© 2000 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Nitric oxide contributes to the regulation of vasomotor tone but does not modulate O2-consumption in exercising swine
Experimental Cardiology, Thoraxcenter, Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlands
* Corresponding author. Tel.: +31-10-408-8029; fax: +31-10-408-9494 duncker{at}tch.fgg.eur.nl
Received 17 February 2000; accepted 22 May 2000
 |
Abstract |
|---|
 Top Abstract 1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
Objective: The role of nitric oxide (NO) in the regulation of vasomotor tone and tissue O2-consumption is incompletely understood. We therefore determined the contribution of endogenous NO to regulation of systemic, pulmonary and coronary vasomotor tone and myocardial (MVO2) and whole body (BVO2) O2-consumption in exercising swine. Methods and results: Exercise (1–5 km/h) up to 85% of maximum heart rate in 11 swine produced a 4-fold increase in BVO2, which was accommodated for by 2-fold increases in both cardiac output (CO) and body O2-extraction. The NO synthase inhibitor N
-nitro-L-arginine (NLA, 20 mg/kg, i.v.) increased mean aortic pressure by 30 mmHg both at rest and during exercise, due to a decrease in systemic vascular conductance from 37±2 to 22±1 ml/min mmHg–1 at rest and from 88±3 to 60±3 ml/min mmHg–1 at 5 km/h (all P
0.05 versus control). NLA produced vasoconstriction at rest and at 5 km/h in virtually all regional beds but did not affect the exercise-induced redistribution of CO. NLA increased mean pulmonary artery pressure from 15±1 to 21±1 mmHg at rest and from 30±2 to 40±2 mmHg at 5 km/h, due to a decrease in pulmonary vascular conductance (all P0.05). BVO2 remained unchanged and consequently the decrease in CO resulted in a compensatory increase in O2-extraction. NLA in a dose of 40 mg/kg produced similar responses. NLA had no significant effect on myocardial O2-demand or MVO2 either at rest or during exercise, but decreased coronary vascular conductance which resulted in a decrease in coronary venous PO2 from 24.5±1.1 to 21.9±0.8 mmHg at rest and from 23.5±0.5 to 21.0±0.6 mmHg at 5 km/h (all P0.05). Conclusions: Endogenous NO dilates the systemic, pulmonary and coronary vascular bed, but does not modify MVO2 or BVO2 in swine at rest and during exercise.
KEYWORDS Coronary circulation; Nitric oxide; Oxygen consumption; Pulmonary circulation; Vasoconstriction/dilation
|
1 Introduction |
|---|
|
TopAbstract1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
The role of nitric oxide (NO) in the regulation of coronary vasomotor tone under basal conditions and during increased myocardial metabolic demand is incompletely understood. Several studies in awake dogs have shown that inhibition of NO has no effect on coronary blood flow (CBF) at rest [1–3] and during treadmill exercise [3,4], although one study reported a small decrease in CBF at rest [4]. In contrast, the contribution of NO to the regulation of vasomotor tone in the coronary resistance vessels is more apparent in the human heart, both at rest [5–7] and during metabolic stimulation via atrial pacing [5,6] or handgrip exercise [7]. These studies indicate the existence of important species differences with respect to the role of NO in the regulation of CBF. Recently, we reported that similar to humans, but unlike the dog [8], the coronary circulation of swine maintains the balance between O2-supply and O2-demand during moderate exercise so that myocardial O2-extraction (MEO2) does not increase during exercise up to 85% of maximum heart rate (HRmax) [9]. In the latter study we also observed that the maintained MEO2 in the porcine heart during exercise was principally the result of feedforward β-adrenergic vasodilation [9]. Since NO has been implicated in the coronary vasodilation produced by pharmacological β-adrenoceptor stimulation [1], the first aim of the present study was to test the hypothesis that NO contributes to the β-adrenergic feed-forward vasodilation in the swine heart during treadmill exercise.
Nitric oxide has also been implicated in the regulation of vasomotor tone in the systemic vascular bed, as inhibition of NO production results in a marked increase in arterial blood pressure and systemic vasoconstriction [10–14]. However, the role of NO in the regulation of vasomotor tone in the various organs and tissues of the body and the redistribution during increased metabolic demand such as exercise has only been studied during moderate exercise (65–70% of HRmax) in dogs [15]. NO may also contribute to the maintenance of a low pulmonary vascular resistance, although this observation appears to be species-dependent, as inhibition of NO resulted in pulmonary vasoconstriction in awake sheep [14] and men [11], but not in awake dogs [16]. The role of NO in the pulmonary vasodilator response to exercise has sofar only been studied at a single level of exercise in sheep [14]. Consequently, the second aim of the present study was to test the hypothesis that NO regulates vasomotor tone in regional, systemic and pulmonary beds, both at rest and during exercise up to 85% of HRmax in swine.
Recent studies have also suggested a role for NO in the regulation of tissue O2-consumption. Thus, in awake dogs inhibition of NO increased whole body O2-consumption (BVO2) [10] and myocardial O2-consumption (MVO2) [3,4], while NO inhibition had no effect on BVO2 in awake humans [17]. There is no study in humans which has investigated NO's role in the regulation of MVO2, and there is sofar only one study in anesthetized swine, that suggests an unchanged MVO2 following inhibition of NO [18]. However, the latter data have to be viewed with caution as pentobarbital anesthesia may abolish the effects of NO on MVO2 [10]. Furthermore, there is evidence that the effects of NO inhibition on MVO2 in the canine heart increase progressively with increasing levels of exercise [4], so that in anesthetized swine the effects of inhibition of NO on MVO2 may have gone unnoticed. Hence, the third aim of the present study was to test the hypothesis that NO modulates MVO2 and BVO2 in swine at rest and during treadmill exercise.
|
2 Methods |
|---|
|
TopAbstract1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
2.1 Surgical procedures
All experimental procedures have been described extensively [9,19–21]. In brief, 15 laboratory-conditioned Landrace-Yorkshire swine (5
and 10 
; 23±1 kg at the time of surgery and 29±1 kg at the time of study) were sedated (ketamine, 20 mg/kg, i.m.), anesthetized (thiopental, 10 mg/kg, i.v.), intubated and ventilated with O2 and N2O to which 0.2–1% (v/v) isoflurane was added [9,19]. Anesthesia was maintained with midazolam (2 mg/kg+1 mg/kg h–1, i.v.) and fentanyl (10 µg/kg h–1, i.v.). Under sterile conditions, the chest was opened via the fourth left intercostal space and a polyvinylchloride catheter was inserted into the aortic arch for measurement of mean aortic pressure (MAP, Combitrans® pressure transducers, Braun) and blood sampling to determine PO2, PCO2 and pH (Acid-Base Laboratory Model 505, Radiometer), O2-saturation and hemoglobin concentration (OSM2, Radiometer), for computation of O2- and CO2-contents, O2-delivery (DO2), O2-consumption, and CO2-production [9,19]. After the pericardium was opened an electromagnetic flow probe (14–15 mm, Skalar) was positioned around the ascending aorta for measurement of cardiac output (CO), and a microtipped pressure-transducer (Konigsberg Instruments) was inserted into the left ventricle (LV) via the apex. Polyvinylchloride catheters were inserted into the LV to calibrate the Konigsberg transducer pressure signal [9,19], and into the left atrium to measure pressure and inject radioactive microspheres to determine tissue flows [20,21]. Catheters were inserted into the pulmonary artery to measure pressure, administer drugs and collect mixed venous samples. An angio-catheter was inserted into the anterior interventricular vein for sampling in seven swine, while a Doppler flow probe (2.0–3.0 mm, Crystal Biotech) was placed around the proximal left anterior descending coronary artery (LADCA) [9]. Catheters were tunneled subcutaneously to exit at the back and animals were allowed to recover for 1 week before experiments were performed [9,19]. All experiments were performed in accordance with the Guide for the Care and Use of Laboratory Animals as published by the US National Institute of Health (NIH Publication N0. 85-23, revised 1996) and under the regulations of the Animal Care Committee of the Erasmus University Rotterdam. Experimental protocols were performed 1–5 weeks after surgery.
2.2 Experimental protocols
After hemodynamic measurements (lying and standing), blood samples (lying) and rectal temperature (standing) were obtained in 11 swine, a five-stage treadmill exercise protocol was begun (1–5 km/h); data were obtained during the last 30 s of each 2–3-min exercise stage [9,19]. Radioactive microspheres were injected at rest (lying) and during exercise at 5 km/h in seven swine [20,21]. After 60 min of rest, N-nitro-L-arginine (NLA, 20 mg/kg in 120 ml saline, i.v.) was infused over 30 min. Fifteen minutes following completion of the infusion, the exercise protocol was repeated. On another day (separated by at least 72 h) two control exercise periods separated by 90 min of rest were performed to confirm reproducibility of exercise responses [9,19]. Reliable left atrial phasic pressure measurements could not be obtained in five animals.
Efficacy of NO synthase inhibition (n=4), using sodium nitroprusside (SNP, 0.5–5.0 µg/kg min–1, i.v.) and ATP (0.05–0.5 mg/kg min–1, i.v.) before and after NLA (20 mg/kg, i.v.) was studied on a different day. Data were obtained during the last 30 s of infusion of each dose [9,19].
2.3 Data analysis
Digital recording and off-line analysis of hemodynamic, radioactive microsphere and metabolic data have been described extensively [9,19–21]. There were no statistical differences in responses of males and females and hence all data have been pooled. Statistical analysis was performed using two-way analysis of variance for repeated measures, followed by Dunnett's test (exercise effect) or Paired t-testing (treatment effect). Significance was accepted when P0.05 (two-tailed). Data are mean±S.E.M.
|
3 Results |
|---|
|
TopAbstract1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
3.1 Degree of NO synthase inhibition by NLA
ATP increased systemic vascular conductance (SVC=CO/MAP) and coronary vascular conductance (CVC=CBF/MAP) (Fig. 1). After NLA, the vasodilator responses were markedly blunted (Fig. 1). In contrast, the SNP-induced systemic and coronary vasodilation were not altered by NLA, indicating that the effects of NLA are specific to the endothelium-dependent vasodilation produced by ATP [22].
|
P3.2 Effect of NLA on responses to treadmill exercise
3.2.1 Systemic and pulmonary circulation
During exercise (1–5 km/h) CO increased principally due to a doubling of HR (reaching 85% of HRmax at 5 km/h) (Table 1), as stroke volume (SV) increased only up to
10% at 1–3 km/h (not shown). Since LV systolic pressure (LVSP) increased, the small increase in SV resulted from increases in mean left atrial pressure (MLAP) and LVdP/dtmax. Mean aortic pressure (MAP) did not change, because systemic vascular conductance more than doubled at 5 km/h. In contrast, mean pulmonary artery pressure (MPAP) doubled during exercise as pulmonary vascular conductance (PVC=CO/(MPAP-MLAP)) increased up to 25–30% at 5 km/h.
|
Under resting conditions, NLA increased MAP by 30%, due to a decrease in SVC as cardiac output deceased. The latter was due to a decrease in HR, which was probably baroreceptor reflex-mediated. MPAP also increased due a decrease in PVC. In the presence of NLA, the exercise-induced increases in CO and SVC were unmitigated, but the exercise-induced increase in PVC was blunted (Table 1).
3.2.2 Coronary circulation
Exercise did not alter coronary venous (cv) PO2 (Fig. 2), PCO2, pH, SO2, or O2-content (not shown). MVO2 and MDO2 (CBFxarterial O2-content) increased in parallel, so that MEO2 (MVO2/MDO2) remained unchanged (Fig. 2). After NLA, CVC decreased, thereby limiting MDO2 at each level of MVO2, The decrease in MDO2 necessitated an increase in MEO2 and hence resulted in a lower cvPO2.
|
NLA did not affect mean transmural myocardial blood flow in the LV free wall (n=7) either at rest (1.30±0.06 ml/min g–1) or during exercise at 5 km/h (3.53±0.44 ml/min g–1), but redistributed blood flow from the outer to the inner layer as the endo/epi blood flow ratio increased from 0.96±0.08 to 1.31±0.08 at 5 km/h, likely due to the increase in aortic pressure in conjunction with the decrease in heart rate. In contrast, NLA decreased mean transmural blood flow in the right ventricular free wall from 1.01±0.07 to 0.85±0.06 ml/min g–1 at rest and from 4.11±0.44 to 3.51±0.51 ml/min g–1 at 5 km/h (P
0.05), but did not affect the transmural distribution. NLA did not affect resting blood flows in either left or right atrium, but decreased atrial flows at 5 km/h.
3.2.3 Regional blood flows
Exercise increased skeletal muscle flow (Fig. 3), varying from 5-fold in predominantly white fiber muscle to 20-fold in predominantly red fiber muscle [8]. Total brain flow remained unchanged although cerebellar flow increased (Table 2). Flow to various other organs decreased except for adrenals. Arterio-venous anastomotic (AVA) flow (represented by lung flow [20]) tripled, while abdominal skin flow increased slightly.
|
|
Skeletal muscle flow was not affected by NLA (Fig. 3). NLA decreased flow to most other organs at rest and/or during exercise, except for spleen, colon and skin (Table 2), and virtually abolished the exercise-induced increase in AVA flow. NLA decreased vascular conductance in most organs and tissues at rest and during exercise, but the exercise-induced alterations in conductance were unchanged in most organs, except in the pancreas, bone and AVAs (Table 2).
3.2.4 Metabolism
3.2.4.1 Body O2-consumption.
During exercise arterial PCO2 decreased from 44±1 mmHg at rest to 40±1 mmHg at 5 km/h, while pH increased from 7.46±0.01 to 7.49±0.01 (both P0.05). Arterial SO2 did not change (Fig. 4), but Hb and hence arterial O2-content increased 14±2% (P0.05) at the highest exercise level compared to resting conditions. During exercise mixed venous SO2 decreased, reflecting the increase in arteriovenous O2-content difference from 2.12±0.11 to 3.80±0.08 mmol/l (P0.05), while mixed venous PCO2 increased from 52±1 to 55±2 mmHg (P0.05). BVO2 quadrupled which was accommodated by a near doubling of CO and arterio–mixed venous O2-content difference.
|
NLA did not affect arterial Hb or SO2 but decreased mixed venous SO2, reflecting an increased body O2-extraction. The latter compensated for the lower CO so that BVO2 was not different from control at rest and during exercise. However, NLA increased the respiratory quotient as the BVO2–BVCO2 relation rotated counter-clockwise (Fig. 5), compatible with a shift in substrate use. The lack of effect of NLA on BVO2 was not because of insufficient dosing because 40 mg/kg (n=4) produced similar hemodynamic (not shown) and metabolic responses as 20 mg/kg. Thus after 40 mg/kg NLA, BVO2 was 8.0±1.1 and 29.3±3.4 mmol/min at rest and 5 km/h versus 7.3±1.0 and 27.4±2.8 mmol/min at rest and 5 km/h during control.
|
Intravenous infusion of SNP did not affect BVO2 in five resting swine (6.9±0.4 mmol/min at baseline, and 7.0±0.4 and 7.7±0.5 mmol/min during 3 and 5 µg/kg min–1, respectively).
3.2.4.2 Myocardial O2-consumption.
NLA had no effect on MVO2, the relation between MVO2 and a number of indices of myocardial O2-demand (Fig. 6), and the relation between MVO2 and myocardial VCO2 (Fig. 5).
|
3.3 Reproducibility of exercise-responses
The second period of exercise, 90 min after completion of the first exercise period when all hemodynamic variables had returned to baseline resting values, resulted in nearly identical changes in systemic, pulmonary and coronary hemodynamics (Table 3 and Fig. 2), BVO2 (Fig. 4) and MVO2 (Fig. 6).
|
|
4 Discussion |
|---|
|
TopAbstract1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
The major findings of this study in awake swine are that: (i) endogenous NO exerts a vasodilator influence on the systemic, pulmonary and coronary circulation, largely independent of the level of exercise; (ii) NO's vasodilator influence in the systemic circulation is present in virtually all tissues; (iii) NO mediates exercise-induced increases in AVA flow; (iv) endogenous NO does not modulate MVO2 or BVO2, although a shift in substrate utilization may mask a small effect on BVO2.
4.1 Role of NO in the regulation of vasomotor tone
4.1.1 Systemic circulation
NO plays a major role in vasomotor tone regulation of the systemic bed. Thus, NO inhibition markedly increases systemic vascular resistance (i.e., decreases SVC) and MAP [10–14]. In awake rats [13], rabbits [12] and dogs [15], NO inhibition decreased perfusion of kidneys (16% [12], 47% [13] and 30% [15]), pancreas (63% [15]), stomach (22% [12], 61% [13]), small intestine (0% [12], 53% [13], 50% [15]), large intestine (13% [12], 48% [15]), and brain (11% [12], 23% [13]), but not of spleen or skin. We also observed decreases in perfusion of brain, kidneys, adrenals, urinary bladder, pancreas, and femur, but not of skin and spleen, and minimal decreases in perfusion in the gastrointestinal tract. In general, NLA's effects on tissue perfusion and vasomotor tone were similar at rest and during strenuous exercise (85% of maximum heart rate), which suggests that NO contributes to vasodilation in a tonic fashion. Similar to dogs exercising at 65–70% of maximum heart rate [15], endogenous NO did not alter the exercise-induced redistribution of cardiac output in the present study in swine.
Endogenous NO exerts a basal vasodilator influence in skeletal muscle. Thus, NO synthase inhibition decreased vascular conductance in skeletal muscle of awake resting rabbits [12], dogs [15,23], humans [17,24–26] and swine (present study). The vasoconstriction causes a decrease in resting skeletal muscle flow [15,23–26], particularly after regional NO inhibition [24–26], whereas after intravenous administration the increase in vasomotor tone in some skeletal muscle is often counterbalanced by the increase in aortic pressure, thereby maintaining resting flow [12,15,17] (present study). In contrast to the pivotal role of NO in vasomotor tone regulation at rest, NO is not mandatory for the exercise-induced active skeletal muscle hyperemia, so that muscle flow after NO inhibition is not different from that during control exercise in dogs [15,23], humans [17,26], and swine (present study). In contrast, NO inhibition generally causes a decrease in plethysmography-measured exercise forearm flow [27], but to obtain these data it is necessary to interrupt the exercise. Radegran and Saltin [26] using the Doppler technique which permits measurement during exercise, showed that NO inhibition did not affect exercise leg flow but reduced flow during recovery. This last study suggests that plethysmography studies reflect NO's contribution during recovery from rather than during exercise [26]. Similarly, Brock et al. [28] reported that NO inhibition blunted peak reactive hyperemia following a single forearm-muscle contraction, although their findings could also indicate a role for NO in the initial hyperemic vasodilator response. It has been reported that NO's role in flow regulation may vary among different muscle fiber types in rats, being the greatest in red fiber muscle [29]. However, the present study in swine does not support those findings as NLA did not decrease flow to either red or white fiber containing muscle either at rest or during exercise.
AVAs are present in the skin and contribute to body temperature control [30]. Because they are 30–90 µm in diameter, 15-µm microspheres pass through these vessels and are trapped in the lungs [20]. Microspheres also reach the lungs via bronchial artery flow. However, bronchial artery flow amounts to only 1–1.5% of cardiac output [31]. Since total lung flow was 7% of CO at rest and 23% during exercise, it follows that the majority of microspheres trapped in the lungs must have arrived via AVAs. Consequently, ‘lung’ flow represents principally AVA flow. NLA did not modify resting AVA flow but virtually abolished the exercise-induced increase in AVA flow, indicating that NO mediated the exercise-induced AVA vasodilation. In three swine we observed that core temperature (measured with an intrathoracic probe), increased 0.33±0.03°C above its resting value of 39.1±0.1°C during exercise at 4 km/h (unpublished data). These findings suggest that the exercise-induced AVA vasodilation is the result of the increase in body core temperature and that NO is the unidentified mediator of AVA dilation during the rise of body temperature [30].
4.1.2 Pulmonary circulation
Exogenous NO produces pulmonary vasodilation [32], but the role of endogenous NO in maintaining the high basal pulmonary vascular conductance remains controversial. Thus, while NO inhibition did not affect PVC in anesthetized rats [33], and the pulmonary pressure–flow relations in awake dogs [16], PVC decreased in awake sheep [14] and healthy volunteers [11] by 25–30%. Contrary to rats and dogs, but similar to humans and sheep, NO inhibition increased MPAP by 30–40% and decreased PVC by 20–30% in awake swine at rest.
The exercise-induced increase in CO in the present study exceeded the increase in pulmonary driving-pressure (MPAP–MLAP), so that PVC increased by 25–30%, which corresponds well with the 30% exercise-induced increase in PVC observed in other quadrupeds such as sheep [14]. In sheep, NLA decreased basal PVC but did not alter the exercise-induced pulmonary vasodilation during exercise [14]. In the present study, NO inhibition similarly decreased basal PVC and, in addition, blunted the exercise-induced pulmonary vasodilation suggesting that endogenous NO contributes to the exercise-induced pulmonary vasodilation in swine.
4.1.3 Coronary circulation
CBF is tightly regulated to maintain a consistently high level of MEO2. Consequently, any increase in MVO2 must be met by an equivalent increase in CBF. In dogs the exercise-induced increase in CBF does not fully match the increased MVO2, so that even during moderate exercise MEO2 increases and cvPO2 decreases [8]. In contrast, in humans MEO2 and cvPO2 change minimally at moderate levels of exercise, while MEO2 increases and cvPO2 decreases during strenuous exercise [8]. Up to moderate exercise levels, swine resemble humans more closely than dogs but, in contrast to dogs and man, swine also maintain a constant level of MEO2 and cvPO2 during strenuous exercise, implying that exercise-induced increases in MDO2 match the increases in MVO2 [9]. A decrease in cvPO2 could represent an error signal needed for negative feedback metabolic control, but data in swine indicate that a decrease in cvPO2 is not mandatory for the increase in CBF during heavy exercise, due to increased importance of β-adrenergic feedforward vasodilation [9]. Since NO inhibition attenuates the coronary vasodilation by pharmacological stimulation of β1,2-adrenoceptors [1], we hypothesized that NO also contributes to exercise-induced β-adrenergic feedforward coronary vasodilation. Indeed, in the present study endogenous NO exerted a vasodilator influence in swine both at rest and during exercise. However, NO was not mandatory for the exercise-induced vasodilation as the cvPO2 was not further altered by exercise in the presence of NLA. Similarly, endogenous NO dilates human coronary resistance vessels under basal conditions [5–7] and during metabolic stimulation [6,7], but generally NO inhibition does not blunt the metabolic stimulation-induced coronary vasodilation [6,7]. In contrast, NO appears not to be mandatory for regulation of CBF in dogs as NO inhibition does not affect CBF at rest [1–3] or during treadmill exercise [4,5], although one study reported a small decrease in CBF at rest and during light exercise [4]. Importantly, in all three species NO inhibition does not impair metabolic coronary vasodilation indicating that either NO does not contribute or that other vasodilator mechanisms compensate.
4.2 Metabolic effects of endogenous NO
The role of NO in the regulation of tissue VO2 was initially suggested by observations that NO inhibits enzymes of the respiratory chain [34]. In vitro studies support the contention that endogenous NO levels modify VO2 [34], but in vivo studies are equivocal. In awake resting dogs, Hintze and co-workers reported that NLA (30 mg/kg, i.v.) increased BVO2 by 20–40% [10]. In contrast, inhibition of endogenous NO did not affect BVO2 in anesthetized dogs [10,35,36], underscoring the importance of studies in awake animals. Indeed, NO inhibition did also not affect MVO2 in anesthetized dogs [37,38], whereas in awake dogs NO inhibition increased MVo2 at a given cardiac workload in most [3,4], though not all [39], studies. However, the importance of anesthesia is not entirely clear, as one study in awake dogs failed to observe an increase in hindlimb VO2 [23], whereas another study in pentobarbital-anesthetized dogs reported an increase in hindlimb VO2 [35].
In the present study we found no increase in BVO2 or MVO2 after NLA suggesting that levels of endogenous NO do not modulate VO2 in awake swine both at rest and during exercise. NLA may have caused a shift in substrate utilization, which can result in a small increase in P:O ratio [34] and thereby mask a subtle effect of NO on ATP utilization. However, this cannot account for the 20–40% increases in BVO2 that were reported for awake dogs [10]. There could be several reasons for the differences between the present and that previous study [10] regarding the effect of NO inhibition on VO2. Firstly, the dose of 20 mg/kg of NLA we initially used is lower than the 30 mg/kg dose used in the canine study [10], so that it could be argued that insufficient dosing in the present study was responsible for the lack of effect of NLA on BVO2. This is unlikely, however, in view of the marked effects of this dose of NLA on vasomotor tone in the various beds and because the 40-mg/kg dose had also no effect on BVO2. Secondly, it could be argued that after administration of NLA not enough time was allowed to observe an effect of NO inhibition on VO2. This is also unlikely, as Shen et al. [10] demonstrated that the NLA-induced elevation of BVO2 occurred within 15 min after completion of administration and remained stable up to 120 min. In the present study we infused NLA over a 30-min period and allowed 15 min before measurements were made, during which time hemodynamic variables were stable. Since during infusion of the 40-mg/kg dose, 20 mg/kg had already been administered after 15 min (yielding a total of 30 min before measurements were obtained), it is unlikely that insufficient time was allowed to observe an effect. Thirdly, Shen et al. [10] reported that the 0.7°C increase in body temperature following administration of NLA in dogs, was, at least in part, responsible for the increase in BVO2. In contrast, NLA had no effect on temperature in the present study (39.2±0.2°C). Finally, it is possible that swine have a lower degree of NO synthase expression than dogs, so that inhibition of low levels of endogenous NO would have a minimal metabolic effect. However, this is an unlikely explanation since exogenous NO administration via SNP infusion had also no effect on BVO2. Taken together, our findings suggest that dogs and swine are different in their metabolic response to NO inhibition. Of importance, studies in resting and exercising humans have also failed to observe an increase in BVO2 [17], leg VO2 [26] or forearm VO2 [27] following NO inhibition, suggesting that the in vivo metabolic effects of NO are more prominent in dogs than in humans and swine. This suggests that loss of NO production as has been suggested to occur in severe heart failure [40] may not lead to an increased energy consumption in humans or swine as would be predicted based on data obtained in dogs.
Time for primary review 32 days.
|
Acknowledgements |
|---|
Rob van Bremen and John Dries are acknowledged for technical assistance. Dr. Duncker is supported by a Research Fellowship of the Royal Netherlands Academy of Arts and Sciences.
|
References |
|---|
|
TopAbstract1 Introduction2 Methods3 Results4 DiscussionReferences |
|---|
- Parent R., al-Obaidi M., Lavallee M. Nitric oxide formation contributes to β-adrenergic dilation of resistance coronary vessels in conscious dogs. Circ. Res. (1993) 73:241–251.
[Abstract/Free Full Text] - Smith T.P. Jr., Canty J.M. Jr. Modulation of coronary autoregulatory responses by nitric oxide. Evidence for flow-dependent resistance adjustments in conscious dogs. Circ. Res. (1993) 73:232–240.
[Abstract/Free Full Text] - Altman J.D., Kinn J., Duncker D.J., Bache R.J. Effect of inhibition of nitric oxide formation on coronary blood flow during exercise in the dog. Cardiovasc. Res. (1994) 28:119–124.
[Abstract/Free Full Text] - Bernstein R.D., Ochoa F.Y., Xu X., et al. Function and production of nitric oxide in the coronary circulation of the conscious dog during exercise. Circ. Res. (1996) 79:840–848.
[Abstract/Free Full Text] - Lefroy D.C., Crake T., Uren N.G., Davies G.J., Maseri A. Effect of inhibition of nitric oxide synthesis on epicardial coronary artery caliber and coronary blood flow in humans. Circulation (1993) 88:43–54.
[Abstract/Free Full Text] - Quyyumi A.A., Dakak N., Andrews N.P., Gilligan D.M., Panza J.A., Cannon R.O. III. Contribution of nitric oxide to metabolic coronary vasodilation in the human heart. Circulation (1995) 92:320–326.
[Abstract/Free Full Text] - Nishikawa Y., Kanki H., Ogawa S. Role of nitric oxide in coronary vasomotion during handgrip exercise. Am. Heart J. (1997) 134:967–973.[CrossRef][Web of Science][Medline]
- Laughlin M.H., Korthuis R., Duncker D.J., Bache R.J. Regulation and integration of multiple systems during exercise. Rowell L.B., Shepherd J.T., eds. (1996) New York: Oxford Press. 705–769. American physiological society handbook section 12.
- Duncker D.J., Stubenitsky R., Verdouw P.D. Autonomic control of vasomotion in the porcine coronary circulation during treadmill exercise: evidence for feed-forward β-adrenergic control. Circ. Res. (1998) 82:1312–1322.
[Abstract/Free Full Text] - Shen W., Xu X., Ochoa M., Zhao G., Wolin M.S., Hintze T.H. Role of nitric oxide in the regulation of oxygen consumption in conscious dogs. Circ. Res. (1994) 75:1086–1095.
[Abstract/Free Full Text] - Stamler J.S., Loh E., Roddy M.A., Currie K.E., Creager M.A. Nitric oxide regulates basal systemic and pulmonary vascular resistance in healthy humans. Circulation (1994) 89:2035–2040.
[Abstract/Free Full Text] - Humphries R.G., Carr R.D., Nicol A.K., Tomlinson W., O’Connor S.E. Coronary vasoconstriction in the conscious rabbit following intravenous infusion of L-NG-nitro-arginine. Br. J. Pharmacol. (1991) 102:565–566.[Web of Science][Medline]
- Sigmon D.H., Florentino-Pineda I., Van Dyke R.A., Beierwaltes W.H. Halothane impairs the hemodynamic influence of endothelium-derived nitric oxide. Anesthesiology (1995) 82:135–143.[CrossRef][Web of Science][Medline]
- Koizumi T., Gupta R., Banerjee M., Newman J.H. Changes in pulmonary vascular tone during exercise. Effects of nitric oxide (NO) synthase inhibition, L-arginine infusion, and NO inhalation. J. Clin. Invest. (1994) 94:2275–2282.[Web of Science][Medline]
- Shen W., Lundborg M., Wang J., et al. Role of EDRF in the regulation of regional blood flow and vascular resistance at rest and during exercise in conscious dogs. J. Appl. Physiol. (1994) 77:165–172.
[Abstract/Free Full Text] - Nishiwaki K., Nyhan D.P., Rock P., et al. N-Nitro-L-arginine and pulmonary vascular pressure-flow relationship in conscious dogs. Am. J. Physiol. (1992) 262:H1331–H1337.[Web of Science][Medline]
- Koller-Strametz J., Matulla B., Wolzt M., et al. Role of nitric oxide in exercise-induced vasodilation in man. Life Sci. (1998) 62:1035–1042.[CrossRef][Web of Science][Medline]
- Kirkeboen K.A., Naess P.A., Offstad J., Ilebekk A. Effects of regional inhibition of nitric oxide synthesis in intact porcine hearts. Am. J. Physiol. (1994) 266:H1516–H1527.[Web of Science][Medline]
- Stubenitsky R., Verdouw P.D., Duncker D.J. Autonomic control of cardiovascular performance and oxygen transport in awake swine at rest and during treadmill exercise. Cardiovasc. Res. (1998) 39:459–474.
[Abstract/Free Full Text] - Saxena P.R., Verdouw P.D. Tissue blood flow and localization of arteriovenous anastomoses in pigs with microspheres of four different sizes. Pfluegers Arch. (1985) 403:128–135.[CrossRef][Web of Science][Medline]
- Duncker D.J., Haitsma D.B., van der Geest I.E., et al. Systemic, pulmonary and coronary haemodynamic actions of the novel dopamine receptor agonist Z1046 in awake pigs at rest and during treadmill exercise. Br. J. Pharmacol. (1997) 120:1101–1113.[CrossRef][Web of Science][Medline]
- Kitakaze M., Node K., Komamura K., Minamino T., Kosaka H., Kuzuya T., Hori M. Intracoronary administration of adenosine triphosphate increases coronary flow and attenuates the severity of myocardial ischemic injury in dogs. Cardiovasc. Drugs Ther. (1999) 13:407–414.[CrossRef][Web of Science][Medline]
- O’Leary D.S., Dunlap R.C., Glover K.W. Role of endothelium-derived relaxing factor in hindlimb reactive and active hyperemia in conscious dogs. Am. J. Physiol. (1994) 266:R1213–R1219.[Web of Science][Medline]
- Vallance P., Collier J., Moncada S. Effects of endothelium-derived nitric oxide on peripheral arteriolar tone in man. Lancet (1989) ii:997–1000.
- Wilson J.R., Kapoor S. Contribution of endothelium-derived relaxing factor to exercise-induced vasodilation in humans. J. Appl. Physiol. (1993) 75:2740–2744.
[Abstract/Free Full Text] - Radegran G., Saltin B. Nitric oxide in the regulation of vasomotor tone in human skeletal muscle. Am. J. Physiol. (1999) 276:H1951–H1960.[Web of Science][Medline]
- Endo T., Imaizumi T., Tagawa T., Shiramoto M., Ando S., Takeshita A. Role of nitric oxide in exercise-induced vasodilation of the forearm. Circulation (1994) 90:2886–2890.
[Abstract/Free Full Text] - Brock R.W., Tschakovsky M.E., Shoemaker J.K., Halliwill J.R., Joyner M.J., Hughson R.L. Effects of acetylcholine and nitric oxide on forearm blood flow at rest and a single muscle contraction. J. Appl. Physiol. (1998) 85:2249–2254.
[Abstract/Free Full Text] - Hirai T., Visneski M.D., Kearns K.J., Zelis R., Musch T.I. Effects of NO synthase inhibition on the muscular blood flow response to treadmill exercise in rats. J. Appl. Physiol. (1994) 77:1288–1293.
[Abstract/Free Full Text] - Hales J.R.S., Molyneux G.S. Vasodilatation: vascular smooth muscle, peptides, autonomic nerves and endothelium. Vanhoutte P.M., ed. (1988) New York: Raven Press. 321–332.
- Baile E.M., Nelems J.M., Schulzer M., Pare P.D. Measurement of regional bronchial arterial blood flow and bronchovascular resistance in dogs. J. Appl. Physiol. (1982) 53:1044–1049.
[Abstract/Free Full Text] - Barnes P.J., Liu S.F. Regulation of pulmonary vascular tone. Pharmacol. Rev. (1995) 47:87–131.[Web of Science][Medline]
- Oka M., Hasunuma K., Webb S.A., Stelzner T.J., Rodman D.M., McMurtry I.F. EDRF suppresses an unidentified vasoconstrictor mechanism in hypertensive rat lungs. Am. J. Physiol. (1993) 264:L587–L597.[Web of Science][Medline]
- Wolin M.S., Xie Y.W., Hintze T.H. Nitric oxide as a regulator of tissue oxygen consumption. Curr. Opin. Nephrol. Hypertens. (1999) 8:97–103.[CrossRef][Web of Science][Medline]
- King C.E., Melinyshyn M.J., Mewburn J.D., et al. Canine hindlimb blood flow and O2 uptake after inhibition of EDRF/NO synthesis. J. Appl. Physiol. (1994) 76:1166–1171.
[Abstract/Free Full Text] - Crystal G.J., Zhou X., Halim A.A., Alam S., El-Orbany M., Salem M.R. Nitric oxide does not modulate whole body oxygen consumption in anesthetized dogs. J. Appl. Physiol. (1999) 86:1944–1949.
[Abstract/Free Full Text] - Sadoff J.D., Scholz P.M., Weiss H.R. Endogenous basal nitric oxide production does not control myocardial oxygen consumption or function. Proc. Soc. Exp. Biol. Med. (1996) 211:332–338.[CrossRef][Medline]
- Crystal G.J., Gurevicius J. Nitric oxide does not modulate myocardial contractility acutely in in situ canine hearts. Am. J. Physiol. (1996) 270:H1568–H1576.[Medline]
- Sherman A.J., Davis C.A. III, Klocke F.J., et al. Blockade of nitric oxide synthesis reduces myocardial oxygen consumption in vivo. Circulation (1997) 95:1328–1334.
[Abstract/Free Full Text] - Wang J., Seyedi N., Xu X.B., Wolin M.S., Hintze T.H. Defective endothelium-mediated control of coronary circulation in conscious dogs after heart failure. Am. J. Physiol. (1994) 266:H670–H680.[Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  D. J. Duncker and R. J. Bache Regulation of Coronary Blood Flow During Exercise Physiol Rev, July 1, 2008; 88(3): 1009 - 1086. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. M. McAllister, S. C. Newcomer, E. R. Pope, J. R. Turk, and M. H. Laughlin Effects of chronic nitric oxide synthase inhibition on responses to acute exercise in swine J Appl Physiol, January 1, 2008; 104(1): 186 - 197. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. J. Duncker and D. Merkus Exercise hyperaemia in the heart: the search for the dilator mechanism J. Physiol., September 15, 2007; 583(3): 847 - 854. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Merkus, B. Houweling, V. J. de Beer, Z. Everon, and D. J. Duncker Alterations in endothelial control of the pulmonary circulation in exercising swine with secondary pulmonary hypertension after myocardial infarction J. Physiol., May 1, 2007; 580(3): 907 - 923. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Merkus, O. Sorop, B. Houweling, F. Boomsma, A. H. van den Meiracker, and D. J. Duncker NO and prostanoids blunt endothelin-mediated coronary vasoconstrictor influence in exercising swine Am J Physiol Heart Circ Physiol, November 1, 2006; 291(5): H2075 - H2081. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. Houweling, D. Merkus, M. M. D Dekker, and D. J Duncker Nitric oxide blunts the endothelin-mediated pulmonary vasoconstriction in exercising swine J. Physiol., October 15, 2005; 568(2): 629 - 638. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Zong, J. D. Tune, and H. F. Downey Mechanisms of Oxygen Demand/Supply Balance in the Right Ventricle Experimental Biology and Medicine, September 1, 2005; 230(8): 507 - 519. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 X. Zhao, G. He, Y.-R. Chen, R. P. Pandian, P. Kuppusamy, and J. L. Zweier Endothelium-Derived Nitric Oxide Regulates Postischemic Myocardial Oxygenation and Oxygen Consumption by Modulation of Mitochondrial Electron Transport Circulation, June 7, 2005; 111(22): 2966 - 2972. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Westerhof Nitric oxide and efficiency of the right heart Cardiovasc Res, December 1, 2004; 64(3): 379 - 380. [Full Text] [PDF]
|
|
|
|
|
|
D. Merkus, B. Houweling, A. Zarbanoui, and D. J. Duncker Interaction between prostanoids and nitric oxide in regulation of systemic, pulmonary, and coronary vascular tone in exercising swine Am J Physiol Heart Circ Physiol, March 1, 2004; 286(3): H1114 - H1123. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Merkus, B. Houweling, A. Mirza, F. Boomsma, A. H van den Meiracker, and D. J Duncker Contribution of endothelin and its receptors to the regulation of vascular tone during exercise is different in the systemic, coronary and pulmonary circulation Cardiovasc Res, September 1, 2003; 59(3): 745 - 754. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Z. Kojic, U. Flogel, J. Schrader, and U. K. M. Decking Endothelial NO formation does not control myocardial O2 consumption in mouse heart Am J Physiol Heart Circ Physiol, June 5, 2003; 285(1): H392 - H397. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Merkus, D. B. Haitsma, T.-Y. Fung, Y. J. Assen, P. D. Verdouw, and D. J. Duncker Coronary blood flow regulation in exercising swine involves parallel rather than redundant vasodilator pathways Am J Physiol Heart Circ Physiol, June 5, 2003; 285(1): H424 - H433. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. L. Brutsaert Cardiac Endothelial-Myocardial Signaling: Its Role in Cardiac Growth, Contractile Performance, and Rhythmicity Physiol Rev, January 1, 2003; 83(1): 59 - 115. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. B. Haitsma, D. Merkus, J. Vermeulen, P. D. Verdouw, and D. J. Duncker Nitric oxide production is maintained in exercising swine with chronic left ventricular dysfunction Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2198 - H2209. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. B Haitsma, D. Bac, N. Raja, F. Boomsma, P. D Verdouw, and D. J Duncker Minimal impairment of myocardial blood flow responses to exercise in the remodeled left ventricle early after myocardial infarction, despite significant hemodynamic and neurohumoral alterations Cardiovasc Res, December 1, 2001; 52(3): 417 - 428. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. B. Haitsma, D. Merkus, J. Vermeulen, P. D. Verdouw, and D. J. Duncker Nitric oxide production is maintained in exercising swine with chronic left ventricular dysfunction Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2198 - H2209. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||