H1 and H2 receptors mediate postexercise hyperemia in sedentary and endurance exercise-trained men and women

Effect of H1- and H2-histamine receptor blockade on postexercise insulin sensitivity

Following a bout of dynamic exercise, humans experience sustained postexercise vasodilatation in the previously exercised skeletal muscle which is mediated by activation of histamine (H1 and H2) receptors. Skeletal muscle glucose uptake is also enhanced following dynamic exercise. Our aim was to determine if blunting the vasodilatation during recovery from exercise would have an adverse effect on blood glucose regulation. Thus, we tested the hypothesis that insulin sensitivity following exercise would be reduced with H1- and H2-receptor blockade versus control (no blockade). We studied 20 healthy young subjects (12 exercise; eight nonexercise sham) on randomized control and H1- and H2-receptor blockade (fexofenadine and ranitidine) days. Following 60 min of upright cycling at 60% VO2 peak or nonexercise sham, subjects consumed an oral glucose tolerance beverage (1.0 g/kg). Blood glucose was determined from "arterialized" blood samples (heated hand vein). Postexercise whole-body insulin sensitivity (Matsuda insulin sensitivity index) was reduced 25% with H1- and H2-receptor blockade (P < 0.05), whereas insulin sensitivity was not affected by histamine receptor blockade in the sham trials. These results indicate that insulin sensitivity following exercise is blunted by H1- and H2-receptor blockade and suggest that postexercise H1- and H2-receptor-mediated skeletal muscle vasodilatation benefits glucose regulation in healthy humans.

Haemodynamic responses to dehydration in the resting and exercising human leg

Dehydration and hyperthermia reduces leg blood flow (LBF), cardiac output ([Formula: see text]) and arterial pressure during whole-body exercise. It is unknown whether the reductions in blood flow are associated with dehydration-induced alterations in arterial blood oxygen content (C aO2) and O2-dependent signalling. This study investigated the impact of dehydration and concomitant alterations in C aO2 upon LBF and [Formula: see text]. Haemodynamics, arterial and femoral venous blood parameters and plasma [ATP] were measured at rest and during one-legged knee-extensor exercise in 7 males in four conditions: (1) control, (2) mild dehydration, (3) moderate dehydration, and (4) rehydration. Relative to control, C aO2 and LBF increased with dehydration at rest and during exercise (C aO2: from 199 ± 1 to 208 ± 2, and 202 ± 2 to 210 ± 2 ml L(-1) and LBF: from 0.38 ± 0.04 to 0.77 ± 0.09, and 1.64 ± 0.09 to 1.88 ± 0.1 L min(-1), respectively). Similarly, [Formula: see text] was unchanged or increased with dehydration at rest and during exercise, whereas arterial and leg perfusion pressures declined. Following rehydration, C aO2 declined (to 193 ± 2 mL L(-1)) but LBF remained elevated. Alterations in LBF were unrelated to C aO2 (r (2) = 0.13-0.27, P = 0.48-0.64) and plasma [ATP]. These findings suggest dehydration and concomitant alterations in C aO2 do not compromise LBF despite reductions in plasma [ATP]. While an additive or synergistic effect cannot be excluded, reductions in LBF during exercise with dehydration may not necessarily be associated with alterations in C aO2 and/or intravascular [ATP].

Free radical-mediated lipid peroxidation and systemic nitric oxide bioavailability: implications for postexercise hemodynamics

BACKGROUND

The metabolic vasodilator mediating postexercise hypotension (PEH) is poorly understood. Recent evidence suggests an exercise-induced reliance on pro-oxidant-stimulated vasodilation in normotensive young human subjects, but the role in the prehypertensive state is not known.

METHODS

Nine prehypertensives (mean arterial pressure (MAP), 106 ± 5 mm Hg; 50 ± 10 years old) performed 30 minutes of cycle exercise and a nonexercise trial. Arterial distensibility was characterized by simultaneously recording upper- and lower-limb pulse wave velocity (PWV) via oscillometry. Systemic vascular resistance and conductance were determined by MAP/Q and Q/MAP, respectively. Venous blood was assayed for indirect markers of oxidative stress (lipid hydroperoxides (LOOH); spectrophotometry), plasma nitric oxide (NO) and S-nitrosothiols (fluorometry), atrial natriuretic peptide (ANP), and angiotensin II (ANG-II) (radioimmunoassay).

RESULTS

Exercise reduced MAP (6mm Hg) and vascular resistance (15%) at 60 minutes after exercise, whereas conductance was elevated (20%) (P < 0.05). The hypotension resulted in a lower MAP at 60 and 120 minutes after exercise compared with nonexercise (P < 0.05). Upper-limb PWV was also 18% lower after exercise compared with baseline (P < 0.05). Exercise increased LOOH coincident with the nadir in hypotension and vascular resistance but failed to affect plasma NO or S-nitrosothiols. Exercise-induced increases in LOOH were related to ANG-II (r = 0.97; P < 0.01) and complemented by elevated ANP concentrations.

CONCLUSIONS

These data indicate attenuated vascular resistance after exercise with increased oxidative stress and unchanged NO. Whether free radicals are obligatory for PEH requires further investigation, although it seems that oxidative stress occurs during the hyperemia underlying PEH.

Postexercise hypotension and sustained postexercise vasodilatation: what happens after we exercise?

A single bout of aerobic exercise produces a postexercise hypotension associated with a sustained postexercise vasodilatation of the previously exercised muscle. Work over the last few years has determined key pathways for the obligatory components of postexercise hypotension and sustained postexercise vasodilatation and points the way to possible benefits that may result from these robust responses. During the exercise recovery period, the combination of centrally mediated decreases in sympathetic nerve activity with a reduced signal transduction from sympathetic nerve activation into vasoconstriction, as well as local vasodilator mechanisms, contributes to the fall in arterial blood pressure seen after exercise. Important findings from recent studies include the recognition that skeletal muscle afferents may play a primary role in postexercise resetting of the baroreflex via discrete receptor changes within the nucleus tractus solitarii and that sustained postexercise vasodilatation of the previously active skeletal muscle is primarily the result of histamine H(1) and H(2) receptor activation. Future research directions include further exploration of the potential benefits of these changes in the longer term adaptations associated with exercise training, as well as investigation of how the recovery from exercise may provide windows of opportunity for targeted interventions in patients with hypertension and diabetes.

Sustained postexercise vasodilatation and histamine receptor activation following small muscle-mass exercise in humans

A sustained postexercise vasodilatation, which is histamine receptor mediated, has been observed following single bouts of whole-body exercise, but the mechanisms that regulate activation of histamine receptors following exercise are undefined. Exploration of vasodilatation after small muscle-mass dynamic or resistance exercise could provide novel insight into the pathways responsible for histamine receptor activation. We hypothesized that there would be a vasodilatation of the previously exercised limb following small muscle-mass dynamic and resistance exercise, which would be mediated by histamine receptors. We studied men and women before and after single-leg dynamic (n = 9) or resistance knee-extension exercise (n = 12) on control and blockade days (combined oral H(1) and H(2) receptor antagonism with fexofenadine and ranitidine). We measured arterial blood pressure (automated brachial oscillometry) and femoral artery blood flow (Doppler ultrasound). Dynamic exercise elevated leg vascular conductance in the active leg by 27.2 ± 8.4% at 60 min postexercise (P < 0.05 versus pre-exercise), but did not alter conductance in the rested leg (change, 4.6 ± 3.5%; P = 0.8 versus pre-exercise). The rise in conductance was abolished on the blockade day (change, 3.7 ± 5.1%; P = 0.8 versus pre-exercise, P = 0.2 versus control). Resistance exercise did not produce a sustained vasodilatation (change, -4.3 ± 4.7% at 60 min postexercise; P = 0.7 versus pre-exercise). These data indicate that histamine receptors are activated following dynamic, but not resistance, exercise. Furthermore, these data suggest that local factors associated with aerobic exercise, and not systemic factors or factors associated with high muscle force, are responsible for activation of histamine receptors in the previously exercised muscle.

Hypotensive response after water-walking and land-walking exercise sessions in healthy trained and untrained women

Background:

The aim of this study was to compare post-exercise hypotension after acute sessions of water-walking and land-walking in healthy trained and untrained women.

Methods:

Twenty-three untrained (n = 12) and trained (n = 11) normotensive women performed two walking sessions in water and on land at 40% of peak VO₂ for 45 minutes. Systolic and diastolic blood pressure and mean arterial pressure were measured 15, 30, 45, and 60 minutes after the exercise sessions.

Results:

No differences were found between the groups for age and anthropometric parameters, but peak VO₂ for the trained women (45 ± 8 mL/kg/minute) was higher than for the untrained women (31 ± 3 mL/kg/minute). No differences were found between the groups with regard to systolic and diastolic blood pressure and mean arterial pressure after water immersion. The heart rate in the trained group (62 ± 3 beats per minute [bpm]) was significantly lower (P < 0.05) than in the untrained group (72 ± 4 bpm) on land, and after water immersion, this difference disappeared (58 ± 5 bpm in the trained women and 66 ± 5 bpm in the untrained women). Sixty minutes after water-walking, systolic blood pressure (108 ± 8 mmHg vs 97 ± 3 mmHg), diastolic blood pressure (69 ± 5 mmHg vs 62 ± 5 mmHg), and mean arterial pressure (82 ± 6 mmHg vs 74 ± 4 mmHg) decreased significantly with rest in the untrained group, and no differences were found after land-walking. In the trained group, significant (P < 0.05) differences were found only for systolic blood pressure (110 ± 9 mmHg vs 100 ± 9 mmHg) after 60 minutes of water-walking; decreases in systolic blood pressure were found after 45 minutes (99 ± 7 mmHg) and 60 minutes (99 ± 6 mmHg) compared with rest (107 ± 5 mmHg) after land-walking.

Conclusion:

Single water-walking and land-walking sessions induced important hypotension following exercise. Additionally, walking performed in chest-deep water has a better effect on exercise-induced hypotension in untrained healthy women than walking at a similar intensity on land.

Local histamine H(1-) and H(2)-receptor blockade reduces postexercise skeletal muscle interstitial glucose concentrations in humans

Elevated blood flow can potentially influence skeletal muscle glucose uptake, but the impact of postexercise hyperemia on glucose availability to skeletal muscle remains unknown. Because postexercise hyperemia is mediated by histamine H(1)- and H(2)-receptors, we tested the hypothesis that postexercise interstitial glucose concentrations would be lower in the presence of combined H1- and H2-receptor blockade. To this end, 4 microdialysis probes were inserted into the vastus lateralis muscle of 14 healthy subjects (21-27 years old) immediately after 60 min of either upright cycling at 60% peak oxygen uptake (exercise, n = 7) or quiet rest (sham, n = 7). Microdialysis probes were perfused with a modified Ringer's solution containing 3 mmol L(-1) glucose, 5 mmol L(-1) ethanol, and [6-3H] glucose (200 disintegrations·min-1 microL(-1)). Two sites (blockade) received both H1- and H2-receptor antagonists (1 mmol L(-1) pyrilamine and 3 mmol L-1 cimetidine) and 2 sites (control) did not receive antagonists. Ethanol outflow/inflow ratios (an inverse surrogate of local blood flow) were higher in blockade sites than in control sites following exercise (p < 0.05), whereas blockade had no effect on ethanol outflow/inflow ratios following sham (p = 0.80). Consistent with our hypothesis, during 3 of the 5 dialysate collection periods, interstitial glucose concentrations were lower in blockade sites vs. control sites following exercise (p < 0.05), whereas blockade had no effect on interstitial glucose concentrations following sham (p = 0.79). These findings indicate that local H1- and H2-receptor activation modulates skeletal muscle interstitial glucose levels during recovery from exercise in humans and suggest that the availability of glucose to skeletal muscle is enhanced by postexercise hyperemia.

Postexercise hypotension in an endurance-trained population of men and women following high-intensity interval and steady-state cycling

BACKGROUND

The acute effect of high-intensity interval exercise (HI) on blood pressure (BP) is unknown although this type of exercise has similar or greater cardiovascular benefits compared to steady-state aerobic exercise (SS). This study examined postexercise hypotension (PEH) and potential mechanisms of this response in endurance-trained subjects following acute SS and HI. Sex differences were also evaluated.

METHODS

A total of 25 endurance-trained men (n = 15) and women (n = 10) performed a bout of HI and a bout of SS cycling in randomized order on separate days. Before exercise, 30 min postexercise, and 60 min postexercise, we measured brachial and aortic BP. Cardiac output (CO), stroke volume (SV), end diastolic volume (EDV), end systolic volume (ESV), and left ventricular wall-velocities were measured using ultrasonography with tissue Doppler capabilities. Ejection fraction and fractional shortening (FS), total peripheral resistance (TPR), and calf vascular resistance were calculated from the above variables and measures of leg blood flow.

RESULTS

BP, ejection fraction, and FS decreased by a similar magnitude following both bouts but changes in CO, heart rate (HR), TPR, and calf vascular resistance were greater in magnitude following HI than following SS. Men and women responded similarly to HI. Although men and women exhibited a similar PEH following SS, they showed differential changes in SV, EDV, and TPR.

CONCLUSIONS

HI acutely reduces BP similarly to SS. The mechanistic response to HI appears to differ from that of SS, and endurance-trained men and women may exhibit differential mechanisms for PEH following SS but not HI.

Blood flow in the brachial artery increases after intense cycling exercise

During cycling blood flow is redistributed from physically inactive tissues to working leg muscles. It is unknown how long this situation persists after very intense exercise or whether it differs between intense exhausting and non-exhausting exercise. It is also not known to what extent the redistribution differs between different types of non-active tissues. Therefore nine healthy young men cycled first for 2 min at 328 W (non-exhausting exercise, mean). Blood velocity in thigh and arm (ultrasound-doppler), perfusion of forearm skin (non-acral skin) and finger tip (acral skin, with arterio-venous anastomoses) were measured for 30 min after exercise (laser-doppler). To be able to study vascular resistance and central circulation, blood pressure (Finometer), heart rate (ECG), and stroke volume (ultrasound-doppler) were measured. Thereafter the subjects cycled at the same power to exhaustion (4 min), and the measurements were repeated. After both exercises mean blood pressure was unchanged (< or = 80 mm Hg) despite increased cardiac output (> or = + 30% vs. pre-exercise). Blood velocity in the brachial artery was higher during the whole recovery period than at rest (p< or =0.02; no differences between exercises). Blood perfusion of non-acral skin was unchanged from pre-exercise level after 2 min of non-exhausting exercise, but it was twice as high after 4 min cycling to exhaustion as at rest (p=0.02). Blood perfusion of acral skin rose after both exercises and did not differ between exhausting and non-exhausting exercise. In conclusion, arm blood flow increases above the pre-exercise level in the recovery period after short-lasting, strenuous exercise.

Fluid replacement and heat stress during exercise alter post-exercise cardiac haemodynamics in endurance exercise-trained men

It has been reported that endurance exercise-trained men have decreases in cardiac output with no change in systemic vascular conductance during post-exercise hypotension, which differs from sedentary and normally active populations. As inadequate hydration may explain these differences, we tested the hypothesis that fluid replacement prevents this post-exercise fall in cardiac output, and further, exercise in a warm environment would cause greater decreases in cardiac output. We studied 14 trained men (VO2,peak 4.66 +/- 0.62 l min(-1)) before and to 90 min after cycling at 60% VO2,peak for 60 min under three conditions: Control (no water was consumed during exercise in a thermoneutral environment), Fluid (water was consumed to match sweat loss during exercise in a thermoneutral environment) and Warm (no water was consumed during exercise in a warm environment). Arterial pressure and cardiac output were measured pre- and post-exercise in a thermoneutral environment. The fall in mean arterial pressure following exercise was not different between conditions (P = 0.453). Higher post-exercise cardiac output (Delta 0.41 +/- 0.17 l min(-1); P = 0.027), systemic vascular conductance (Delta 6.0 +/- 2.2 ml min(-1) mmHg(-1); P = 0.001) and stroke volume (Delta 9.1 +/- 2.1 ml beat(-1); P < 0.001) were seen in Fluid compared to Control, but there was no difference between Fluid and Warm (all P > 0.05). These data suggest that fluid replacement mitigates the post-exercise decrease in cardiac output in endurance-exercise trained men. Surprisingly, exercise in a warm environment also mitigates the post-exercise fall in cardiac output.

Post-exercise hypotension and cardiovascular responses to moderate orthostatic stress in endurance-trained males

We tested the hypothesis that following an acute bout of exercise cardiovascular and cerebrovascular responses to lower-body negative pressure (LBNP) would be altered due to post-exercise hypotension (PEH). Ten healthy, male, endurance-trained athletes (mean age ± SD = 29.6 ± 5) were assessed for cardiovascular and cerebrovascular responses to LBNP following acute bouts of interval and continuous exercise. Mean arterial pressure (MAP), cardiac output, total peripheral resistance, heart rate variability, and total cerebral oxygen index were determined during a baseline LBNP session. These indices were also determined during two other LBNP sessions: following an acute bout of interval exercise, and following an acute bout of continuous exercise. Compared with baseline, MAP was reduced after both exercise conditions, similar to values previously reported (10 mmHg; p < 0.05 vs. pre-exercise). Total peripheral resistance was significantly reduced following both exercise bouts, and heart rate was significantly increased post-exercise (rest: 59.6 ± 11.2; interval: 77.8 ± 12.8; continuous: 80.3 ± 15.2 beats·min–1). Both cardiac output and stroke volume responses to LBNP following exercise were not altered when compared with baseline measurements. Tissue oxygenation during –40 mmHg (interval: 74.31% ± 7.82% vs. continuous: 69.13% ± 5.23%) was significantly lower than during normobaric pressure (interval: 77.14% ± 1.30% vs. continuous: 74.41% ± 0.94%). It appears from these observations that although young, endurance-trained males experience PEH following acute bouts of interval or continuous exercise, this hypotension does not alter the cardiovascular and cerebrovascular responses to a moderate orthostatic stress.

A modern classification of the exercise-related heat illnesses

This article proposes a novel framework classification for the heat illnesses. It argues that heat stroke is the only described condition that is truly a "heat illness" since it is the only condition in which there is clear evidence for a pathological elevation of the core body temperature. If this is correct the non-descript terms such as heat fatigue, heat exhaustion and heat syncopy should be removed from the modern lexicon. Since the evidence is that most cases of post-exercise collapse are due to the development of postural hypotension immediately on the cessation of exercise, it is further proposed that more specific terms such as exercise-associated postural hypotension should be used, when appropriate, to replace the non-descript terms such as heat exhaustion, heat fatigue or heat syncopy. Furthermore this novel classification acknowledges that heat stroke may occur in some as a result of accelerated rates of endogenous heat production (thermogenesis). It also suggests that the elevated body temperature alone may not be the sole cause of fatal outcomes in heat stroke but that toxic chemicals released from damaged muscles by the processes causing this accelerated thermogenesis may also be involved.

Increase in kinins on post-exercise hypotension in normotensive and hypertensive volunteers

Post-exercise hypotension is an important event for blood pressure regulation, especially in hypertensive individuals. Although post-exercise hypotension is a well-known phenomenon, the mechanism responsible is still unclear. The kallikrein-kinin system is involved in blood pressure control, but its role in post-exercise hypotension has not yet been investigated. Thus, the purpose of this study was to investigate the involvement of the vasodilators bradykinin and des-Arg(9)-BK and kallikrein activity in post-exercise hypotension promoted by 35 min of cycle ergometer (CE) or circuit weight-training (CWT) bouts in normotensive and hypertensive individuals. A significant decrease in mean arterial pressure at 45 and 60 min after CE and 45 min after CWT was observed in normotensive individuals. Hypertensive values of mean arterial pressure were significantly reduced at 45 and 60 min after CE and at 60 min after CWT. Before exercise, plasma bradykinin concentrations and kallikrein activity were higher in hypertensive compared to normotensive volunteers. Kinin levels increased in the groups evaluated at the end of the training period and 60 min post-exercise. These data suggest that the kallikrein-kinin system may be involved in post-exercise hypotension in normotensive and hypertensive individuals subjected to CE and CWT bouts.

Forebrain regions associated with postexercise differences in autonomic and cardiovascular function during baroreceptor unloading

The cortical regions representing peripheral autonomic reactions in humans are poorly understood. This study examined whether changes in forebrain activity were associated with the altered physiological responses to lower body negative pressure (LBNP) following a single bout of dynamic exercise (POST-EX). We hypothesized that, compared with the nonexercised condition (NO-EX), POST-EX would elicit greater reductions in stroke volume (SV) and larger increases in heart rate (HR) and muscle sympathetic nerve activity (MSNA) during LBNP (5, 15, and 35 mmHg). Forebrain neural activity (n = 11) was measured using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. HR, SV, arterial blood pressure (ABP), and MSNA were collected separately. Compared with NO-EX, baseline ABP was reduced, whereas HR and total vascular conductance (TVC) were elevated in POST-EX (P < 0.05). In both conditions, 5 mmHg LBNP did not elicit a change (from baseline) in any physiological parameter. Compared with NO-EX, 35 mmHg LBNP-mediated decreases in SV and TVC produced greater increases in HR and MSNA during POST-EX (P < 0.05). The right posterior insula and dorsal anterior cingulate cortex demonstrated a larger decrease in BOLD at 5 mmHg LBNP but greater BOLD increase at 15 and 35 mmHg LBNP POST-EX vs. NO-EX (P < 0.005). Conversely, the thalamus and ventral medial prefrontal cortex displayed the opposite BOLD activity pattern (i.e., larger increase at 5 mmHg LBNP but greater decrease at 15 and 35 mmHg LBNP POST-EX vs. NO-EX). Our findings suggest that discrete forebrain regions may be involved with the generation of baroreflex-mediated sympathetic and cardiovascular responses elicited by moderate LBNP.

Effects of the menstrual cycle and sex on postexercise hemodynamics

Factors associated with the menstrual cycle, such as the endogenous hormones estrogen and progesterone, have dramatic effects on cardiovascular regulation. It is unknown how this affects postexercise hemodynamics. Therefore, we examined the effects of the menstrual cycle and sex on postexercise hemodynamics. We studied 14 normally menstruating women [24.0 (4.2) yr; SD] and 14 men [22.5 (3.5) yr] before and through 90 min after cycling at 60% .VO2(peak) for 60 min. Women were studied during their early follicular, ovulatory, and mid-luteal phases; men were studied once. In men and women during all phases studied, mean arterial pressure was decreased after exercise throughout 60 min (P < 0.001) postexercise and returned to preexercise values at 90 min (P = 0.089) postexercise. Systemic vascular conductance was increased following exercise in both sexes throughout 60 min (P = 0.005) postexercise and tended to be elevated at 90 min postexercise (P = 0.052), and femoral vascular conductance was increased following exercise throughout 90 min (P < 0.001) postexercise. Menstrual phase and sex had no effect on the percent reduction in arterial pressure (P = 0.360), the percent rise in systemic vascular conductance (P = 0.573), and the percent rise in femoral vascular conductance (P = 0.828) from before to after exercise, nor did the pattern of these responses differ across recovery with phase or sex. This suggests that postexercise hemodynamics are largely unaffected by sex or factors associated with the menstrual cycle.