. Forearm venous occlusion plethysmography was used to study blood flow responses to acetylcholine and the alpha-adrenergic antagonist phentolamine during inhalation of either room air or 100% O(2), with and without the simultaneous infusion of ascorbic acid. Neither O(2) inhalation (3.9+/-0.4 compared with 3.8+/-0.3 ml.min(-1).100 ml(-1)) nor ascorbic acid infusion (5.2+/-0.4 compared with 5.5+/-0.4 ml.min(-1).100 ml(-1)) affected resting forearm blood flow. The percentage increase from basal blood flow after acetylcholine infusion was not altered by either O(2) inhalation or ascorbic acid infusion (room air, 140+/-55%; O(2), 118+/-46%; ascorbic acid, 147+/-39%; ascorbic acid+O(2), 109+/-31%). O(2) inhalation did, however, reduce the dilation induced by phentolamine (room air, 131+/-24%; O(2), 80+/-14%; P<0.05). These data indicate that oxygen inhalation does not increase forearm vascular resistance. Secondly, preservation of reactivity to acetylcholine during O(2) inhalation suggests that degradation of NO by O(2)-derived free radicals is not enhanced. Attenuation of phentolamine-induced vasodilation during O(2) inhalation, however, implies increased adrenergic activity, which may possibly exacerbate the detrimental effects of elevated sympathetic activity in CHF.

Modulation of vascular function by diet and exercise.

Clinical research is conducted in free living individuals who are always subject to the influences on vascular function and the major cardiovascular regulators of their lifestyle. The purpose of this paper is to review some lifestyle influences on cardiovascular function, particularly the sympathetic nervous system and endothelially mediated vasodilatation. There are highly differentiated sympathetic responses to feeding, and to acute exercise. Over a longer period obesity has a typical pattern of sympathetic activity. Reduced dietary salt intake elicits profound localised increases in sympathetic activity to the kidney. Marine oil supplementation attenuates the sympathetic responses to psychological stress and improves endothelially mediated vasodilatation in hypercholesterolaemics. Exercise training reduced total noradrenaline spillover, the major beds affected being the renal and skeletal muscle. These examples illustrate the dynamic nature of vascular dilatation and that, like the sympathetic nervous system, it is modulated by short, medium and long term influences. In both cases there is regulation both at a local and systemic level. Habitual, and recent, lifestyle can exert important cardiovascular effects which must be taken into account in clinical and epidemiological research.

Arterial compliance in obese subjects is improved with dietary plant n-3 fatty acid from flaxseed oil despite increased LDL oxidizability.

The compliance or elasticity of the arterial system, an important index of circulatory function, diminishes with increasing cardiovascular risk. Conversely, systemic arterial compliance improves through eating of fish and fish oil. We therefore tested the value of high intake of alpha-linolenic acid, the plant precursor of fish fatty acids. Fifteen obese people with markers for insulin resistance ate in turn four diets of 4 weeks each; saturated/high fat (SHF), alpha-linolenic acid/low fat (ALF), oleic/low fat (OLF), and SHF. Daily intake of alpha-linolenic acid was 20 g from margarine products based on flax oil. Systemic arterial compliance was calculated from aortic flow velocity and aortic root driving pressure. Plasma lipids, glucose tolerance, and in vitro LDL oxidizability were also measured. Systemic arterial compliance during the first and last SHF periods was 0.42 +/- 0.12 (mean +/- SD) and 0.56 +/- 0.21 units based on milliliters per millimeter of mercury. It rose significantly to 0.78 +/- 0.28 (P < .0001) with ALF; systemic arterial compliance with OLF was 0.62 +/- 0.19, lower than with ALF (P < .05). Mean arterial pressures and results of oral glucose tolerance tests were similar during ALF, OLF, and second SHF; total cholesterol levels were also not significantly different. However, insulin sensitivity and HDL cholesterol diminished and LDL oxidizability increased with ALF. The marked rise in arterial compliance at least with alpha-linolenic acid reflected rapid functional improvement in the systemic arterial circulation despite a rise in LDL oxidizability. Dietary n-3 fatty acids in flax oil thus confer a novel approach to improving arterial function.

Region-specific neuropeptide Y overflows at rest and during sympathetic activation in humans.

Neuropeptide Y coexists with norepinephrine in sympathetic nerves and is coreleased into the circulation on sympathetic activation. Little is known about the regional release of neuropeptide Y in humans under normal conditions or in pathophysiological situations of sympathetic activation or denervation. We measured plasma neuropeptide Y-like immunoreactivity and norepinephrine concentrations in samples taken from the brachial artery; coronary sinus; and internal jugular, antecubital, or hepatic veins in volunteers aged 20 to 64 years. Regional neuropeptide Y overflow at rest was calculated from venoarterial plasma concentration differences and plasma flow, and norepinephrine spillover was determined by [3H]norepinephrine infusion techniques. Cardiac release of neuropeptide Y and norepinephrine was examined in response to various stressors as well as in clinical models of sympathetic activation, cardiac failure, and denervation after cardiac transplantation. In healthy volunteers, cardiac, forearm, and jugular venous sample neuropeptide Y concentrations were similar to arterial levels. Hepatic vein plasma neuropeptide Y was greater than arterial both at rest (119 +/- 5% of arterial, n = 7) and after a meal (132 +/- 12%, n = 7), with neuropeptide Y overflows of 6 +/- 2 and 11 +/- 2 pmol/min, respectively. In contrast, hepatomesenteric norepinephrine spillover was not significantly increased by feeding. Although coronary sinus plasma norepinephrine concentrations increased significantly with the cardiac sympathetic activation accompanying mental arithmetic, coffee drinking, isotonic exercise, and bicycle exercise, only the latter powerful sympathetic stimulus increased neuropeptide Y overflow. Cardiac failure was associated with increased resting release of both norepinephrine and neuropeptide Y from the heart, whereas postcardiac transplant norepinephrine spillover from the heart was reduced. The net overflow of neuropeptide Y to plasma observed at rest across the hepatic circulation, but not the cardiac, forearm, or cerebral circulations, indicates that the gut, the liver, or both make a major contribution to systemic plasma neuropeptide Y levels in humans. Sympathetic activation by exercise produced a modest increase in cardiac neuropeptide Y overflow but to only approximately 25% of the resting input from the gut and without a change in arterial neuropeptide Y concentration. Plasma neuropeptide Y measurements are less sensitive than those of plasma norepinephrine concentrations as an index for quantifying sympathetic neural responses regulating the systemic circulation.

Estrogen enhances basal nitric oxide release in the forearm vasculature in perimenopausal women.

The mechanisms of estrogen-induced cardiovascular protection are incompletely understood. Acute estrogen administration enhances acetylcholine-induced vasorelaxation, suggesting that endothelium-dependent factors may be important. The effect of long-term estrogen supplementation on endothelial function has not been well defined. In this double-blind, randomized study, we examined endothelial function in forearm resistance arteries in 11 perimenopausal women before and after 8 weeks of estrogen supplementation (estradiol valerate, 2 mg daily, n = 6) or placebo (n = 5). Forearm blood flow was measured by venous-occlusion plethysmography, and vasoactive agents were infused through a brachial artery cannula in doses that did not influence blood pressure or heart rate. Estrogen supplementation significantly reduced systolic and diastolic pressures but had no effect on plasma lipoproteins. Estrogen did not alter the vasodilator responses to acetylcholine at doses of 9.25, 18.5, and 37 micrograms/min (rise in forearm blood flow before estrogen: 263 +/- 72%, 288 +/- 66%, and 383 +/- 84%, respectively; after estrogen: 205 +/- 34%, 260 +/- 44%, and 359 +/- 54%, P > .05.). Vasodilator responses to the endothelium-independent agent sodium nitroprusside (1.6 micrograms/min) were also unchanged after estrogen supplementation. However, estrogen enhanced vasoconstrictor responses to the nitric oxide synthase inhibitor NG-mono-methyl-L-arginine at doses of 1, 2, and 4 mumol/min (fall in fore-arm blood flow before estrogen: 13 +/- 9%, 20 +/- 7%, and 26 +/- 8%, respectively; after estrogen: 18 +/- 9%, 36 +/- 7%, and 47 +/- 7%, P = .04). Responses to vasoactive agents were unchanged after administration of placebo. Thus, in perimenopausal women, estrogen supplementation reduces blood pressure and enhances basal but not acetylcholine-induced nitric oxide release in fore-arm resistance arteries.

Effects of in vivo and in vitro L-arginine supplementation on healthy human vessels.

We studied the influence of dietary L-arginine (L-ARG) supplementation on forearm resistance arteries in vivo and the effect of exogenous addition of L-ARG to subcutaneous arteries isolated from gluteal biopsies. Twenty-six healthy males were recruited, and 16 were randomly allocated in a double-blind protocol to receive either oral L-ARG 20 g/day or placebo for 28 days. We examined responses to acetylcholine (ACh), sodium nitroprusside (SNP) and NG-monomethyl-L-arginine (L-NMMA) on forearm resistance arteries using venous occlusion plethysmography performed before and after supplementation of L-ARG (or placebo). L-ARG 20 g/day had no effect on plasma L-ARG levels (% mol based on total amino acid pool; before vs. after L-ARG 3.43 +/- 0.31 vs. 3.76 +/- 0.05), weekly blood pressure (BP) measurements, or plasma biochemical analysis of liver function enzymes, urea, or electrolyte levels. On the other hand, analysis of the major amino acids in plasma showed a significant difference in profile after L-ARG, but not placebo supplementation (Mann Whitney U test, p < 0.05), indicating a domino effect of chronic oral L-ARG supplementation on other amino acids. This may result from a change in appetite and thus protein intake after L-ARG supplementation. At the dose given, neither L-ARG nor placebo had any effect on forearm blood flow (FBF) responses to ACh (area under the dose-response curve, before vs. after L-ARG 1,763 +/- 260.1 vs. 1,862.8 +/- 163.6 U, Student's paired t test; p > 0.05), SNP, or L-NMMA. Gluteal skin biopsies were performed on 10 different untreated subjects. Subcutaneous arteries were isolated and mounted as ring preparations in isometric small vessel myographs. Full concentration-response curves to norepinephrine (NE), ACh, substance P, and a single response to SNP (10 microM) were obtained with and without addition of either L- or D-ARG 10 microM. Both L-ARG [-log EC50 (M) before vs. after arginine 7.12 +/- 0.15 vs. 6.66 +/- 0.16, Student's paired t test, p < 0.005] and D-ARG [-log EC50 (M) before vs. after arginine 7.36 +/- 0.17 vs. 6.85 +/- 0.18; Student's paired t test, p < 0.05] significantly antagonized responses to NE in subcutaneous arteries isolated from healthy humans. With the exception of a subset of vessels in which some endothelial dysfunction was observed, neither of the isomers of arginine had any effect on the responses to ACh, substance P, or SNP. In the subset vessels already described (n = 5), in which responses to ACh were < 90% maximal dilatation, L- but not D-ARG significantly increased the potency to ACh [-log EC50 (M) before vs. after L-ARG 7.42 +/- 0.20 vs. 8.27 +/- 0.28. Student's paired t test, p < 0.05]. We conclude that oral supplementation with L-ARG 20 g/day for 28 days does not affect endothelial function in normal healthy adults, possibly because the dose given in the current study was inadequate or because chronic oral administration leads to dissipation of arginine to other pathways, as evidenced by the change in total amino acid profile but not L-ARG plasma concentration, or because L-ARG cannot improve normal endothelium-mediated vasodilatation. These concepts are supported by our findings that responses to ACh and substance P were not altered by L-ARG in subcutaneous arteries isolated from healthy subjects.

Dietary supplementation with L-arginine fails to restore endothelial function in forearm resistance arteries of patients with severe heart failure.

OBJECTIVES: We sought to examine the efficacy of dietary supplementation of L-arginine on endothelium-dependent vasodilation in patients with congestive heart failure. BACKGROUND: Endothelial dysfunction, as evidenced by a diminished response to such vasodilators as acetylcholine, is well defined in patients with heart failure. These responses are improved by intraarterial infusion with L-arginine. Because L-arginine is a semi-essential amino acid, we investigated the effects of dietary L-arginine on endothelium-dependent vasodilation in these patients. METHODS: Twenty patients with heart failure (New York Heart Association functional class III/IV, mean [+/- SE] age 51.3 +/- 1.7 years) and seven healthy control subjects (mean age 52.6 +/- 3.3 years) were studied. All patients continued taking their usual treatment. Responses to acetylcholine and sodium nitroprusside were determined using forearm plethysmography. Patients with heart failure received either L-arginine (20 g/day every day for 28 days) or placebo (vehicle syrup in equal amounts) in a double-blind protocol. The calculated power of the study was between 62% and 80% to detect a 30% to 40% change in area under the dose-response (forearm vascular resistance) curve. RESULTS: Responses to acetylcholine, but not to sodium nitroprusside, were significantly attenuated in patients with heart failure compared with control subjects (mean area under curve [AUC], control subjects vs. patients with heart failure: 1,125.4 +/- 164.5 vs. 617.3 +/- 116.6 U, p < 0.05, by Student t test). A significant increase in urea and aspartate transaminase levels in patients receiving active L-arginine treatment was observed. Responses to acetylcholine (AUC; before vs. after L-arginine: 641.5 +/- 126.7 vs. 695.9 +/- 151.9 U) and sodium nitroprusside were not affected by either L-arginine or placebo. CONCLUSIONS: Endothelial dysfunction was apparent in patients with heart failure despite rigorous vasoactive treatment. Oral administration with L-arginine was ineffective in influencing endothelial function in these patients.

Effects of dietary marine oil supplementation on reactivity of human buttock subcutaneous arteries and forearm veins in vitro.

1. The vascular reactivity of resistance arteries isolated from gluteal skin biopsies and veins isolated from forearms of subjects fed marine oils were examined. 2. Twenty seven healthy adult males were randomly allocated to one of two different treatment groups. The first group received maxEPA (eicosapentaenoic acid 0.178 g g-1; docosahexaenoic acid 0.116 g g-1) capsules 10 g per day for 28 days while the second group received an equivalent amount of mixed oil placebo capsules. Biopsies were performed on day 29 (13 for gluteal sections; 14 for forearm vein biopsies). Subcutaneous arteries and veins were mounted in myographs and standard organ baths, respectively. 3. The internal diameter of the subcutaneous arteries at a calculated transmural pressure of 100 mmHg averaged 183.7 +/- 10.3 microns in the maxEPA group and 182.6 +/- 19.8 microns in the placebo controls. Arteries from subjects on maxEPA demonstrated increased sensitivity to angiotensin II (maxEPA vs placebo: -log EC50 (M) -8.36 +/- 0.18 vs -7.91 +/- 0.14) but not to noradrenaline or 5-hydroxytryptamine. Concentration-response curves to acetylcholine, substance P and sodium nitroprusside obtained for noradrenaline precontracted vessels were unaltered with marine oil treatment as was the concentration-response curve to calcium in K(+)-depolarized vessels. 4. Vein internal diameter at a calculated transmural pressure of 20 mmHg averaged 3.06 +/- 0.23 mm in the maxEPA group and 2.96 +/- 0.89 in the placebo group. Responses to noradrenaline, 5-hydroxytryptamine, angiotensin II and endothelin-1 were obtained in the absence and presence of indomethacin (1 microM) in veins from both maxEPA and placebo-treated subjects. Neither dietary supplementation with marine oils nor indomethacin had any effect on the responses obtained to these agonists.5. The major finding of the present study was that in general, maxEPA supplementation did not affect responses to various vasoactive substances on isolated subcutaneous arteries or forearm veins. An exception was the observation of an enhanced response to angiotensin II in subcutaneous resistance arteries studied in vitro. This effect was selective for angiotensin II and was not apparent in veins isolated from the forearm.

Cardiovascular-risk reduction: initial diuretic therapy compared with calcium-antagonist (felodipine) therapy for primary hypertension.

Drug therapy for hypertension has failed to demonstrate a significant reduction in coronary mortality. We compared a calcium-antagonist agent, felodipine, with diuretic therapy as a first-line antihypertensive treatment in a randomized study, to assess the effects of six months of each regimen on over-all cardiovascular risk. Both regimens lowered blood pressure to less than 85 mmHg by one month. Felodipine alone was sufficient to control blood pressure in 90% of patients, while 50% of patients who were receiving diuretic therapy required a second agent for control. Diuretic therapy produced a 10% fall in serum potassium levels (P less than 0.001) and a three-fold increase in plasma renin activity (P less than 0.005) by one month; and a 6% rise in serum cholesterol levels (P less than 0.05) and a 38% rise in serum triglyceride levels (P less than 0.05) by three months. Felodipine did not influence these measurements, but caused a 43% increase in plasma noradrenaline levels by one month of therapy (P less than 0.025). In both groups, a significant fall occurred in the risk percentile score at six months, as calculated from the Multiple Risk Factor Intervention Trial data. However, the decrease was significantly greater in the felodipine group at six months (45% compared with 29%; P less than 0.05). Thus, when doses were titrated to achieve equivalent effects on blood pressure, felodipine had the advantages over diuretic treatment of being effective as monotherapy, of having fewer metabolic effects, and of reducing cardiovascular risk to a greater degree.