Young South Asian women in the United Kingdom show evidence of blunted endothelium-dependent dilatation: implications for future cardiovascular disease.

INTRODUCTION: Prevalence of cardiovascular disease (CVD) is higher in South Asians than white Europeans. The offspring of hypertensive parents (OH) have greater risk of hypertension than offspring of normotensive parents (ON). We hypothesized that endothelium-dependent dilatation is already blunted in young South Asians, relative to young white European women, particularly in South Asian OH women. METHODS: In young white European ON, South Asian ON and OH women (18-25 years old; 10 per group) who were normotensive, we recorded cutaneous perfusion by laser Doppler fluximetry during reactive hyperaemia and iontophoresis of acetylcholine (ACh), before and after inhibiting NO synthesis (NOS) or/and cyclooxygenase (COX). In these and an additional 135 age-matched South Asian and white European women, physical activity and life-style factors were assessed by questionnaire. RESULTS: ACh-evoked dilatation was blunted in young South Asians, relative to white European women. It was attenuated by NOS or COX inhibition in white European ON; by NOS inhibition only in South Asian ON, but not OH women. After combined NOS and COX inhibition, ACh-evoked dilatations were similar to control ACh responses. Similar findings were made for reactive hyperaemia. Questionnaire data indicated young South Asians have lower physical activity levels, fresh fruit and vegetable intake than white European women, South Asian OH being lower than white European ON, or OH women. CONCLUSION: Endothelium-dependent dilatation is blunted in young South Asians, relative to white European women, especially in South Asian OH in whom NO-dependent and prostaglandin-dependent dilatation is blunted. We suggest improved diet and greater physical activity could be particularly effective in improving endothelium-dependent dilatation and reducing future CVD risk in young South Asian OH women.

Resting cardiac sympathetic firing frequencies suppress terminal norepinephrine transporter uptake.

The prejunctional norepinephrine transporter (NET) is responsible for the clearance of released norepinephrine (NE) back into the sympathetic nerve terminal. NET regulation must be tightly controlled as variations could have important implications for neurotransmission. Thus far, the effects of sympathetic neuronal activity on NET function have been unclear. Here, we optically monitor single-terminal cardiac NET activity ex vivo in response to a broad range of sympathetic postganglionic action potential (AP) firing frequencies. Isolated murine left atrial appendages were loaded with a fluorescent NET substrate [Neurotransmitter Transporter Uptake Assay (NTUA)] and imaged with confocal microscopy. Sympathetic APs were induced with electrical field stimulation at 0.2-10 Hz (0.1-0.2 ms pulse width). Exogenous NE was applied during the NTUA uptake- and washout phases to investigate substrate competition and displacement, respectively, on transport. Single-terminal NET reuptake rate was rapidly suppressed in a frequency-dependent manner with an inhibitory EF50 of 0.9 Hz. At 2 Hz, the effect was reversed by the α2-adrenoceptor antagonist yohimbine (1 µM) (p < 0.01) with no further effect imposed by the muscarinic receptor antagonist atropine (1 µM). Additionally, high exogenous NE concentrations abolished NET reuptake (1 µM NE; p < 0.0001) and displaced terminal specific NTUA during washout (1-100 µM NE; p < 0.0001). We have also identified α2-adrenoceptor-induced suppression of NET reuptake rate during resting stimulation frequencies, which could oppose the effect of autoinhibition-mediated suppression of exocytosis and thus amplify the effects of sympathetic drive on cardiac function.

Prostaglandin contribution to postexercise hyperemia is dependent on tissue oxygenation during rhythmic and isometric contractions.

The role of prostaglandins (PGs) in exercise hyperemia is controversial. We tested their contributions in moderate intensity forearm exercise, whether their release is oxygen (O2 )-dependent or affected by aging. A total of 12 young (21 ± 1 years) and 11 older (66 ± 2 years) recreationally active men performed rhythmic and isometric handgrip contractions at 60% maximum voluntary contraction for 3 min during air breathing after placebo, after cyclooxygenase (COX) inhibition with aspirin, while breathing 40% O2 and during their combination (aspirin + 40% O2 ). Forearm blood flow (FBF) was recorded with venous occlusion plethysmography (forearm vascular conductance (FVC): FBF/mean arterial pressure). Venous efflux of PGI2 and PGE2 were assessed by immunoassay. Postcontraction increases in FVC were similar for rhythmic and isometric contractions in young and older men, and accompanied by similar increases in efflux of PGI2 and PGE2 . Aspirin attenuated the efflux of PGI2 by 75%-85%, PGE2 by 50%-70%, (p < .05 within group; p > .05 young versus. older), and postcontraction increases in FVC by 22%-27% and 17%-21% in young and older men, respectively (p < .05 within group and young versus. older). In both age groups, 40% O2 and aspirin + 40% O2 caused similar inhibition of the increases in FVC and efflux of PGs as aspirin alone (p < .05 within group). These results indicate that PGs make substantial contributions to the postcontraction hyperemia of rhythmic and isometric contractions at moderate intensities in recreationally active young and older men. Given PGI2 is mainly released by endothelium and PGE2 by muscle fibers, we propose PG generation is dependent on the contraction-induced falls in O2 at these sites.

Dynamic monitoring of single-terminal norepinephrine transporter rate in the rodent cardiovascular system: A novel fluorescence imaging method.

Here, we validate the use of a novel fluorescent norepinephrine transporter (NET) substrate for dynamic measurements of transporter function in rodent cardiovascular tissue; this technique avoids the use of radiotracers and provides single-terminal resolution. Rodent (Wistar rats and C57BL/6 mice) hearts and mesenteric arteries (MA) were isolated, loaded with NET substrate Neurotransmitter Transporter Uptake Assay (NTUA) ex vivo and imaged with confocal microscopy. NTUA labelled noradrenergic nerve terminals in all four chambers of the heart and on the surface of MA. In all tissues, a temperature-dependent, stable linear increase in intra-terminal fluorescence upon NTUA exposure was observed; this was abolished by NET inhibitor desipramine (1 µM) and reversed by indirectly-acting sympathomimetic amine tyramine (10 µM). NET reuptake rates were similar across the mouse cardiac chambers. In both species, cardiac NET activity was significantly greater than in MA (by 62 ± 29% (mouse) and 21 ± 16% (rat)). We also show that mouse NET reuptake rate was twice as fast as that in the rat (for example, in the heart, by 94 ± 30%). Finally, NET reuptake rate in the mouse heart was attenuated with muscarinic agonist carbachol (10 µM) thus demonstrating the potential for parasympathetic regulation of norepinephrine clearance. Our data provide the first demonstration of monitoring intra-terminal NET function in rodent cardiovascular tissue. This straightforward method allows dynamic measurements of transporter rate in response to varying physiological conditions and drug treatments; this offers the potential to study new mechanisms of sympathetic dysfunction associated with cardiovascular disease.

Contribution of prostaglandins to exercise hyperaemia: workload, ethnicity and sex matter!

The contribution of prostaglandins (PGs) to exercise hyperaemia is controversial. In this review, we argue this is partly explained by differences in exercise intensity between studies. The effects of cyclooxygenase (COX) inhibition and PG assays indicate that PGs contribute more at moderate to heavy than at light workloads and are mainly released by low tissue O2 . But, the release and actions of PGs also depend on other O2 -dependent dilators including ATP, adenosine and NO. K+ may inhibit the action of PGs and other mediators by causing hyperpolarization, but contributes to the hyperaemia. Thus, at lighter loads, the influence of PGs may be blunted by K+ , while COX inhibition leads to compensatory increases in other O2 -dependent dilators. In addition, we show that other sources of variability are sex and ethnicity. Our findings indicate that exercise hyperaemia following rhythmic contractions at 60% maximum voluntary contraction, is smaller in young black African (BA) men and women than in their white European (WE) counterparts, but larger in men than in women of both ethnicities. We propose the larger absolute force in men causes greater vascular occlusion and accumulation of dilators, while blunted hyperaemia in BAs may reflect lower oxidative capacity and O2 requirement. Nevertheless, COX inhibition attenuated peak hyperaemia by ∼30% in WE, BA men and WE women, indicating PGs make a substantial contribution in all three groups. There was no effect in BA women. Lack of PG involvement may provide early evidence of endothelial dysfunction, consistent in BA women with their greater risk of cardiovascular disease.

Cuff inflation time significantly affects blood flow recorded with venous occlusion plethysmography.

PURPOSE: We tested whether the values of limb blood flow calculated with strain-gauge venous occlusion plethysmography (VOP) differ when venous occlusion is achieved by automated, or manual inflation, so providing rapid and slower inflation, respectively. METHOD: In 9 subjects (20-30 years), we calculated forearm blood flows (FBF) values at rest and following isometric handgrip at 70% maximum voluntary contraction (MVC) when rapid, or slower inflation was used. RESULT: Rapid and slower cuff inflation took 0.23 ± 0.01 (mean ± SEM) and 0.92 ± 0.02 s, respectively, reflecting the range reported in published studies. At rest, FBF calculated from the 1st cardiac cycle after rapid and slower inflation gave similar values: 10.5 ± 1.4 vs. 9.6 ± 1.3 ml dl- 1 min- 1, respectively (P > 0.05). However, immediately post-contraction, FBF was ~ 40% lower with slower inflation: 54.6 ± 5.1 vs. 33.8 ± 4.2 ml dl- 1 min- 1 (P < 0.01). The latter value was similar to that calculated over the 3rd cardiac cycle following rapid inflation: 2nd cardiac cycle: 40.5 ± 4.5; 3rd cycle: 32.6 ± 4.5 ml dl- 1 min- 1. Regression analyses of FBFs recorded at intervals post-contraction showed those calculated over the 1st, 2nd, or 3rd cardiac cycles with rapid inflation correlated well with those from the 1st cardiac cycle with manual inflation (r = 0.79, 0.82, 0.79; P < 0.01). However, only the slope for the 3rd cycle with rapid inflation vs. slower inflation was close to unity (2.07, 1.34, and 0.94, respectively). CONCLUSION: These findings confirm that the 1st cardiac cycle following venous occlusion should be used when calculating FBF using VOP and, but importantly, indicate that cuff inflation should be almost instantaneous; just ≥ 0.9 s leads to substantial underestimation, especially at high flows.

Endothelium-dependent and cyclooxygenase-dependent cutaneous vasodilatation is blunted in young men with hypertensive parents.

BACKGROUND: Across ethnicities, offspring of hypertensive parents (OH) have higher risk of hypertension than offspring of normotensive parents (ON). Sympathetic hyperactivity and reduced nitric oxide availability have been reported in normotensive OH; but the role of vasodilator cyclooxygenase (COX) products is unclear. METHODS: In 12 OH and 12 ON men (19-24 years old), each group comprising six white Europeans and six South Asians with resting ABP less than 129/89 mmHg, reactive hyperaemia and responses evoked by iontophoresis pulses of acetylcholine (ACh) were recorded in forearm skin by laser Doppler fluximetry before and after COX inhibition. RESULTS: Peak reactive hyperaemia was larger in ON than OH (71.0 ±â€Š7.8 vs. 43.4 ±â€Š8.3 perfusion units (perf.units); P < 0.05). It was attenuated by COX inhibition in ON (24.8 ±â€Š5.2 perf.units, P < 0.01), not OH (54.2 ±â€Š7.5 perf.units). Similarly, increases in perfusion evoked by ACh were greater in ON than OH (169.1 ±â€Š20.4 vs. 142.1 ±â€Š19.9 perf.units; P < 0.05) and attenuated by COX inhibition in ON (94.5 ±â€Š13.7; P < 0.05), not OH (132.6 ±â€Š16.1 perf.units). Considering ethnicities, ACh-evoked dilation, though not reactive hyperaemia was greater in Europeans than Asians (176.8 ±â€Š21.7 vs. 130.4 ±â€Š15.0; P < 0.01; 61.0 ±â€Š8.7 vs. 51.7 ±â€Š9.2 perf.units). However, within both Europeans and Asians, COX inhibition attenuated reactive hyperaemia and ACh-induced dilatation in ON only. CONCLUSION: Reactive hyperaemia and ACh-evoked dilatation in cutaneous circulation are blunted in young, normotensive OH relative to ON men irrespective of white European, or South Asian ethnicity and are attributable to impaired contribution of COX vasodilator products in OH. These features may provide early markers of endothelial dysfunction that contribute to hypertensive risk in OH men.

Forearm vasodilator responses to environmental stress and reactive hyperaemia are impaired in young South Asian men.

PURPOSE: Prevalence of cardiovascular disease (CVD) is greater in South Asians (SAs) than White Europeans (WEs). Endothelial dysfunction and blunted forearm vasodilatation to environmental stressors have been implicated in CVD. We investigated whether these features are present in young SA men. METHODS: In 15 SA and 16 WE men (19-23 years), we compared changes in forearm blood flow, arterial blood pressure (ABP), forearm vascular conductance (FVC), heart rate, and electrodermal resistance (EDR; sweating) following release of arterial occlusion (reactive hyperaemia endothelium-dependent) and 5 single sounds at 5-10 min intervals (stressors). RESULTS: All were normotensive. Peak reactive hyperaemia was smaller in SAs than WEs (FVC increase: 0.36 ± 0.038 vs 0.44 ± 0.038 units; P < 0.05). Furthermore, in WEs, mean FVC increased at 5, 15, and 20 s of each sound (vasodilatation), but increased at 5 s only in SAs, decreasing by 20 s (vasoconstriction). This reflected a smaller proportion of SAs showing forearm vasodilatation at 15 s (5/15 SAs vs 11/16 WEs: P < 0.01), the remainder showing vasoconstriction. Concomitantly, WEs showed greater bradycardia and EDR changes. Intra-class correlation analyses showed that all responses were highly reproducible over five sounds in both WEs and SAs. Moreover, sound-evoked changes in ABP and FVC were negatively correlated in each ethnicity (P < 0.01). However, WEs showed preponderance of forearm vasodilatation and depressor responses; SAs showed preponderance of vasoconstriction and pressor responses. CONCLUSIONS: Endothelium-dependent vasodilatation is blunted in young SA men. This could explain their impaired forearm vasodilatation and greater pressor responses to repeated environmental stressors, so predisposing SAs to hypertension and CVD.

Development of microdialysis methodology for interstitial insulin measurement in rodents.

INTRODUCTION: Accurate assessment of muscle insulin sensitivity requires measurement of insulin concentration in interstitial fluid (ISF), but has proved difficult. We aimed to optimise measurement of ISF insulin concentrations in rat muscles in vivo using microdialysis. METHODS: Factorial experimental design experiments were performed in vitro to determine optimal conditions for insulin recovery with microdialysis probes. These conditions were tested in vivo, adjusted appropriately and used in lean and obese Zucker rats to compare ISF insulin concentrations basally and during hyperinsulinaemic-euglycaemic (HE) clamp. RESULTS: Optimal conditions in vivo were: a 100kDa microdialysis probe inserted in muscle, perfused with 1% BSA, 1.5mM glucose in 0.9% sodium chloride at 1µl/min. Samples were collected into siliconised glass microvials. As a reference for insulin, we established a protocol of inulin infusion, beginning at -80min and reaching equilibrium within 60min. HE clamp, beginning at 0min, increased ISF insulin concentration from 122±56 basally to 429±180pmol/l (P<0.05) in lean rats and from 643±165 to 1087±243pmol/l (P=0.07) in obese rats; ISF insulin concentrations were significantly higher throughout in obese rats. The difference between ISF and plasma insulin concentration (ISF:plasma ratio) was substantially higher in obese rats, but fell to similar values in obese and lean rats during HE clamp. DISCUSSION: Optimising insulin recovery with microdialysis allowed accurate measurement of basal ISF insulin in muscle of lean and obese Zucker rats and indicates insulin transport across capillaries is impaired in obese rats, basally and during hyperinsulinaemia.

Interactions between local dilator and sympathetic vasoconstrictor influences in skeletal muscle in acute and chronic hypoxia.

NEW FINDINGS: What is the topic of this review? This review considers how local dilator mechanisms and increased sympathetic nerve activity interact during acute systemic hypoxia and then reviews current understanding of some of the modifications induced by chronic hypoxia. What advances does it highlight? During acute hypoxia, local levels of hypoxia determine the release of vasodilators and magnitude of arteriolar dilatation, as well as the extent to which sympathetically evoked vasoconstriction is blunted, so maximizing distribution of O2 to muscle fibres. Chronic hypoxia in adult life and fetal programming induced by chronic hypoxia in utero lead to increased responsiveness to acute hypoxia and further blunting of sympathetic vasoconstriction, but are also associated with hypertension. In resting skeletal muscle, acute systemic hypoxia evokes vasodilatation, while vasoconstriction evoked by increased muscle sympathetic nerve activity is blunted, referred to herein as hypoxic sympatholysis. This review considers the contributions of adenosine, prostaglandin I2 , nitric oxide, ATP and endothelium-derived hyperpolarizing factors to the muscle vasodilatation, with particular attention being given to the release and actions of adenosine, which plays a dominant role. It is argued that the dilator substances are released in proportion to the local level of hypoxia, notably, allowing terminal arterioles to regulate O2 distribution through the capillaries. Correspondingly, hypoxic sympatholysis can be attributed to the ability of local hypoxia to blunt vasoconstriction evoked by noradrenaline acting on α1 - and α2 -adrenoceptors. The synergistic actions of ATP as cotransmitter may be depressed in parallel, but the actions of neuropeptide Y persist. Consideration is also given to the changes induced by chronic hypoxia in adult life and to the consequences in adult life of fetal programming induced by chronic hypoxia during pregnancy. In both conditions, dilator responsiveness to acute hypoxia is maintained, but the action or release of adenosine is altered in ways that are not yet understood. Both conditions are also accompanied by blunted sympathetically evoked vasoconstriction, tonically raised muscle sympathetic nerve activity, and increased muscular vascular tone and arterial blood pressure. With hypoxia-induced fetal programming, arterial pressure is increased in young adults and increases with age. The mechanisms underlying these changes are discussed, and it is argued that chronic hypoxia in adult life or in utero may facilitate development of hypertension.

Effects of modest hyperoxia and oral vitamin C on exercise hyperaemia and reactive hyperaemia in healthy young men.

PURPOSE: We have argued that breathing 40 % O2 attenuates exercise hyperaemia by decreasing production of O2-dependent vasodilators. However, breathing 100 % O2 attenuated endothelium-dependent vasodilatation evoked by acetylcholine and this effect was prevented by vitamin C, implicating reactive oxygen species (ROS). We have therefore used vitamin C to test the hypothesis that 40 % O2 modulates exercise hyperaemia and reactive hyperaemia independently of ROS. METHOD: In a cross-over study on 10 male subjects (21.1 ± 0.84 years), we measured forearm blood flow (venous occlusion plethysmography) and calculated forearm vascular conductance (FVC) at rest and following static handgrip at 60 % maximum voluntary contraction for 2 min and following arterial occlusion for 2 min, after placebo or oral vitamin C (2000 mg), and when breathing air or 40 % O2. RESULT: During air breathing, vitamin C augmented the peak increase in FVC following static contraction, or release of arterial occlusion, by ~50 or 60 %, respectively (P < 0.05). Breathing 40 % O2 in the presence of placebo attenuated post-contraction hyperaemia by ~25 % (P < 0.05), but had no effect on reactive hyperaemia. By contrast, in the presence of vitamin C, 40 % O2 attenuated the peak increase in FVC following static contraction, or release of arterial occlusion by ~25 and 50 %, respectively (P < 0.05). CONCLUSION: These results indicate that in young men, exercise hyperaemia following strenuous muscle contraction and reactive hyperaemia are blunted by ROS. However, they are also consistent with the view that modest hyperoxia induced by breathing 40 % O2 acts independently of ROS to attenuate not only post-contraction hyperaemia, but also reactive hyperaemia, by decreasing release of O2-dependent vasodilators.

Prenatal hypoxia leads to increased muscle sympathetic nerve activity, sympathetic hyperinnervation, premature blunting of neuropeptide Y signaling, and hypertension in adult life.

Adverse conditions prenatally increase the risk of cardiovascular disease, including hypertension. Chronic hypoxia in utero (CHU) causes endothelial dysfunction, but whether sympathetic vasoconstrictor nerve functioning is altered is unknown. We, therefore, compared in male CHU and control (N) rats muscle sympathetic nerve activity, vascular sympathetic innervation density, and mechanisms of sympathetic vasoconstriction. In young (Y)-CHU and Y-N rats (≈3 months), baseline arterial blood pressure was similar. However, tonic muscle sympathetic nerve activity recorded focally from arterial vessels of spinotrapezius muscle had higher mean frequency in Y-CHU than in Y-N rats (0.56±0.075 versus 0.33±0.036 Hz), and the proportions of single units with high instantaneous frequencies (1-5 and 6-10 Hz) being greater in Y-CHU rats. Sympathetic innervation density of tibial arteries was ≈50% greater in Y-CHU than in Y-N rats. Increases in femoral vascular resistance evoked by sympathetic stimulation at low frequency (2 Hz for 2 minutes) and bursts at 20 Hz were substantially smaller in Y-CHU than in Y-N rats. In Y-N only, the neuropeptide Y Y1-receptor antagonist BIBP3226 attenuated these responses. By contrast, baseline arterial blood pressure was higher in middle-aged (M)-CHU than in M-N rats (≈9 months; 139±3 versus 126±3 mm Hg, respectively). BIBP3226 had no effect on femoral vascular resistance increases evoked by 2 Hz or 20 Hz bursts in M-N or M-CHU rats. These results indicate that fetal programming induced by prenatal hypoxia causes an increase in centrally generated muscle sympathetic nerve activity in youth and hypertension by middle age. This is associated with blunting of sympathetically evoked vasoconstriction and its neuropeptide Y component that may reflect premature vascular aging and contribute to increased risk of cardiovascular disease.

Contribution of non-endothelium-dependent substances to exercise hyperaemia: are they O(2) dependent?

This review considers the contributions to exercise hyperaemia of substances released into the interstitial fluid, with emphasis on whether they are endothelium dependent or O(2) dependent. The early phase of exercise hyperaemia is attributable to K(+) released from contracting muscle fibres and acting extraluminally on arterioles. Hyperpolarization of vascular smooth muscle and endothelial cells induced by K(+) may also facilitate the maintained phase, for example by facilitating conduction of dilator signals upstream. ATP is released into the interstitium from muscle fibres, at least in part through cystic fibrosis transmembrane conductance regulator-associated channels, following the fall in intracellular H(+). ATP is metabolized by ectonucleotidases to adenosine, which dilates arterioles via A(2A) receptors, in a nitric oxide-independent manner. Evidence is presented that the rise in arterial achieved by breathing 40% O(2) attenuates efflux of H(+) and lactate, thereby decreasing the contribution that adenosine makes to exercise hyperaemia; efflux of inorganic phosphate and its contribution may likewise be attenuated. Prostaglandins (PGs), PGE(2) and PGI(2), also accumulate in the interstitium during exercise, and breathing 40% O(2) abolished the contribution of PGs to exercise hyperaemia. This suggests that PGE(2) released from muscle fibres and PGI(2) released from capillaries and venular endothelium by a fall in their local act extraluminally to dilate arterioles. Although modest hyperoxia attenuates exercise hyperaemia by improving O(2) supply, limiting the release of O(2)-dependent adenosine and PGs, higher O(2) concentrations may have adverse effects. Evidence is presented that breathing 100% O(2) limits exercise hyperaemia by generating O(2)(-), which inactivates nitric oxide and decreases PG synthesis.

Breathing 40% O(2) can attenuate postcontraction hyperaemia or muscle fatigue caused by static forearm contraction, depending on timing.

Little is known of the role of O(2)-dependent mechanisms in the hyperaemia associated with static muscle contraction or recovery from fatigue. Thus, in recreationally active, young, male subjects, forearm contraction was performed twice at 100% maximal voluntary effort until exhaustion, with a 7 min recovery period, whilst 40% O(2) (hyperoxia) was breathed during the contractions only, or during recovery only, or room air (normoxia) was breathed throughout. When hyperoxia was limited to the contractions, postcontraction increases in forearm blood flow, measured by venous occlusion plethysmography, were ∼25% lower (P < 0.05, n = 10) than during normoxia throughout. Furthermore, the postcontraction increase in venous lactate and fall in pH were attenuated (P < 0.05, n = 8). However, there was no effect on fatigue; time to voluntary exhaustion of contraction 2 was ∼25% less than for contraction 1 in both conditions. By contrast, when hyperoxia was limited to recovery (n = 10), there was no effect on postcontraction increases in forearm blood flow, but fatigue was ameliorated; time to voluntary exhaustion of contraction 2 was comparable to that of contraction 1. These results allow the novel conclusions that, even during static forearm contraction at 100% maximal voluntary effort, additional O(2) dissolved in plasma can attenuate the contribution made by O(2)-dependent dilator substances to postcontraction hyperaemia and that these substances may be released from the muscle fibres or blood vessel wall. Furthermore, they indicate that even in recreationally active individuals, recovery from fatigue can be improved by additional O(2) made available during recovery, and the O(2)-dependent mechanisms that contribute to fatigue are different from those that induce postcontraction hyperaemia.

Effects of cyclooxygenase inhibition on vascular responses evoked in fingers of men and women by iontophoresis of 1- and 2-adrenoceptor agonists.

In 10 men and nine women aged 20-23 years, we aimed to establish whether endogenous prostanoids synthesised by cyclooxygenase (COX) affect responses evoked in the finger by α(1)- or α(2)-adrenoceptor agonists. Cutaneous red cell flux (cRCF) was recorded in dorsal finger during iontophoresis of phenylephrine (PE) or clonidine (0.5 mm, seven 0.1 mA pulses followed by one 0.2 mA pulse: 30 s each at 60 s intervals) before and after the COX inhibitor aspirin (600 mg p.o.). In men, PE evoked a biphasic mean increase/decrease in cRCF before but a monophasic mean decrease in cRCF of 30-40% after aspirin (P < 0.05). In women in the low oestrogen (E(2)) phase of the menstrual cycle, PE evoked a decrease in cRCF (30-40%; P < 0.05) that was unchanged by aspirin, whereas in the high E(2) phase, PE evoked no change before but a graded decrease in cRCF (30-40%; P < 0.05) after aspirin. Clonidine evoked a decrease in cRCF (∼30%; P < 0.05) in men before, but not after, aspirin. Clonidine evoked both increases and decreases in cRCF before and after aspirin in women in the low and high E(2) phases (P > 0.05). We propose that finger vasoconstriction evoked by extraluminal α(1)-adrenoceptor stimulation is blunted by vasodilator COX products in young men and overcome by their action in women in the high, but not low E(2), phase of the menstrual cycle. By contrast, α(2)-adrenoceptor stimulation evokes finger vasoconstriction that is mediated by vasoconstrictor COX products in young men, but evokes no consistent response in women in the low or high E(2) phases of the menstrual cycle.

Changes in muscle sympathetic nerve activity and vascular responses evoked in the spinotrapezius muscle of the rat by systemic hypoxia.

Responses evoked in muscle sympathetic nerve activity (MSNA) by systemic hypoxia have received relatively little attention. Moreover, MSNA is generally identified from firing characteristics in fibres supplying whole limbs: their actual destination is not determined. We aimed to address these limitations by using a novel preparation of spinotrapezius muscle in anaesthetised rats. By using focal recording electrodes, multi-unit and discriminated single unit activity were recorded from the surface of arterial vessels.This had cardiac- and respiratory-related activities expected of MSNA, and was increased by baroreceptor unloading, decreased by baroreceptor stimulation and abolished by autonomic ganglion blockade. Progressive, graded hypoxia (breathing sequentially 12, 10, 8% O2 for 2min each) evoked graded increases in MSNA.In single units, mean firing frequency increased from 0.2±0.04 in 21% O2 to 0.62 ± 0.14 Hz in8% O2, while instantaneous frequencies ranged from 0.04­6Hz in 21% O2 to 0.09­20 Hz in 8%O2. Concomitantly, arterial pressure (ABP), fell and heart rate (HR) and respiratory frequency(RF) increased progressively, while spinotrapezius vascular resistance (SVR) decreased (Spinotrapezius blood flow/ABP), indicating muscle vasodilatation. During 8% O2 for 10 min, the falls in ABP and SVR were maintained, but RF, HR and MSNA waned towards baselines from the second to the tenth minute. Thus, we directly show that MSNA increases during systemic hypoxia to an extent that is mainly determined by the increases in peripheral chemoreceptor stimulation and respiratory drive, but its vasoconstrictor effects on muscle vasculature are largely blunted by local dilator influences, despite high instantaneous frequencies in single fibres.

Endothelium-dependent and endothelium-independent vasodilatation of the cutaneous circulation in sickle cell disease.

BACKGROUND: Whilst there is evidence of endothelial dysfunction in sickle cell disease (SCD), whether this affects regulation in the microcirculation is not known. METHODS: We studied 19 patients with SCD, eight with sickle cell-haemoglobin C (HbSC), 11 with homozygous sickle cell (HbSS) disease and 11 matched control subjects with normal haemoglobin genotype (HbAA). Vasodilator responses were evoked by iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) in finger and forearm, cutaneous red cell flux (RCF) being measured by laser Doppler fluximetry. RESULTS: Increases in RCF evoked in the finger by ACh were not different between SCD and HbAA subjects (P = 0·789), but were smaller in patients with HbSS than HbSC (P < 0·05). By contrast, increases in RCF evoked in forearm by ACh were greater in SCD than HbAA subjects (P < 0·05) and similar in patients with HbSC and HbSS. Increases in RCF evoked by SNP did not differ between patients with SCD and HbAA subjects in finger or forearm. CONCLUSIONS: Our results indicate that endothelium-dependent cutaneous vasodilatation is augmented in forearm of patients with SCD relative to HbAA subjects, but impaired in the finger of SCD patients with the more severe HbSS genotype. Thus, endothelial dysfunction associated with SCD is not accompanied by generalised impairment in endothelium-dependent dilatation, but with more localised impairment that includes the fingers of patients with HbSS.

Effects of maternal hypoxia on muscle vasodilatation evoked by acute systemic hypoxia in adult rat offspring: changed roles of adenosine and A1 receptors.

Suboptimal conditions in utero can have long-lasting effects including increased risk of cardiovascular disease in adult life. Such programming effects may be induced by chronic systemic hypoxia in utero (CHU). We have investigated how CHU affects cardiovascular responses evoked by acute systemic hypoxia in adult male offspring, recognising that adenosine contributes to hypoxia-induced muscle vasodilatation and bradycardia by acting on A(1) receptors in normal (N) rats. In the present study, dams were housed in a hypoxic chamber at 12% O(2) for the second half of gestation; offspring were born and reared in air until 9-10 weeks of age. Under anaesthesia, acute systemic hypoxia (breathing 8% O(2) for 5 min) evoked similar biphasic tachycardia/bradycardia, fall in arterial pressure and increase in femoral vascular conductance (FVC) in N and CHU rats (+2.0 vs. +2.7 conductance units respectively). However, in CHU rats, neither the non-selective adenosine receptor antagonist 8-sulphophenyltheopylline (8-SPT), nor the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) affected the increase in FVC, but DPCPX attenuated the hypoxia-induced bradycardia. Further, in N and CHU rats, 5 min infusion of adenosine induced similar increases in FVC; in CHU rats, DPCPX reduced the adenosine-induced increase in FVC (by >50%) and accentuated the concomitant tachycardia. These results suggest that CHU rats have functional A(1) receptors in heart and vasculature, but the release and/or vasodilator influence of adenosine on the endothelium in acute hypoxia is attenuated and replaced by other dilator factors. Such changes from normal endothelial function may have implications for general cardiovascular regulation.