Randomized trial of nutrition education added to internet-based information and exercise at the work place for weight loss in a racially diverse population of overweight women.

OBJECTIVE: Obesity in the United States is highly prevalent, approaching 60% for black women. We investigated whether nutrition education sessions at the work place added to internet-based wellness information and exercise resources would facilitate weight and fat mass loss in a racially diverse population of overweight female employees. METHODS: A total of 199 (average body mass index 33.9±6.3 kg m(-2)) nondiabetic women (57% black) at our institution were randomized to a 6-month program of either internet-based wellness information (WI) combined with dietitian-led nutrition education group sessions (GS) weekly for 3 months and then monthly with shift in emphasis to weight loss maintenance (n=99) or to WI alone (n=100). All were given access to exercise rooms convenient to their work site. Fat mass was measured by dual-energy X-ray absorptiometry. RESULTS: WI+GS subjects lost more weight than WI subjects at 3 months (-2.2±2.8 vs -1.0±3.0 kg, P>0.001). Weight (-2.7±3.9 vs -2.0±3.9 kg) and fat mass (-2.2±3.1 vs -1.7±3.7 kg) loss at 6 months was significant for WI+GS and WI groups (both P<0.001), but without significant difference between groups (both P>0.10); 27% of the WI+GS group achieved 5% loss of initial weight as did 18% of the WI group (P=0.180). Blacks and whites similarly completed the study (67 vs 74%, P=0.303), lost weight (-1.8±3.4 vs -3.3±5.2 kg, P=0.255) and fat mass (-1.6±2.7 vs -2.5±4.3 kg, P=0.532), and achieved 5% loss of initial weight (21 vs 32%, P=0.189), irrespective of group assignment. CONCLUSION: Overweight women provided with internet-based wellness information and exercise resources at the work site lost weight and fat mass, with similar achievement by black and white women. Additional weight loss benefit of nutrition education sessions, apparent at 3 months, was lost by 6 months and may require special emphasis on subjects who fail to achieve weight loss goals to show continued value.

Insulin and extremity muscle mass in overweight and obese women.

BACKGROUND: Obesity disproportionately affects women, especially those of African descent, and is associated with increases in both fat and muscle masses. OBJECTIVE: Although increased extremity muscle mass may be compensatory to fat mass load, we propose that elevated insulin levels resulting from diminished insulin sensitivity may additionally contribute to extremity muscle mass in overweight or obese women. METHODS: The following measurements were performed in 197 non-diabetic women (57% black, 35% white; age 46±11 years (mean±s.d.), body mass index (BMI) range 25.0-57.7 kg m(-2)): dual-energy X-ray absorptiometry for fat and extremity muscle masses; exercise performance by duration and peak oxygen consumption (VO2 peak) during graded treadmill exercise; fasting insulin and, in 183 subjects, insulin sensitivity index (SI) calculated from the minimal model. RESULTS: SI (range 0.5-14.1 l mU(-1 )min(-1)) was negatively, and fasting insulin (range 1.9-35.6 µU ml(-1)) positively associated with extremity muscle mass (both P<0.001), independent of age and height. Sixty-seven percent of women completed 6 months of participation in a weight loss and exercise program: we found a significant association between reduction in fasting insulin and a decrease in extremity muscle mass (P=0.038), independent of reduction in fat mass or improvement in exercise performance by VO2 peak and exercise duration, and without association with change in SI or interaction by race. CONCLUSIONS: Hyperinsulinemia in overweight or obese women is associated with increased extremity muscle mass, which is partially reversible with reduction in fasting insulin concentration, consistent with the stimulatory effects of insulin on skeletal muscle.

Cardiovascular potential of BM-derived stem and progenitor cells.

Observational and experimental studies suggest that BM-derived stem and progenitor cells may have the capacity to repair damaged cardiovascular tissue and initiate blood vessel growth in regions of ischemia. Despite controversies regarding transdifferentiation potential of adult stem cells, clinical trials are underway testing the hypothesis that BM cell-based approaches to a broad spectrum of cardiovascular diseases and disease presentations will be safe and effective strategies for patient management.

Arterial wall MRI characteristics are associated with elevated serum markers of inflammation in humans.

Inflammation contributes to atherosclerosis, but assessment in humans is largely restricted to measurement of markers in blood. We determined whether MRI properties of large arteries were associated with markers of inflammation in serum. Double inversion recovery, fast spin-echo images of the common carotid arteries and infrarenal aorta were obtained at 1.5 T both before and after gadolinium-DTPA (0.1 mmol/kg) in 52 subjects > or =40 years of age, 17 of whom had no risk factors for atherosclerosis and thus served as controls. Twenty-two study participants had increases in wall thickness (14), T2-weighted signal intensity (11), and/or contrast enhancement values (7) that were >2 standard deviations (SDs) from control group mean values. Ten subjects in this group had evidence of focal plaques in the carotids (5) and/or aorta (6). Compared with the remaining 30 subjects, these 22 had significantly higher levels of interleukin-6 (3.53 +/- 2.46 vs. 1.97 +/- 1.37 pg/mL, P = 0.004), C-reactive protein (0.56 +/- 0.98 vs. 0.30 +/- 0.52 mg/dL, P = 0.019), vascular cell adhesion molecule-1 (572 +/- 153 vs. 471 +/- 130 ng/mL, P = 0.012), and intercellular adhesion molecule-1 (244 +/- 80 vs. 202 +/- 45 ng/mL, P = 0.015), and nonsignificant differences in levels of E-selectin (46.1 +/- 18.9 vs. 42.3 +/- 11.3 ng/mL, P = 0.369). Thus, MRI characteristics of the aorta and carotid arteries were associated with elevated serum markers of inflammation, frequently in the absence of definite atheroma. MRI of large arteries may provide a new approach to investigate the contribution of inflammation to atherogenesis.

Noninvasive determination of spatially resolved and time-resolved tissue perfusion in humans during nitric oxide inhibition and inhalation by use of a visible-reflectance hyperspectral imaging technique.

BACKGROUND: Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO(2)) as an index of skin tissue perfusion. METHODS AND RESULTS: To simulate vascular endothelial dysfunction, N(G)-monomethyl-L-arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO(2) perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7+/-4.9% and percentage of HbO(2) by 6.5+/-0.1 (P=0.002 and P<0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9+/-7.3%, and the percentage of HbO(2) decreased by 3.6+/-0.1 (P=0.007 and P<0.001, respectively, versus room air L-NMMA responses). CONCLUSIONS: Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO(2) in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) restoration of HbO(2) toward basal values with improved blood flow during inhalation of NO. This imaging method may provide an effective approach for time-resolved noninvasive monitoring of skin hemoglobin oxygen saturation and assessment of responses to therapeutic interventions in patients with vascular disease.

Raloxifene-mediated increase in matrix metalloproteinase-1 production by activated monocytes.

Matrix metalloproteinases (MMPs), proteolytic enzymes produced by monocytes, may contribute to atherosclerotic arterial wall remodeling and to plaque rupture. Because estrogen influences the synthesis of MMPs, we examined the effect of raloxifene, a selective estrogen receptor modulator, on monocyte MMP production. Human primary blood monocytes treated with raloxifene (10 micromol/L) in the presence of lipopolysaccharide (LPS) or tumor necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor induced a 2- to 3-fold increase in MMP-1 production by monocytes. The enhancement of MMP-1 production by raloxifene in LPS-activated monocytes occurred through a cyclooxygenase-2- and prostaglandin E(2)-independent mechanism. Additionally, compared with monocytes acquired during the placebo phase, peripheral blood monocytes from 5 of 6 healthy postmenopausal women treated with raloxifene (60 mg daily for 1 month) in a clinical trial produced significantly higher levels of MMP-1 when the monocytes were activated with LPS. Furthermore, serum obtained during the raloxifene phase from 4 of these subjects, when added to control monocytes, significantly enhanced LPS-induced MMP-1 production compared with that from serum obtained during the placebo phase. In summary, raloxifene increases the production of MMP-1 in activated monocytes; this effect may be favorable in atherosclerotic arterial wall remodeling but unfavorable for plaque stability.

Effects of inhaled nitric oxide on regional blood flow are consistent with intravascular nitric oxide delivery.

Nitric oxide (NO) may be stabilized by binding to hemoglobin, by nitrosating thiol-containing plasma molecules, or by conversion to nitrite, all reactions potentially preserving its bioactivity in blood. Here we examined the contribution of blood-transported NO to regional vascular tone in humans before and during NO inhalation. While breathing room air and then room air with NO at 80 parts per million, forearm blood flow was measured in 16 subjects at rest and after blockade of forearm NO synthesis with N(G)-monomethyl-L-arginine (L-NMMA) followed by forearm exercise stress. L-NMMA reduced blood flow by 25% and increased resistance by 50%, an effect that was blocked by NO inhalation. With NO inhalation, resistance was significantly lower during L-NMMA infusion, both at rest and during repetitive hand-grip exercise. S-nitrosohemoglobin and plasma S-nitrosothiols did not change with NO inhalation. Arterial nitrite levels increased by 11% and arterial nitrosyl(heme)hemoglobin levels increased tenfold to the micromolar range, and both measures were consistently higher in the arterial than in venous blood. S-nitrosohemoglobin levels were in the nanomolar range, with no significant artery-to-vein gradients. These results indicate that inhaled NO during blockade of regional NO synthesis can supply intravascular NO to maintain normal vascular function. This effect may have application for the treatment of diseases characterized by endothelial dysfunction.

Daily catheter-directed single dosing of t-PA in treatment of acute deep venous thrombosis of the lower extremity.

The strong fibrin affinity of recombinant tissue plasminogen activator (rt-PA) theoretically obviates continuous infusion or replacement of t-PA after direct intrathrombic injection. This hypothesis led the authors to evaluate single daily catheter-directed injection of rt-PA as a thrombolytic treatment for acute deep vein thrombosis of the lower extremity. Once-daily injection of rt-PA was performed in large thrombosed veins (popliteal or larger) with use of pulse-spray catheters and in small thrombosed veins in patients' calves with use of 3-4-F coaxial catheters. Patients received only full systemic anticoagulation on his/her patient care unit. This dosing regimen has been tested in 10 patients (12 legs) with a maximum dose of 50 mg per leg per day. Extensive thrombolysis was achieved in nine patients and partial thrombolysis was achieved in one patient, at an average total dose of 106 mg of rt-PA per leg. Minor bleeding was seen in three patients and no transfusions were needed. Our technique and the rationale for this pilot study is the focus of this article.

Selective estrogen receptor modulator effects on serum lipoproteins and vascular function in postmenopausal women and in hypercholesterolemic men.

Epidemiological observations, clinical mechanistic studies, and basic laboratory research suggest that estrogen therapy is associated with beneficial cardiovascular effects in postmenopausal women. Estrogen has a multitude of biological effects that may account for this apparent benefit (which remains to be proved in randomized clinical trials), including favorable effects on the lipid profile, increased endothelial nitric oxide bioactivity, and enhanced fibrinolysis. However, long-term estrogen therapy increases the risk of breast and endometrial cancers. Raloxifene, a benzothiophene derivative that binds to the estrogen receptor, is a selective estrogen receptor modulator, producing estrogen-agonist effects in some tissues (liver, bone) and estrogen-antagonistic effects in others (breast, uterus), and may prove to be an option for women with atherosclerosis or its risk factors. This review updates the current knowledge of the biological effects of selective estrogen receptor modulators of potential cardiovascular importance in postmenopausal women.

Antioxidant effect of estrogen on cytomegalovirus-induced gene expression in coronary artery smooth muscle cells.

BACKGROUND: Pathogens infecting the arterial wall with resultant inflammation may contribute to atherogenesis. Human coronary artery smooth muscle cells (SMCs) infected with human cytomegalovirus (CMV) demonstrate a rapid increase in reactive oxygen species (ROSs), with activation of genes involved in viral replication and inflammation. Because estrogen appears to have antioxidant properties, we wished to determine whether this hormone attenuates SMC responses to CMV infection. METHODS AND RESULTS: Using confocal microscopy and an intracellular fluorescent dye activated by ROSs, we found that 17beta-estradiol (0.1 to 10 nmol/L) and its stereoisomer 17alpha-estradiol (which has low affinity for the estrogen receptor) dose-dependently inhibited ROS generation in CMV-infected SMCs. These effects were not blocked by the estrogen receptor inhibitor ICI 182,780. 3-Methoxyestrone, which lacks the phenolic hydroxyl group, did not interfere with ROS generation. We found that 17beta-estradiol and 17alpha-estradiol, but not 3-methoxyestrone, prevented binding of nuclear factor (NF)-kappaB to DNA. Furthermore, in SMCs transfected with the reporter constructs 3XkappaB-CAT, MIEP-CAT, or ICAM-CAT, cotransfection with a CMV-IE72 expression plasmid caused promoter and CAT activation. Treatment with 17beta-estradiol and 17alpha-estradiol, but not 3-methoxyestrone, inhibited CAT activity and, in CMV-infected SMCs, prevented IE72 and ICAM-1 protein expression and cytopathic effects. CONCLUSIONS: These findings indicate that estrogen molecules with an A-ring hydroxyl group have estrogen receptor-independent anti-CMV effects at physiological concentrations by inhibiting ROS generation, NF-kappaB activation, NF-kappaB-dependent transcription, and viral replication. To the extent that chronic infection of the vascular wall with CMV contributes to atherogenesis, these antioxidant actions of estrogen may be of therapeutic importance.

Increased activity of endogenous endothelin in patients with hypercholesterolemia.

OBJECTIVE: We sought to assess the activity of endogenous endothelin-1 (ET-1) in hypercholesterolemic patients using antagonists of ET-1 receptors. BACKGROUND: Endothelial dysfunction in hypercholesterolemic patients may contribute to their risk of premature atherosclerosis. Endothelin, a peptide released by endothelial cells, may be involved in this process by activating smooth muscle cell mitogenesis and leukocyte adhesion. METHODS: Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intra-arterial infusion of a selective blocker of ETA receptors (BQ-123) and, on a separate occasion, to ET-1 were measured in 12 hypercholesterolemic patients and 12 normal control subjects. In addition, on a different day, six hypercholesterolemic patients received co-infusion of BQ- 123 and BQ-788 (a selective blocker of ETB receptors). RESULTS: In normal subjects, BQ-123 did not significantly modify FBF from baseline (p = 0.78); however, in hypercholesterolemic patients, BQ-123 administration resulted in a significant vasodilator response (p < 0.001). Administration of exogenous ET-1 resulted in similar vasoconstrictor responses in patients (37%) and control subjects (35%) (p = 0.83). In hypercholesterolemic patients, the vasodilator response to selective ETA blockade was reversed by nonselective blockade of ET-1 receptors obtained by co-infusion of BQ-123 and BQ-788. CONCLUSIONS: The vascular activity of endogenous ET-1 is enhanced in hypercholesterolemic patients, whereas their sensitivity to exogenous ET-1 is unchanged. These findings suggest increased production of ET-1, which may participate in the pathophysiology of vascular disease characteristic of hypercholesterolemia.

Divergent effects of hormone therapy on serum markers of inflammation in postmenopausal women with coronary artery disease on appropriate medical management.

OBJECTIVES: The goal of our study was to determine whether hormone therapy alters markers of inflammation in postmenopausal women with chronic stable coronary artery disease (CAD) on appropriate medical management. BACKGROUND: Hormone therapy reduces some markers of inflammation associated with atherosclerosis risk (cell adhesion molecules) but increases levels of another marker of inflammation--C-reactive protein-in healthy postmenopausal women. METHODS: Ten women (average age 66 years; range 59 to 76 years) with CAD on medical management (including aspirin [9], statin lipid-lowering therapy [7], angiotensin-converting enzyme inhibitors [3]) were randomly assigned to conjugated equine estrogens 0.625 mg (combined with medroxyprogesterone acetate 2.5 mg daily in five women with uterus intact) or placebo(s) daily for one month with crossover to the alternate therapy after one month off of hormone treatment in a double-blind study. At the end of each treatment phase, the following markers of inflammation were measured in serum: interleukin-6, C-reactive protein, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and matrix metalloproteinase-9. RESULTS: Hormone therapy significantly lowered serum levels of cell adhesion molecules E-selectin (46.9+/-18.3 vs. 56.3+/-20.6 ng/mL, p = 0.006), intercellular adhesion molecule-1 (282+/-74 vs. 304+/-78 ng/mL, p = 0.013) and vascular cell adhesion molecule-1 (605+/-218 vs. 657+/-214 ng/mL, p = 0.01) but increased levels of matrix metalloproteinase-9 (648+/-349 vs. 501+/-285 ng/mL, p = 0.02). Interleukin-6 (4.33+/-4.78 vs. 3.04+/-1.47 pg/mL, p = 0.283) and C-reactive protein (0.88+/-1.13 vs. 0.61+/-0.50 mg/dL, p = 0.358) were not significantly elevated on hormone therapy compared with placebo values. CONCLUSIONS: Hormone therapy has divergent effects on serum markers of inflammation in women with CAD. Reduction in levels of cell adhesion molecules may reduce attachment of white blood cells to the vessel wall, but increases in matrix metalloproteinase-9 within the vessel wall could digest and weaken fibrous caps of vulnerable plaques, thus provoking thrombosis.

Competition for p300 regulates transcription by estrogen receptors and nuclear factor-kappaB in human coronary smooth muscle cells.

Previous studies suggest that estrogen may prevent expression of cell adhesion molecules implicated in vascular inflammation associated with atherosclerosis. We demonstrate the interaction and reciprocal interference of estrogen receptors (ERs) with p65, the nuclear factor-kappaB component, in smooth muscle cells that express ERalpha and ERss after exposure to 17ss-estradiol for 48 to 72 hours. ER and p65 do not associate directly, as shown by lack of coprecipitation, but instead compete for limiting amounts of p300, a close relative of the CREB-binding protein. Overexpressed p300 significantly reduced the inhibitory effect of ER on p65-dependent transcription as well as the inhibitory effect of p65 on ER-dependent transcription. These actions were ligand-dependent. The expression of both ER and nuclear factor-kappaB-dependent reporter genes was partially rescued from ER/p65 mutual inhibition by transient transfection of smooth muscle cells with a p300 expression vector. These actions of 17ss-estradiol may play an important role in the cytokine-induced expression of immune and inflammatory genes implicated in atherogenesis.

Role of circulating nitrite and S-nitrosohemoglobin in the regulation of regional blood flow in humans.

To determine the relative contributions of endothelial-derived nitric oxide (NO) vs. intravascular nitrogen oxide species in the regulation of human blood flow, we simultaneously measured forearm blood flow and arterial and venous levels of plasma nitrite, LMW-SNOs and HMW-SNOs, and red cell S-nitrosohemoglobin (SNO-Hb). Measurements were made at rest and during regional inhibition of NO synthesis, followed by forearm exercise. Surprisingly, we found significant circulating arterial-venous plasma nitrite gradients, providing a novel delivery source for intravascular NO. Further supporting the notion that circulating nitrite is bioactive, the consumption of nitrite increased significantly with exercise during the inhibition of regional endothelial synthesis of NO. The role of circulating S-nitrosothiols and SNO-Hb in the regulation of basal vascular tone is less certain. We found that low-molecular-weight S-nitrosothiols were undetectable and S-nitroso-albumin levels were two logs lower than previously reported. In fact, S-nitroso-albumin primarily formed in the venous circulation, even during NO synthase inhibition. Whereas SNO-Hb was measurable in the human circulation (brachial artery levels of 170 nM in whole blood), arterial-venous gradients were not significant, and delivery of NO from SNO-Hb was minimal. In conclusion, we present data that suggest (i) circulating nitrite is bioactive and provides a delivery gradient of intravascular NO, (ii) S-nitroso-albumin does not deliver NO from the lungs to the tissue but forms in the peripheral circulation, and (iii) SNO-Hb and S-nitrosothiols play a minimal role in the regulation of basal vascular tone, even during exercise stress.

Cardiac sympathetic denervation in Parkinson disease.

BACKGROUND: In Parkinson disease, orthostatic hypotension can result from L-dopa treatment or from sympathetic neurocirculatory failure. The latter is detected by abnormal blood pressure responses to the Valsalva maneuver and can be associated with loss of functional cardiac sympathetic nerve terminals. OBJECTIVE: To determine the frequency of cardiac sympathetic denervation in Parkinson disease, with or without sympathetic neurocirculatory failure, and its association with disease duration, severity, and L-dopa treatment DESIGN: Intergroup comparisons in resting patients. SETTING: National Institutes of Health Clinical Center, Bethesda, Maryland. PATIENTS: 29 patients with Parkinson disease (9 with sympathetic neurocirculatory failure, 10 who had stopped receiving or had never been treated with L-dopa), 24 patients with multiple-system atrophy (17 with sympathetic neurocirculatory failure, 8 receiving L-dopa), 7 patients with pure autonomic failure, 33 controls with episodic or persistent orthostatic intolerance without sympathetic neurocirculatory failure, and 19 normal volunteers. MEASUREMENTS: Beat-to-beat blood pressure responses to the Valsalva maneuver, interventricular septal 6-[18F]fluorodopamine-derived radioactivity, cardiac extraction fraction of [3H]norepinephrine, appearance rate of norepinephrine in coronary sinus plasma (cardiac norepinephrine spillover) and venous-arterial differences in levels of dihydroxyphenylglycol (DHPG) and endogenous L-dopa. RESULTS: Of the 29 patients with Parkinson disease, 9 with sympathetic neurocirculatory failure and 11 without had low septal 6-[18F]fluorodopamine-derived radioactivity (2861 +/- 453 Bq/mL per MBq/kg and 5217 +/- 525 Bq/mL per MBq/kg, respectively). All 6 patients with Parkinson disease and decreased 6-[18F]fluorodopamine-derived radioactivity who underwent right-heart catheterization had a decreased cardiac extraction fraction of [3H]norepinephrine and virtually no cardiac norepinephrine spillover or venous-arterial increments in plasma levels of DHPG and L-dopa. Sympathetic neurocirculatory failure and decreased 6-[18F]fluorodopamine-derived radioactivity were unrelated to disease duration, disease severity, or L-dopa treatment CONCLUSIONS: Many patients with Parkinson disease-including all those with sympathetic neurocirculatory failure-have evidence of cardiac sympathetic denervation. This suggests that loss of catecholamine innervation in Parkinson disease occurs in the nigrostriatal system in the brain and in the sympathetic nervous system in the heart

Interactions between nitric oxide and endothelin in the regulation of vascular tone of human resistance vessels in vivo.

Endothelial release of nitric oxide (NO) contributes to the regulation of vascular tone by inducing vascular relaxation. In addition, NO may inhibit the synthesis and hemodynamic effects of endothelin-1 (ET-1), a powerful endothelium-derived vasoconstrictor peptide that may stimulate NO production. However, whether NO and ET-1 physiologically interact to regulate vascular tone in humans has not been defined. In this study, the interactions between the L-arginine NO pathway and the ET-1 system in the regulation of vascular tone in human forearm resistance vessels were examined in vivo. Vasomotor response to the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 4 micromol/min for 30 minutes) was measured during either saline infusion or blockade of ET-1 receptors. Endothelin-A (ET(A)) and endothelin-B (ET(B)) receptor blockade was achieved by infusion of BQ-123 (100 nmol/min) and BQ-788 (50 nmol/min), respectively, separately and in combination. Drugs were infused into the brachial artery, and the forearm blood flow (FBF) response was measured by strain-gauge plethysmography. During saline infusion, L-NMMA administration significantly decreased FBF (25%, P<0.01 versus baseline). This effect was significantly blunted during nonselective blockade of ET-1 receptors (7% decrease in FBF, P=0.02 versus the effect of L-NMMA during saline infusion). Selective ET(A) blockade did not modify the vasoconstrictor response to L-NMMA (26% decrease in FBF, P=0.66 versus the effect of L-NMMA during saline infusion), but selective ET(B) receptor antagonism caused significant diminution of the hemodynamic response to NO inhibition (8% decrease in FBF, P=0.04 versus the effect of L-NMMA during saline infusion). Thus ET-1 contributes to the regulation of vascular tone by stimulating NO activity. This effect is mediated through endothelial ET(B) receptors and may be relevant in conditions associated with endothelial dysfunction.