Aerobic Exercise Training Combined with Local Strength Exercise Restores Muscle Blood Flow and Maximal Aerobic Capacity in Long-Term Hodgkin Lymphoma Survivors

BACKGROUND

It is unclear whether muscle blood flow (MBF) is altered in long-term Hodgkin Lymphoma (HL) survivors. We test the hypothesis that: 1) MBF response during mental stress (MS) is impaired in long-term HL survivors; 2) Aerobic exercise training combined with local strength exercise (ET) restores MBF responses during MS in these survivors.

METHODS

Eighteen 5-year HL survivors and 10 aged-paired healthy subjects (HC) were studied. Twenty HL survivors were randomly divided into two groups: Exercise-trained (HLT, n=10) and untrained (HLUT, n=10). Maximal aerobic capacity was evaluated by a cardiopulmonary exercise test and forearm blood flow (FBF) by venous occlusion plethysmography. MS was elicited by Stroop Color Word Test. ET was conducted for four months, three/week for 60 minutes each session. The aerobic exercise intensity corresponded to anaerobic threshold up to 10% below the respiratory compensation point. The strength exercises consisted of 2-3 sets of chest press, pulley and squat exercises, 12-15 repetitions each exercise at 30-50% of the maximal voluntary contraction.

RESULTS

Baseline was similar in HL survivors and HC, except peak oxygen consumption (peak VO2, p=0.013) and FBF (p=0.006) that were lower in the HL survivors. FBF responses during MS were lower in HL survivors (p<0.001). ET increased peak VO2 (11.59±3.07%, p=0.002), and FBF at rest (33.74±5.13%, p<0.001) and during MS (24±5.31%, p=0.001). Further analysis showed correlation between the changes in peak VO2 and the changes in FBF during MS (r=0.711, p=0.001).

CONCLUSION

Long-term HL survivors have impaired MBF responses during MS. ET restores MBF responses during MS.

The Effect of Additional Treatment with Empagliflozin or Semaglutide on Endothelial Function and Arterial Stiffness in Subjects with Type 1 Diabetes Mellitus-ENDIS Study

We investigated the effect of additional treatment with newer antidiabetic drugs on endothelium function and arterial stiffness in subjects with type 1 diabetes mellitus (T1DM) without cardiovascular diseases. A total of 89 participants, all users of CGMS (continuous monitoring glucose system), were randomized into three comparable groups, receiving empagliflozin (E; n = 30), receiving semaglutide (S; n = 30), and a control group (C; n = 29). At baseline and 12 weeks post treatment, we measured FMD (brachial artery flow-mediated dilation) and FBF (forearm blood flow as reactive hyperemia assessed with strain gauge plethysmography) as parameters of endothelial function, as well as pulse wave velocity (PWV) and peripheral resistance as parameters of arterial stiffness. Improvement in FMD was significant in both intervention groups compared to controls (E group 2.0-fold, p = 0.000 and S group 1.9-fold, p = 0.000), with no changes between those two groups (p = 0.745). During the evaluation of FBF, there were statistically insignificant improvements in both therapeutic groups compared to controls (E group 1.39-fold, p = 0.074 and S group 1.22-fold, p = 0.701). In arterial stiffness parameters, improvements were seen only in the semaglutide group, with a decline in peripheral resistance by 5.1% (p = 0.046). We can conclude that, for arterial stiffness, semaglutide seems better, but both drugs positively impact endothelial function and, thus, could also have a protective role in T1DM.

Sugar-sweetened beverage consumption and vascular function in Hispanic and non-Hispanic males

Introduction: Hispanic men have one of the highest consumptions of sugar-sweetened beverages in the United States. Frequent sugar-sweetened beverage consumption has been associated with higher incidence of cardiovascular disease through altered vascular function. Cardiovascular disease is the second leading cause of death in the Hispanic population. The purpose of this study is to assess the difference in vascular function between Hispanic men and non-Hispanic men and whether this difference is attributed to ethnic predisposition (i.e. ethnicity) or other risk factors, such as sugar-sweetened beverage consumption. Method: Reactive hyperemia forearm blood flow of 11 Hispanic males and 11 non-Hispanic males was measured via venous occlusion plethysmography. Interview-administered questionnaires gathered anthropometric, medical, dietary, and physical activity data for participants. Results: No significant differences were found in peak or total reactive hyperemia forearm blood flow between matched pairs (p = 0.924). Significant differences were also not observed in dietary factors, sugar-sweetened beverage consumption (p = 0.693), or physical activity (0.720). Conclusion: No statistical differences in body composition, dietary intake, physical activity, and vascular function were observed between Hispanic and non-Hispanic males. Environmental and lifestyle factors may play a larger role than ethnicity in the development of cardiovascular disease. Recruitment based on ethnicity alone yielded a population that was similar regarding SSB consumption and vascular function.

Sex differences in the vascular response to sympathetic activation during acute hypoxaemia

NEW FINDINGS

What is the central question of this study? Sympathetically mediated vasoconstriction is preserved during hypoxaemia in humans, but our understanding of vascular control comes from predominantly male cohorts. We tested the hypothesis that young women attenuate sympathetically mediated vasoconstriction during steady-state hypoxaemia, whereas men do not? What is the main finding and its importance? Sympathetically mediated vasoconstriction is preserved or even enhanced during steady-state hypoxia in young men, and the peripheral vascular response to sympathetic activation during hypoxaemia is attenuated in young women. These data advance our understanding of sex-related differences in hypoxic vascular control.

ABSTRACT

Activation of the sympathetic nervous system causes vasoconstriction and a reduction in peripheral blood flow. Sympathetically mediated vasoconstriction may be attenuated during systemic hypoxia to maintain oxygen delivery; however, in predominantly male participants sympathetically mediated vasoconstriction is preserved or even enhanced during hypoxaemia. Given the potential for sex-specific differences in hypoxic vascular control, prior results are limited in application. We tested the hypothesis that young women attenuate sympathetically mediated vasoconstriction during steady-state hypoxaemia, whereas men do not. Healthy young men (n = 13, 25 ± 4 years) and women (n = 11, 24 ± 4 years) completed two trials consisting of a 2-min cold pressor test (CPT, a well-established sympathoexcitatory stimulus) during baseline normoxia and steady-state hypoxaemia. Beat-to-beat blood pressure (finger photoplethysmography) and forearm blood flow (venous occlusion plethysmography) were measured continuously. Total and forearm vascular conductance (TVC and FVC, respectfully) were calculated. A change (Δ) in TVC and FVC from steady-state during the last 1 min of CPT was calculated and differences between normoxia and systemic hypoxia were assessed. In men, the reduction in TVC during CPT was greater during hypoxia compared to normoxia (ΔTVC, P = 0.02), whereas ΔTVC did not differ between conditions in women (P = 0.49). In men, ΔFVC did not differ between normoxia and hypoxia (P = 0.92). In women, the reduction in FVC during CPT was attenuated during hypoxia (ΔFVC, P < 0.01). We confirm sympathetically mediated vasoconstriction is preserved or enhanced during hypoxaemia in young men, whereas peripheral vascular responsiveness to sympathetic activation during hypoxaemia is attenuated in young women. The results advance our understanding of sex-related differences in hypoxic vascular control.

Cocoa Flavanols Improve Vascular Responses to Acute Mental Stress in Young Healthy Adults

Mental stress has been shown to induce cardiovascular events, likely due to its negative impact on vascular function. Flavanols, plant-derived polyphenolic compounds, improve endothelial function and blood pressure (BP) in humans, however their effects during stress are not known. This study examined the effects of acute intake of cocoa flavanols on stress-induced changes on vascular function. In a randomised, controlled, double-blind, cross-over intervention study, 30 healthy men ingested a cocoa flavanol beverage (high-flavanol: 150 mg vs. low-flavanol < 4 mg (-)-epicatechin) 1.5 h before an 8-min mental stress task). Forearm blood flow (FBF), BP, and cardiovascular activity were assessed pre- and post-intervention, both at rest and during stress. Endothelial function (brachial flow-mediated dilatation, FMD) and brachial BP were measured before the intervention and 30 and 90 min post-stress. FMD was impaired 30 min post-stress, yet high-flavanol cocoa attenuated this decline and remained significantly higher compared to low-flavanol cocoa at 90 min post-stress. High-flavanol cocoa increased FBF at rest and during stress. Stress-induced cardiovascular and BP responses were similar in both conditions. Flavanols are effective at counteracting mental stress-induced endothelial dysfunction and improving peripheral blood flow during stress. These findings suggest the use of flavanol-rich dietary strategies to protect vascular health during stress.

Anthocyanin-Rich New Zealand Blackcurrant Extract Supports the Maintenance of Forearm Blood-Flow During Prolonged Sedentary Sitting

Objectives: We examined the acute effects of anthocyanin-rich New Zealand blackcurrant extract and a placebo on hemodynamics during 120 min of sedentary sitting in healthy males. Additionally, we investigated whether changes in resting hemodynamics altered repeated isometric hand-grip exercise performance and post exercise forearm blood flow (FBF). Methods: Ten healthy males completed two trials during which they ingested either blackcurrant extract (1.87 mg total anthocyanins/kg bodyweight) or placebo powder. Heart rate, blood pressure and forearm blood flow were measured, and venous blood was sampled, prior to and 30, 60, 90 and 120 min-post ingestion. Participants remained seated for the duration of each trial. At 120 min post-ingestion participants completed as many repetitions of isometric hand-grip contractions as possible. Results: Heart rate, blood pressure and mean arterial pressure changed over time (all p < 0.001) but did not differ between treatments. A treatment x time interaction for FBF (p = 0.025) and forearm vascular resistance (FVR) (p = 0.002) was found. No difference in the number of isometric hand-grip contractions was observed between treatments (p = 0.68) nor was there any treatment x time interaction in post-exercise FBF (p = 0.997). Plasma endothelin-1 (p = 0.023) and nitrate (p = 0.047) changed over time but did not differ between treatments (both p > 0.1). Plasma nitrite did not change over time (p = 0.732) or differ between treatments (p = 0.373). Conclusion: This study demonstrated that acute ingestion of a single dose of blackcurrant extract maintained FBF and FVR during an extended period of sitting; however, this did not influence exercise performance during hand-grip exercise.

The Effects of Machine-Weight and Free-Weight Resistance Exercise on Hemodynamics and Vascular Function

The purpose of this study was to examine hemodynamic and vascular responses between machine-weight and free-weight exercise. Resistance-trained individuals were assigned to a machine-weight (n = 13) or free-weight (n = 15) group. Groups completed two visits consisting of their assigned exercise condition and a control (CON). A 2 × 2 × 3 repeated measures ANOVA was used to test the effects of group across condition and time on the hemodynamic parameters [cardiac output (CO), heart rate (HR), total peripheral resistance (TPR), mean arterial pressure (MAP), and stroke volume (SV)]. A 2 × 2 × 2 repeated measures ANOVA was used to test the effects of group across condition and time on the hemodynamic variable, forearm vascular conductance (FVC), as well as on vascular measures [forearm blood flow (FBF), blood flow peak, and total reactive hyperemia (RH)]. Main effects were analyzed using pairwise comparisons. The results of the present study demonstrate that both machine-weight and free-weight exercise produce similar (p > 0.05) alterations in hemodynamics and vascular function. Specifically, during recovery both groups demonstrated significant (p ≤ 0.05) increases in measures of hemodynamics such as CO, HR and FVC, as well as significant (p ≤ 0.05) decreases in TPR, MAP, and SV. Measures of vascular function such as FBF, blood flow peak, and total RH were also significantly (p ≤ 0.05) increased during recovery. Therefore, this study suggests that either machine weight or free-weight exercise may induce acute hemodynamic and vascular benefits, which may reduce the risk of cardiovascular disease (CVD) and CVD events.

Greater post-contraction hyperaemia below vs. above heart level: the role of active vasodilatation vs. passive mechanical distension of arterioles

KEY POINTS

The immediate increase in skeletal muscle blood flow following contraction is greater when the contracting muscle is below vs. above heart level. This has been attributed to muscle pump-mediated venous emptying and subsequent widening of the arterial to venous pressure gradient, which can occur below but not above heart level. However, alternative explanations could include greater rapid onset vasodilatation and/or transmural pressure-mediated mechanical distension of resistance vessels, but these remain unexplored. We demonstrate that active vasodilatation is not responsible for greater post-contraction hyperaemia below the heart. Instead, an increased transmural pressure-mediated mechanical distension of resistance vessels is a key mechanism responsible for this phenomenon. Our findings establish the importance of considering/accounting for local mechanical arteriolar distension effects when investigating exercise hyperaemia. They also inform the application of exercise for rehabilitative purposes and prompt investigation into whether arteriolar distension accompanying vasodilatation is reduced with diseases or ageing, thereby compromising exercising muscle perfusion.

ABSTRACT

We tested the hypotheses that increased post-contraction hyperaemia in higher (H; below heart) vs. lower (L; above heart) transmural pressure conditions is due to (1) greater active vasodilatation or (2) greater transmural pressure-mediated arteriolar distension. Participants (n = 20, 12 male, 8 female; combined mean age 24.5 ± 2 years) performed a 2 s isometric handgrip contraction, where arm position was maintained within or changed between H and L during contraction, resulting in four starting-finishing arm position conditions (LL, HL, LH, HH). Post-contraction forearm blood flow (echo and Doppler ultrasound) was higher with contraction release in H vs. L environments (P < 0.05). However, contraction initiated in H did not result in greater vasodilatation (forearm vascular conductance; FVC) than contraction initiated in L, regardless of contraction release condition (peak FVC: LL 217 ± 104 vs. HL 204 ± 92 ml min^-1 (100 mmHg)^-1 , P = 0.313, LH 229 ± 8 vs. HH 225 ± 85 ml min^-1 (100 mmHg)^-1 , P = 0.391; first post-contraction cardiac cycle FVC: same comparisons, both P = 0.317). However, FVC of the first post-contraction cardiac cycle was greater for contractions released in H vs. L regardless of pre-contraction condition (LL 106 ± 67 vs. LH 152 ± 76 ml min^-1 (100 mmHg)^-1 , P < 0.05; HL 80 ± 51 vs. HH 119 ± 58 ml min^-1 (100 mmHg)^-1 , P < 0.05). These findings refute the hypothesis that greater hyperaemia following a single contraction in higher transmural pressure conditions is due to greater active vasodilatation. Instead, our findings reveal a key role for increased transmural pressure-mediated mechanical distension of arterioles in creating a greater increase in vascular conductance for a given active vasodilatation following skeletal muscle contraction.

Microvascular capillary assessment in relation to forearm blood flow

OBJECTIVE

To study whether vascular reactivity as assessed by the methods forearm blood flow (FBF) and postocclusive reactive hyperaemia (PRH) in the nail fold was related as a measure of endothelium-dependent vasodilation in the microcirculation.

METHODS

Microvascular reactivity was assessed in forearm blood flow and in the nail fold by vital capillaroscopy of individual microvessels as postocclusive reactive hyperaemia. Vascular reactivity was assessed at baseline (n = 25) as well as after infusion of acetylcholine and of sodium nitroprusside (n = 13). We also performed a multivariate regression analysis to assess whether forearm blood flow or flow-mediated dilatation related to postocclusive reactive hyperaemia.

RESULTS

This study showed a distinct microvascular response to both acetylcholine (endothelium-dependent vasodilation) and sodium nitroprusside (endothelium-independent vasodilation) during forearm blood flow assessment and postocclusive reactive hyperaemia assessment in the nail fold (n = 13). These changes were inversely related (r- = -0·57; P<0·05).

CONCLUSIONS

Forearm blood flow was inversely correlated to postocclusive reactive hyperaemia. Postocclusive reactive hyperaemia was shortened after infusion with both acetylcholine and sodium nitroprusside. This occurred in parallel with the expected increase in forearm blood flow, conceivably reflecting that both methods can be used to assess endothelium-dependent vasodilation in the microcirculation.

Vascular Response During Mental Stress in Sedentary and Physically Active Patients With Obstructive Sleep Apnea

STUDY OBJECTIVES

To compare vascular function of sedentary (SED) versus physically active (ACTIVE) patients with obstructive sleep apnea (OSA) during rest and mental stress.

METHODS

Patients with untreated OSA without other comorbidities were classified into SED and ACTIVE groups according to the International Physical Activity Questionnaire. Blood pressure (BP), heart rate (HR), forearm blood flow (FBF) (plethysmography), and forearm vascular conductance (FVC = FBF / mean BP × 100) were continuously measured at rest (4 minutes) followed by 3 minutes of mental stress (Stroop Color Word Test).

RESULTS

We studied 40 patients with OSA (men = 24, age = 50 ± 1 years, body mass index = 29.3 ± 0.5 kg/m², apnea-hypopnea index = 39.3 ± 4 events/h). Leisure time physical activity domain in SED (n = 19) and ACTIVE (n = 21) was 20 ± 8 and 239 ± 32 min/wk, (P < .05). Baseline profile and perception of stress were similar in both groups. Baseline FBF (3.5 ± 0.2 mL/min/100 mL versus 2.4 ± 0.14 mL/min/100 mL) and FVC (3.5 ± 0.2 U versus 2.3 ± 0.1 U) were significantly lower in the SED group than in the ACTIVE group, respectively (P < .05). HR and BP increased similarly during mental stress test in both groups. Changes during mental stress in FBF (0.65 ± 0.12 versus 1.04 ± 0.12) and FVC (0.58 ± 0.11 versus 0.99 ± 0.11) were significantly lower in the SED group than in the ACTIVE group, respectively (P < .05). There was a significant correlation between leisure time physical activity and FBF (r = .57, P < .05) and FVC (r = .48, P < .05) during mental stress.

CONCLUSIONS

The vascular response among patients with OSA is influenced by the level of physical activity. A high level of physical activity may partially protect against the cardiovascular dysfunction associated with OSA.

Blue light exposure decreases systolic blood pressure, arterial stiffness, and improves endothelial function in humans

AIMS

Previous studies have shown that ultraviolet light can lead to the release of nitric oxide from the skin and decrease blood pressure. In contrast to visible light the local application of ultraviolet light bears a cancerogenic risk. Here, we investigated whether whole body exposure to visible blue light can also decrease blood pressure and increase endothelial function in healthy subjects.

METHODS

In a randomised crossover study, 14 healthy male subjects were exposed on 2 days to monochromatic blue light or blue light with a filter foil (control light) over 30 minutes. We measured blood pressure (primary endpoint), heart rate, forearm vascular resistance, forearm blood flow, endothelial function (flow-mediated dilation), pulse wave velocity and plasma nitric oxide species, nitrite and nitroso compounds (secondary endpoints) during and up to 2 hours after exposure.

RESULTS

Blue light exposure significantly decreased systolic blood pressure and increased heart rate as compared to control. In parallel, blue light significantly increased forearm blood flow, flow-mediated dilation, circulating nitric oxide species and nitroso compounds while it decreased forearm vascular resistance and pulse wave velocity.

CONCLUSION

Whole body irradiation with visible blue light at real world doses improves blood pressure, endothelial function and arterial stiffness by nitric oxide released from photolabile intracutanous nitric oxide metabolites into circulating blood.

Ticagrelor mitigates ischaemia-reperfusion induced vascular endothelial dysfunction in healthy young males - a randomized, single-blinded study

AIMS

Animal data suggest that ticagrelor but not clopidogrel protects against tissue injury. It is unclear if this effect of ticagrelor is also detectable in humans. We studied the effect of ticagrelor and clopidogrel at standard clinical doses on endothelial dysfunction in an experimental model of forearm vascular ischaemia-reperfusion (IR) injury.

METHODS

In a randomized, single-blinded trial, 24 subjects underwent forearm blood flow (FBF) measurements in response to the endothelium-dependent vasodilator acetylcholine (ACh) and to glyceryltrinitrate (GTN; endothelium-independent) before and after a 20 min forearm ischaemia. FBF reactivity was assessed after an oral loading dose of ticagrelor or clopidogrel and after 14 days of regular intake of maintenance doses of the study medicines. In addition, the effect on platelet inhibition was evaluated using multiple electrode aggregometry.

RESULTS

ACh-induced vasodilation was impaired during reperfusion and not completely normalized by acute or chronic treatment with ticagrelor or clopidogrel (post- vs. pre-ischaemia). However, ticagrelor mitigated endothelial dysfunction compared to clopidogrel after loading (FBF ACh_AUC ratio post- vs. pre-ischaemia: 0.83 [0.70; 0.96] vs. 0.64 [0.56; 0.72]; P = 0.024) and after chronic administration (FBF ACh_AUC ratio: 0.86 [0.71; 1.00] vs. 0.66 [0.55; 0.77]; P = 0.027). As expected, GTN-induced vasodilation was not affected by ischaemia. Ticagrelor or clopidogrel treatment inhibited platelet activation to a similar degree.

CONCLUSION

Our data indicate that ticagrelor treatment exerts a greater vascular salutary effect than clopidogrel during reperfusion after an acute vascular occlusion. IR-induced vascular injury cannot be prevented completely by administration of these antiplatelet agents at standard clinical doses.

Regular physical exercise improves cardiac autonomic and muscle vasodilatory responses to isometric exercise in healthy elderly

The objective of this study was to evaluate cardiac autonomic control and muscle vasodilation response during isometric exercise in sedentary and physically active older adults. Twenty healthy participants, 10 sedentary and 10 physically active older adults, were evaluated and paired by gender, age, and body mass index. Sympathetic and parasympathetic cardiac activity (spectral and symbolic heart rate analysis) and muscle blood flow (venous occlusion plethysmography) were measured for 10 minutes at rest (baseline) and during 3 minutes of isometric handgrip exercise at 30% of the maximum voluntary contraction (sympathetic excitatory maneuver). Variables were analyzed at baseline and during 3 minutes of isometric exercise. Cardiac autonomic parameters were analyzed by Wilcoxon and Mann–Whitney tests. Muscle vasodilatory response was analyzed by repeated-measures analysis of variance followed by Tukey’s post hoc test. Sedentary older adults had higher cardiac sympathetic activity compared to physically active older adult subjects at baseline (63.13±3.31 vs 50.45±3.55 nu, P=0.02). The variance (heart rate variability index) was increased in active older adults (1,438.64±448.90 vs 1,402.92±385.14 ms, P=0.02), and cardiac sympathetic activity (symbolic analysis) was increased in sedentary older adults (5,660.91±1,626.72 vs 4,381.35±1,852.87, P=0.03) during isometric handgrip exercise. Sedentary older adults showed higher cardiac sympathetic activity (spectral analysis) (71.29±4.40 vs 58.30±3.50 nu, P=0.03) and lower parasympathetic modulation (28.79±4.37 vs 41.77±3.47 nu, P=0.03) compared to physically active older adult subjects during isometric handgrip exercise. Regarding muscle vasodilation response, there was an increase in the skeletal muscle blood flow in the second (4.1±0.5 vs 3.7±0.4 mL/min per 100 mL, P=0.01) and third minute (4.4±0.4 vs 3.9±0.3 mL/min per 100 mL, P=0.03) of handgrip exercise in active older adults. The results indicate that regular physical activity improves neurovascular control of muscle blood flow and cardiac autonomic response during isometric handgrip exercise in healthy older adult subjects.

Cyclo-oxygenase-2 inhibition and endothelium-dependent vasodilation in younger vs. older healthy adults

AIM

A major feature of endothelial dysfunction is reduced endothelium-dependent vasodilation, which in ageing may be due to decreased production of endothelial prostacyclin, or nitric oxide (NO), or both.

METHOD

We tested this hypothesis in 12 younger (age 18-38 years, six women) and 12 older healthy adults (age 55-73 years, six post-menopausal women). Endothelium-dependent vasodilation was assessed by the forearm vascular conductance (FVC) response to intra-arterial acetylcholine (ACh) (0.5, 1.0, 2.0, 4.0 μg dl(-1) forearm tissue min(-1) ) before and 90 min after inhibition of the enzyme cyclo-oxygenase-2 (COX-2) with oral celecoxib (400 mg), followed by the addition of endothelial NO synthase inhibition with intra-arterial N(G) -monomethyl-l arginine acetate (L-NMMA).

RESULTS

Ageing was associated with a significantly reduced FVC response to ACh (P = 0.009, age-by-dose interaction; highest dose FVC ± SEM in ageing: 11.2 ± 1.4 vs. younger: 17.7 ± 2.4 units, P = 0.02). Celecoxib did not reduce resting FVC or the responses to ACh in any group. L-NMMA significantly reduced resting FVC and the responses to ACh in all groups, and absolute FVC values following L-NMMA were similar between groups.

CONCLUSION

In healthy normotensive younger and older adults, there is minimal contribution of prostacyclin to ACh-mediated vasodilation, yet the NO component of vasodilation is reduced with ageing. In the clinical context, these findings suggest that acute administration of medications that inhibit prostacyclin (i.e. COX-2 inhibitors) evoke modest vascular consequences in healthy persons. Additional studies are necessary to test whether chronic use of COX-2 medications reduces endothelium dependent vasodilation in older persons with or without cardiovascular risk factors.

Increment of body mass index is positively correlated with worsening of endothelium-dependent and independent changes in forearm blood flow

Obesity is associated with the impairment of endothelial function leading to the initiation of the atherosclerotic process. As obesity is a multiple grade disease, we have hypothesized that an increasing impairment of endothelial and vascular smooth muscle cell functions occurs from lean subjects to severe obese ones, creating a window of opportunities for preventive measures. Thus, the present study was carried out to investigate the grade of obesity in which endothelial dysfunction can be detected and if there is an increasing impairment of endothelial and vascular smooth muscle cell functions as body mass index increases. According to body mass index, subjects were allocated into five groups: Lean controls (n = 9); Overweight (n = 11); Obese class I (n = 26); Obese class II (n = 15); Obese class III (n = 19). Endothelial and vascular smooth muscle cell functions were evaluated measuring forearm blood flow responses to increasing intra-arterial infusions of acetylcholine and sodium nitroprusside using venous occlusion plethysmography. We observed that forearm blood flow was progressively impaired from lean controls to severe obese and found no significant differences between Lean controls and Overweight groups. Known determinants of endothelial dysfunction, such as inflammatory response, insulin resistance, and diagnosis of metabolic syndrome, did not correlate with forearm blood flow response to vasodilators. Moreover, several risk factors for atherosclerosis were excluded as independent predictors after confounder-adjusted analysis. Our data suggests that obesity per se could be sufficient to promote impairment of vascular reactivity, that obesity class I is the first grade of obesity in which endothelial dysfunction can be detected, and that body mass index positively correlates with the worsening of endothelium-dependent and independent changes in forearm blood flow.

Influence of habitual high dietary fat intake on endothelium-dependent vasodilation

High-fat diets are associated with an increased risk of cardiovascular disease. A potential underlying mechanism for the increased cardiovascular risk is endothelial dysfunction. Nitric oxide (NO)-mediated endothelium-dependent vasodilation is critical in the regulation of vascular tone and overall vascular health. The aim of this study was to determine the influence of dietary fat intake on endothelium-dependent vasodilation. Forty-four middle-aged and older sedentary, healthy adults were studied: 24 consumed a lower fat diet (LFD; 29% ± 1% calories from fat) and 20 consumed a high-fat diet (HFD; 41% ± 1% calories from fat). Four-day diet records were used to assess fat intake, and classifications were based on American Heart Association guidelines (<35% of total calories from fat). Forearm blood flow (FBF) responses to acetylcholine, in the absence and presence of the endothelial NO synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA), as well as responses to sodium nitroprusside were determined by plethysmography. The FBF response to acetylcholine was lower (∼15%; P < 0.05) in the HFD group (4.5 ± 0.2 to 12.1 ± 0.8 mL/100 mL tissue/min) than in the LFD group (4.6 ± 0.2 to 14.4 ± 0.6 mL/100 mL tissue/min). L-NMMA significantly reduced the FBF response to acetylcholine in the LFD group (∼25%) but not in the HFD group. There were no differences between groups in the vasodilator response to sodium nitroprusside. These data indicate that a high-fat diet is associated with endothelium-dependent vasodilator dysfunction due, in part, to diminished NO bioavailability. Impaired NO-mediated endothelium-dependent vasodilation may contribute to the increased cardiovascular risk with high dietary fat intake.

Effect of vitamin C on hyperoxia-induced vasoconstriction in exercising skeletal muscle

Hyperoxia can cause substantial reductions in peripheral and coronary blood flow at rest and during exercise, which may be caused by reactive oxygen species (ROS) generated during hyperoxia. The aim of this study was to investigate the role of ROS in hyperoxia-induced reductions in skeletal muscle blood flow during forearm exercise. We hypothesized that infusion of vitamin C would abolish the effects of hyperoxia on the forearm blood flow (FBF) responses to exercise. Twelve young healthy adults performed rhythmic forearm handgrip exercise (10% of maximum voluntary contraction for 5 min) during normoxia and hyperoxia. For each condition, two trials were conducted with intra-arterial administration of saline or vitamin C. FBF was measured using Doppler ultrasound. During hyperoxia with saline, FBF and forearm vascular conductance (FVC) were 86.3 ± 5.1 and 86.8 ± 5.2%, respectively, of the normoxic values (100%) (P < 0.05). During vitamin C, hyperoxic FBF and FVC responses were 90.9 ± 4.2 and 90.9 ± 4.1%, respectively, of the normoxic values (P = 0.57 and 0.59). Subjects were then divided into three subgroups based on their percent decrease in FBF (>20, 10-20, and <10%) during hyperoxia. In the subgroup that demonstrated the greatest hyperoxia-induced changes (>20%), FBF and FVC during hyperoxia were 67.1 ± 4.0 and 66.8 ± 3.6%, respectively, of the normoxic values. Vitamin C abolished these effects on FBF and FVC with values that were 102.0 ± 5.2 and 100.8 ± 6.1%, respectively. However, vitamin C had no effect in the other two subgroups. This analysis is consistent with the idea that ROS generation blunts the FBF responses to exercise in the subjects most affected by hyperoxia.

Histamine-induced vasodilatation in the human forearm vasculature

AIM

To investigate the mechanism of action of intra-arterial histamine in the human forearm vasculature.

METHODS

Three studies were conducted to assess changes in forearm blood flow (FBF) using venous occlusion plethysmography in response to intra-brachial histamine. First, the dose-response was investigated by assessing FBF throughout a dose-escalating histamine infusion. Next, histamine was infused at a constant dose to assess acute tolerance. Finally, a four way, double-blind, randomized, placebo-controlled crossover study was conducted to assess FBF response to histamine in the presence of H1 - and H2 -receptor antagonists. Flare and itch were assessed in all studies.

RESULTS

Histamine caused a dose-dependent increase in FBF, greatest with the highest dose (30 nmol min(-1) ) infused [mean (SEM) infused arm vs. control: 26.8 (5.3) vs. 2.6 ml min(-1)  100 ml(-1) ; P < 0.0001]. Dose-dependent flare and itch were demonstrated. Acute tolerance was not observed, with an increased FBF persisting throughout the infusion period. H2 -receptor antagonism significantly reduced FBF (mean (95% CI) difference from placebo at 30 nmol min(-1) histamine: -11.9 ml min(-1)  100 ml(-1) (-4.0, -19.8), P < 0.0001) and flare (mean (95% CI) difference from placebo: -403.7 cm(2) (-231.4, 576.0), P < 0.0001). No reduction in FBF or flare was observed in response to the H1 -receptor antagonist. Itch was unaffected by the treatments. Histamine did not stimulate vascular release of tissue plasminogen activator or von Willebrand factor.

CONCLUSION

Histamine causes dose-dependent vasodilatation, flare and itch in the human forearm. H2 -receptors are important in this process. Our results support further exploration of combined H1 - and H2 -receptor antagonist therapy in acute allergic syndromes.

Ascorbic acid does not enhance hypoxia-induced vasodilation in healthy older men

In response to hypoxia, a net vasodilation occurs in the limb vasculature in young healthy humans and this is referred to as “hypoxia‐induced vasodilation”. We performed two separate experiments to determine (1) if hypoxia‐induced forearm vasodilation is impaired in older men (n = 8) compared to young men (n = 7) and (2) if acute systemic infusion of ascorbic acid would enhance hypoxia‐induced vasodilation in older men (n = 8). Heart rate, mean arterial pressure, oxygen saturation, minute ventilation, forearm vascular conductance (FVC, Doppler ultrasound), and cutaneous vascular conductance (CVC, laser Doppler flowmetry) were recorded continuously while subjects breathed 10% oxygen for 5 min. Changes from baseline were compared between groups and between treatments. The older adults had a significantly attenuated increase in FBF (13 ± 4 vs. 30 ± 7%) and FVC (16 ± 4 vs. 30 ± 7%) in response to 5 min of hypoxia. However, skin blood flow responses were comparable between groups (young: 35 ± 9, older: 30 ± 6%). In Experiment 2, FVC responses to 5 min of breathing 10% oxygen were not significantly different following saline (3 ± 10%) and ascorbic acid (8 ± 10%) in the older men. Ascorbic acid also had no physiological effects in the young men. These findings advance our basic understanding of how aging influences vascular responses to hypoxia and suggest that, in healthy humans, hypoxia‐induced vasodilation is not restrained by reactive oxygen species.

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In Experiment 1, heart rate (HR), mean arterial pressure (MAP), forearm vascular conductance (FVC), and forearm cutaneous vascular conductance (CVC) were measured in response to 5 min of continuous hypoxia (10% oxygen) in young men (black diamonds) and older men (white squares). In Experiment 2, older men breathed continuous hypoxia after receiving normal saline solution (NSS, white squares) and ascorbic acid (Vit C, black squares). These findings advance our basic understanding of how aging influences vascular responses to hypoxia and suggest that, in healthy humans, hypoxia‐induced vasodilation is not restrained by reactive oxygen species.

Acute cyclooxygenase inhibition does not alter muscle sympathetic nerve activity or forearm vasodilator responsiveness in lean and obese adults

Obesity is often characterized by chronic inflammation that may contribute to increased cardiovascular risk via sympathoexcitation and decreased vasodilator responsiveness. We hypothesized that obese individuals would have greater indices of inflammation compared with lean controls, and that cyclooxygenase inhibition using ibuprofen would reduce muscle sympathetic nerve activity (MSNA) and increase forearm blood flow in these subjects. We measured MSNA, inflammatory biomarkers (C‐reactive protein [CRP] and Interleukin‐6 [IL‐6]), and forearm vasodilator responses to brachial artery acetylcholine and sodium nitroprusside in 13 men and women (7 lean; 6 obese) on two separate study days: control (CON) and after 800 mg ibuprofen (IBU). CRP (1.7 ± 0.4 vs. 0.6 ± 0.3 mg/L; P < 0.05) and IL‐6 (4.1 ± 1.5 vs. 1.0 ± 0.1pg/mL; P < 0.05) were higher in the obese group during CON and tended to decrease with IBU (IL‐6: P < 0.05; CRP: P = 0.14). MSNA was not different between groups during CON (26 ± 4 bursts/100 heart beats (lean) versus 26 ± 4 bursts/100 heart beats (obese); P = 0.50) or IBU (25 ± 4 bursts/100 heart beats (lean) versus 30 ± 5 bursts/100 heart beats (obese); P = 0.25), and was not altered by IBU. Forearm vasodilator responses were unaffected by IBU in both groups. In summary, an acute dose of ibuprofen did not alter sympathetic nerve activity or forearm blood flow responses in healthy obese individuals, suggesting that the cyclooxygenase pathway is not a major contributor to these variables in this group.

Obesity is often characterized by chronic inflammation that may contribute to increased cardiovascular risk via sympathoexcitation. However, an acute dose of the cyclooxygenase inhibitor ibuprofen did not alter blood pressure or muscle sympathetic nerve activity in lean and obese humans.

A polymorphism at IGF1 locus is associated with carotid intima media thickness and endothelium-dependent vasodilatation

OBJECTIVE

Whether IGF-1 has a protective or a detrimental role in vascular homeostasis remains unsettled. There is evidence that the C/T polymorphism rs35767 near the promoter region of the IGF1 gene located in chromosome 12 is associated with plasma IGF-1 levels. We investigated the effects of this polymorphism on circulating IGF-1 levels, carotid intima media thickness (cIMT) and endothelial-dependent vasodilation.

METHODS

Two samples of adult nondiabetic Whites were studied. Sample 1 comprised 1124 individuals in whom cIMT was measured by ultrasonography. Sample 2 included 162 drug-naïve hypertensive individuals in whom endothelium-dependent and endothelium-independent vasodilation were assessed by intra-arterial infusion of acetylcholine (ACh), and sodium nitroprusside (SNP), respectively. IGF-1 was determined by chemiluminescent immunoassay. rs35767 polymorphism was screened using a TaqMan allelic discrimination assay.

RESULTS

In sample 1, IGF-1 levels were higher in subjects carrying the T allele compared with CC carriers (178 ± 78 vs. 166 ± 60 ng/mL, respectively; P = 0.007 adjusted for age, gender, and BMI). cIMT was lower in subjects carrying the T allele compared with CC carriers (0.71 ± 0.20 vs. 0.76 ± 0.22 mm, respectively; P < 0.0001 adjusted for age, gender, and BMI). In sample 2, maximally ACh-stimulated forearm blood flow was higher in subjects carrying the T allele compared with CC carriers (343 ± 191 vs. 281 ± 125%, respectively; P = 0.02 adjusted for age, gender, and BMI).

CONCLUSION

Subjects carrying the T allele exhibited significantly higher levels of circulating IGF-1, lower values of cIMT, and higher endothelium-dependent vasodilatation compared with CC carriers. These findings support the idea that IGF-1 plays a role in the pathogenesis of atherosclerosis.

Effect of oxidative stress on sympathetic and renal vascular responses to ischemic exercise

Reactive oxygen species (ROS), produced acutely during skeletal muscle contraction, are known to stimulate group IV muscle afferents and accentuate the exercise pressor reflex (EPR) in rodents. The effect of ROS on the EPR in humans is unknown. We conducted a series of studies using ischemic fatiguing rhythmic handgrip to acutely increase ROS within skeletal muscle, ascorbic acid infusion to scavenge free radicals, and hyperoxia inhalation to further increase ROS production. We hypothesized that ascorbic acid would attenuate the EPR and that hyperoxia would accentuate the EPR. Ten young healthy subjects participated in two or three experimental trials on separate days. Beat-by-beat measurements of heart rate (HR), mean arterial pressure (MAP), muscle sympathetic nerve activity (MSNA), and renal vascular resistance index (RVRI) were measured and compared between treatments (saline and ascorbic acid; room air and hyperoxia). At fatigue, the reflex increases in MAP (31 ± 3 versus 29 ± 2 mmHg), HR (19 ± 3 versus 20 ± 3 bpm), MSNA burst rate (21 ± 4 versus 23 ± 4 burst/min), and RVRI (39 ± 12 versus 44 ± 13%) were not different between saline and ascorbic acid. Relative to room air, hyperoxia did not augment the reflex increases in MAP, HR, MSNA, or RVRI in response to exercise. Muscle metaboreflex activation and time/volume control experiments similarly showed no treatment effects. While contrary to our initial hypotheses, these findings suggest that ROS do not play a significant role in the normal reflex adjustments to ischemic exercise in young healthy humans.

Sympathetic activation increases NO release from eNOS but neither eNOS nor nNOS play an essential role in exercise hyperemia in the human forearm

Nitric oxide (NO) release from endothelial NO synthase (eNOS) and/or neuronal NO synthase (nNOS) could be modulated by sympathetic nerve activity and contribute to increased blood flow after exercise. We examined the effects of brachial-arterial infusion of the nNOS selective inhibitor S-methyl-l-thiocitrulline (SMTC) and the nonselective NOS inhibitor N(G)-monomethyl-l-arginine (l-NMMA) on forearm arm blood flow at rest, during sympathetic activation by lower body negative pressure, and during lower body negative pressure immediately after handgrip exercise. Reduction in forearm blood flow by lower body negative pressure during infusion of SMTC was not significantly different from that during vehicle (-28.5 ± 4.02 vs. -34.1 ± 2.96%, respectively; P = 0.32; n = 8). However, l-NMMA augmented the reduction in forearm blood flow by lower body negative pressure (-44.2 ± 3.53 vs. -23.4 ± 5.71%; n = 8; P < 0.01). When lower body negative pressure was continued after handgrip exercise, there was no significant effect of either l-NMMA or SMTC on forearm blood flow immediately after low-intensity exercise (P = 0.91 and P = 0.44 for l-NMMA vs. saline and SMTC vs. saline, respectively; each n = 10) or high-intensity exercise (P = 0.46 and P = 0.68 for l-NMMA vs. saline and SMTC vs. saline, respectively; each n = 10). These results suggest that sympathetic activation increases NO release from eNOS, attenuating vasoconstriction. Dysfunction of eNOS could augment vasoconstrictor and blood pressure responses to sympathetic activation. However, neither eNOS nor nNOS plays an essential role in postexercise hyperaemia, even in the presence of increased sympathetic activation.

Influence of demographic and metabolic variables on forearm blood flow and vascular conductance in individuals without overt heart disease

PURPOSE

Vascular reactivity is involved in the regulation of vascular function either in normal conditions or in the pathophysiology of cardiovascular diseases. We tested the hypothesis that vascular reactivity evaluated by forearm blood flow may vary according to demographic and metabolic variables in a cohort of individuals without any evidence of heart disease after clinical examination.

SUBJECTS AND METHODS

We studied 186 individuals (mean age 41.4 years, standard deviation 13.1 years; 95 (51%) men and 91 (49%) women. We investigated forearm blood flow and vascular conductance with venous occlusion plethysmography at baseline, during handgrip isometric exercise and during the recovery phase. Demographic and laboratory data were collected. Statistical analysis was performed with mixed linear models appropriate for repeated measurements.

RESULTS

Mean forearm blood flow values in the different study conditions ranged between 1.7+/-0.47 mL.min(-1).100 mL(-1) of tissue and 2.82+/-1.13 mL.min(-1).100 mL(-1) of tissue. Forearm blood flow was higher in men than in women (P<0.005) and increased as the heart rate increased during handgrip maneuver (P<0.0001). Serum triglyceride levels were inversely related to forearm blood flow at baseline, during isometric exercise and recovery phase (P=0.0209). Body mass index was inversely related to forearm vascular conductance at baseline, during isometric exercise and recovery phase (P=0.0223).

CONCLUSION

Our findings suggest that forearm blood flow and vascular conductance as a surrogate of the vascular function may be influenced by gender, heart rate, serum triglyceride levels and body mass index in individuals without overt heart disease.

Acute effect of a single high-fat meal on forearm blood flow, blood pressure and heart rate in healthy male Asians and Caucasians: a pilot study

Research has shown that ingestion of a single high-fat (HF) meal causes postprandial lipemia and produces a reduced brachial artery blood flow response to vascular occlusion in Caucasians. However, the forearm BF response to occlusion in Caucasian and Asian populations after a single HF meal has not been compared. Eleven healthy male Asians, mean age 26.4 (+/- 4.2) years, height 174.2 (+/- 7.4) cm, and weight 73.8 (+/- 5.7) kg and eight Caucasians, mean age 26.8 (+/- 4.6) years, height 182.9 (+/- 5.9) cm, and weight 82.8 (+/- 4.8) kg were studied. A randomized cross-over study design was used with a HF (50.1 g total fat) or low-fat (LF) (5.1 g total fat) test meal 1 week apart. Forearm blood flow was measured over a 2-minute period following a 4-minute occlusion (FBFO) at 2 and 4 hours following ingestion of a test meal. This study found that FBFO was significantly attenuated in Asians (19.3%; p = 0.09) compared to Caucasians after the ingestion of a HF meal. When comparing LF vs. HF meals in Asians, the FBFO were 336.9 ml/100 ml tissue/ minute and 240.8 ml/100 ml tissue/minute, respectively (p = 0.02), whereas in Caucasians, the FBFO were 344.8 ml/100 ml tissue/minute and 287.4 ml/100 ml tissue/minute, respectively. It appears Asians have a more sensitive response to a single HF meal which may be explained, in part, by genotypic variation. These findings suggest that a single HF meal may contribute to the detrimental effects on vascular health in Asian males and raises speculation regarding the cumulative impact of a chronic HF diet in this population.

Effects of exercise training in patients with chronic heart failure and sleep apnea

STUDY OBJECTIVES

To test the effects of exercise training on sleep and neurovascular control in patients with systolic heart failure with and without sleep disordered breathing.

DESIGN

Prospective interventional study.

SETTING

Cardiac rehabilitation and exercise physiology unit and sleep laboratory.

PATIENTS

Twenty-five patients with heart failure, aged 42 to 70 years, and New York Heart Association Functional Class I-III were divided into 1 of 3 groups: obstructive sleep apnea (n=8), central sleep apnea (n=9) and no sleep apnea (n=7). INTERVENTIONS Four months of no-training (control) followed by 4 months of an exercise training program (three 60-minute, supervised, exercise sessions per week).

MEASURES AND RESULTS

Sleep (polysomnography), microneurography, forearm blood flow (plethysmography), peak VO2, and quality of life were evaluated at baseline and at the end of the control and trained periods. No significant changes occurred in the control period. Exercise training reduced muscle sympathetic nerve activity (P < 0.001) and increased forearm blood flow (P < 0.01), peak VO2( P < 0.01), and quality of life (P < 0.01) in all groups, independent of the presence of sleep apnea. Exercise training improved the apnea-hypopnea index, minimum 0O saturation, and amount stage 3-4 sleep (P < 0.05) in patients with obstructive sleep apnea but had no significant effects in patients with central sleep apnea.

CONCLUSIONS

The beneficial effects of exercise training on neurovascular function, functional capacity, and quality of life in patients with systolic dysfunction and heart failure occurs independently of sleep disordered breathing. Exercise training lessens the severity of obstructive sleep apnea but does not affect central sleep apnea in patients with heart failure and sleep disordered breathing.

C-peptide has no effect on forearm blood flow during local hyperinsulinaemia in healthy humans

BACKGROUND

C-peptide increases forearm blood flow (FBF) in patients with Type 1 diabetes, probably by interaction with insulin, but not in healthy subjects. It is unclear if the vasodilating effect is sealed at normal fasting insulin concentrations.

METHODS

The effects of C-peptide alone and during local hyperinsulinaemia were studied in healthy young men. Subjects received intra-arterial insulin at 6 pmol min-1 (low dose) or placebo for 60 min with subsequent coinfusion of C-peptide at increasing doses of 2-60 pmol min-1 in a double-blind crossover study (n = 8). In control experiments insulin at 30 pmol min-1 (high dose) was coinfused with C-peptide (n = 3). FBF was measured by strain-gauge plethysmography.

RESULTS

Placebo had no effect on FBF (mean percentage change from baseline at 50 min -3.1%, 95% confidence interval [CI]-14.9, + 8.7). Insulin infusion slightly enhanced FBF by + 10.2% (95% CI -6.8, + 27.2; low dose) and + 17.6% (95% CI -38.8, + 74.0; high dose), respectively. The mean individual difference of the change in FBF between low-dose insulin and placebo was + 13.3% (95% CI -6.0, + 32.7; P = NS). Infusion of C-peptide increased local C-peptide concentrations from 1.8 +/- 0.1 ng ml-1 to 6.1 +/- 2.8 ng ml-1, but had no effect on FBF during placebo or hyperinsulinaemia (mean difference vs low dose insulin -16.0%, 95% CI -38.9, + 6.9).

CONCLUSION

The vasodilating effect of C-peptide seen in Type 1 diabetes is not detectable during fasting or hyperinsulinaemia in the forearm vasculature of healthy subjects. This suggests saturation of its vasodilating potency at insulin concentrations within the normal or in the supraphysiological range.

Enhanced vasodilatation to endothelin antagonism in patients with compensated cirrhosis and the role of nitric oxide

BACKGROUND AND AIMS

Patients with advanced cirrhosis have systemic vasodilatation and increased nitric oxide (NO) production despite activated vasopressor systems, including the endothelin system. The aims of this study were to assess the contribution of endogenous endothelin 1 (ET-1) and NO to the maintenance of basal forearm vascular tone in patients with preascitic cirrhosis (n=7) and in age and sex matched healthy controls (n=7).

METHODS

Using venous occlusion plethysmography, forearm blood flow (FBF) responses to subsystemic locally active intra-arterial infusion of BQ-123 (a selective endothelin type A receptor (ET(A)) receptor antagonist; 10 nmol/min) were measured before and during application of an "NO clamp": a balanced co-infusion of L-N(G)-monomethyl-arginine (a selective NO synthase inhibitor) and sodium nitroprusside (an exogenous NO donor) to block endogenous NO production and restore NO mediated basal FBF, respectively.

RESULTS

L-NMMA infusion produced a reduction in FBF (p<0.001) which was similar in both groups. Before applying the "NO clamp", BQ-123 caused an increase in FBF in both groups (p<0.001) that was greater in patients with cirrhosis (p<0.01). During the "NO clamp", BQ-123 induced vasodilatation was abolished in controls and attenuated in patients (p<0.001) but remained significantly greater in patients with cirrhosis (p<0.01).

CONCLUSIONS

These findings indicate a greater ET(A) mediated contribution of endogenous ET-1 to the maintenance of basal forearm vascular tone in patients with preascitic cirrhosis. In addition, enhanced vasodilatation to ET(A) receptor antagonism in cirrhosis cannot be entirely attributed to NO release but is likely to be related to reversal of direct ET-1 mediated tone.

Adrenomedullin (ADM) in the human forearm vascular bed: effect of neutral endopeptidase inhibition and comparison with proadrenomedullin NH2-terminal 20 peptide (PAMP)

AIMS

To compare the haemodynamic responses of proadrenomedullin N-terminal 20 peptide (PAMP) and adrenomedullin (ADM) in the forearm vascular bed of healthy male volunteers, and to investigate the role of neutral endopeptidase (NEP) in the metabolism of ADM.

METHODS

On two separate occasions, ADM (1-30 pmol x min(-1)) and PAMP (100-3000 pmol x min(-1)) were infused into the brachial artery of eight male subjects, and forearm blood flow (FBF) assessed using venous occlusion plethysmography. In a second study, eight male subjects received the same doses of ADM, co-infused with either the NEP inhibitor thiorphan (30 nmol x min(-1)) or the control vasoconstrictor noradrenaline (120 pmol x min(-1)), on separate occasions. Both studies were conducted in a double-blind, randomized manner.

RESULTS

ADM and PAMP produced a dose-dependent increase in FBF (P < or = 0.002). Based on the dose producing a 50% increase in FBF, ADM was approximately 60 times more potent than PAMP. Thiorphan and noradrenaline produced similar reductions in FBF of 14 +/- 4% (mean +/- s.e. mean) and 22 +/- 6%, respectively (P = 0.4). However, the area under the dose-response curve was significantly greater during co-infusion of ADM with thiorphan than with noradrenaline (P = 0.028), as was the maximum increase in FBF ratio (2.1 +/- 1.0 vs 1.2 +/- 0.2; P = 0.030).

CONCLUSIONS

ADM and PAMP both produce a local dose-related vasodilatation in the human forearm, but PAMP is approximately 60 times less potent than ADM. In addition, NEP inhibition potentiates the haemodynamic effects of ADM. These findings suggest that PAMP may not play a role in the physiological regulation of blood flow. However, in pathophysiological conditions such as hypertension and heart failure, NEP inhibition may exert a beneficial effect by increasing the biological activity of ADM.

Forearm reactive hyperaemia is not mediated by nitric oxide in healthy volunteers

AIMS

To determine the role of nitric oxide (NO) in forearm reactive hyperaemia in healthy human subjects.

METHODS

Ten healthy subjects aged 19-34 years underwent brachial artery cannulation. Forearm circulatory arrest was achieved by means of an upper arm cuff inflated to 200 mmHg for 5 min. The blood flow responses during reactive hyperaemia were measured using venous occlusion plethysmography following a 10 min intra-arterial infusion of 8 micromol min-1 N-monomethyl L-arginine (L-NMMA) and following matching placebo administered in random order. Results were analysed by repeated measures anova and t-tests.

RESULTS

L-NMMA resulted in a significant reduction of basal forearm blood flow indicating inhibition of basal NO release (P=0.005). There was no significant difference between the blood flow responses during reactive hyperaemia following L-NMMA and placebo (P=0.97).

CONCLUSIONS

Nitric oxide production does not make a significant contribution to the vasodilatation associated with reactive hyperaemia in the human forearm.

Flow ratios to express results obtained with the human in vivo 'perfused forearm technique'

AIMS

To determine the accuracy of forearm blood flow (FBF) ratio (flow in infused arm/flow in control arm) to detect unilateral increases in forearm blood flow.

METHODS

In nine healthy male volunteers, we measured the effect of infusion of saline into the brachial artery at a rate of 2 ml/100 ml forearm min-1 on FBF ratio during control, mental arithmetic (MAR) and lower body negative pressure (LBNP) at -40 mmHg.

RESULTS

Saline infusion increased FBF ratio from baseline by 115.9+/-17.4, 82.0+/-19.0 and 159.6+/-53.3% for control, MAR and LBNP, respectively (P<0.05 for MAR vs control).

CONCLUSIONS

FBF ratio may underestimate unilateral increases in forearm blood flow during simultaneous mental arousal.

How reproducible is bilateral forearm plethysmography?

AIMS

In studies using strain-gauge forearm plethysmography to measure changes in forearm blood flow (FBF) during intra-arterial infusions of vasoactive substances, measurements are often made in both arms simultaneously and the change in ratio of the infused and control arms used to express responses. However, the reproducibility of bilateral plethysmography in this setting has not been addressed in published studies. The unilateral technique remains in use, and forearm vascular resistance (FVR), an alternative method of expressing responses, is used by some investigators. We have assessed: (a) the intra-subject variability of bilateral FBF measurements (FBF ratios) at rest, after unilateral forearm exercise, and during intra-arterial infusions of vasoconstrictor substances; (b) whether bilateral plethysmography is more reproducible than unilateral plethysmography; and (c) the reproducibility of FVR (unilateral and bilateral).

METHODS

Study 1 Nine healthy subjects attended 3 study days, 1 week apart. FBF was measured at rest and after 2 min of standardized unilateral forearm exercise; between-day intra-subject variability was expressed as coefficients of variation (CV) calculated using two-way analysis of variance (ANOVA). Study 2 Five healthy subjects attended 2 study days when FBF was measured during incremental infusions of noradrenaline (15, 30, 150, 300 pmol min[-1]) and angiotensin II (1, 5, 10, 50 pmol min[-1]); for each individual subject at each dose intra-subject variability was assessed using the difference between responses (percentage change from baseline) on days 1 and 2.

RESULTS

Study 1 At rest, intra-subject variability (CV) of baseline FBF ratios was 19% compared with 31% (left) and 39% (right) for unilateral FBF measurements. After ipsilateral exercise, unilateral FBF measurements were more reproducible (32 vs 17%) than FBF ratios; by 20 min after exercise, the previous pattern had been re-established (19 vs 27%). Intra-subject variability (CV) of baseline FVR ratio and post-exercise FVR was 14%. Study 2 Inter-quartile ranges of the differences between responses on days 1 and 2 (FBF ratios vs FBF) were: angiotensin II 14 vs 18%; noradrenaline 16 vs 27%.

CONCLUSIONS

FBF ratios are more reproducible than unilateral FBF measurements at rest (CV 19% vs 39%) and for measuring responses to intra-arterial infusions of vasoconstrictor substances. FVR may have a small reproducibility advantage. Non-experimental stimuli can cause significant and misleading changes in measured responses if unilateral measurements are used; it is therefore recommended that responses to intra-arterial infusions should be measured using bilateral forearm plethysmography with the results expressed as FBF ratios.

The peptide endothelin receptor antagonist, TAK-044, produces sustained inhibition of endothelin-1 mediated arteriolar vasoconstriction

AIMS

Endothelin-1 (ET-1) has been implicated in the pathophysiology of a number of cardiovascular diseases for which endothelin receptor antagonists are currently under clinical development. We have previously reported that systemic administration of the combined endothelin A/B receptor antagonist, TAK-044, abolishes the forearm vasoconstriction caused by intrabrachial ET-1 infusion for at least 3 h. In this study we investigated whether TAK-044 can inhibit ET-1 mediated forearm vasoconstriction for longer periods.

METHODS

Eighteen subjects were recruited to a randomized, placebo-controlled, single-blind, three-way, crossover study. Subjects were divided into three groups of six. Groups received 25 mg, 50 mg or 100 mg TAK-044 on two separate occasions, 6 and 10 h before the start of a 2 h intrabrachial infusion of ET-1 (5 pmol min(-1)). On a third occasion subjects received only placebo before intra-arterial ET-1 infusion. Forearm vasoconstriction to ET-1 was measured by venous occlusion plethysmography.

RESULTS

In the placebo phase, ET-1 caused significant, slowly-progressive local forearm vasoconstriction of approximately 30% (P<0.01) in all three groups. All three doses of TAK-044, administered at both timepoints, tended to blunt the vasoconstriction caused by ET-1. When the responses from all three groups were combined, TAK-044 significantly reduced ET-1 mediated vasoconstriction compared with placebo -9% (95% CI -15 to -3; P=0.01) at 8 h and by -9% (95% CI -17 to -2; P=0.01) 12 h after dosing.

CONCLUSIONS

TAK-044 attenuated, but did not abolish, local ET-1 mediated vasoconstriction, for up to 12 h after administration. Vasoconstriction to local intra-arterial administration of ET-1 appears to represent a safe and reproducible pharmacodynamic index of systemic endothelin receptor antagonism in humans.

Forearm endothelium-dependent vascular responses and the potassium-ATP channel

AIMS

Vasodilation to acetylcholine is mediated at least in part by endothelium-derived hyperpolarising factor (EDHF) which causes membrane hyperpolarisation by activating potassium channels. It is however uncertain which potassium channel mediates this effect. The aim of this study was to determine the role of the potassium-ATP (K(+)-ATP) channel in mediating endothelium-dependent vascular responses to acetylcholine.

METHODS

In 10 healthy volunteers acetylcholine, an endothelium-dependent vasodilator, and sodium nitroprusside as a control assessing endothelium-independent vasodilatation were infused into the non-dominant brachial artery. Forearm blood flow (FBF) in response to each dose was measured by strain-gauge venous occlusion plethysmography. The K(+)-ATP channel blocker glipizide (2.5 mg) was then administered orally. After 45 min the infusions with FBF measurements were repeated.

RESULTS

Acetylcholine (P < 0.01) and sodium nitroprusside (P < 0.01) both caused an increase in FBF. There was no significant difference in vascular responses to acetylcholine (P > 0.05) or sodium nitroprusside (P > 0.05) following K(+)-ATP channel blockade.

CONCLUSIONS

The K(+)-ATP channel does not modulate forearm arteriolar endothelium-dependent responses in healthy volunteers and therefore does not play a role in membrane hyperpolarisation.

Alpha-adrenergic receptors in human blood vessels

The evidence for the presence of postjunctional alpha 1- and alpha 2-adrenoceptor subtypes in human blood vessels is reviewed. Experiments in healthy subjects are described that show that alpha 1- as well as alpha 2-adrenoceptor mediated vasoconstriction contribute to vascular smooth muscle tone and that adrenaline and noradrenaline have similar affinities for each subtype. In addition, evidence is presented for a preferential intrajunctional location of alpha 1-adrenoceptors and a preferential extrajunctional location of alpha 2-adrenoceptors in human blood vessels. It is concluded that at present postjunctional alpha-adrenoceptors in human blood vessels can be classified as alpha 1 and alpha 2. Despite the fact that both subtypes mediate vasoconstriction, these receptors are likely to subserve different physiological functions.