Nitric oxide and thermoregulation during exercise in the horse

Mills, Paul C., David J. Marlin, Caroline M. Scott, andNicola C. Smith. Nitric oxide and thermoregulation during exercise in the horse. J. Appl. Physiol. 82(4):1035-1039, 1997.The effect of inhibition of nitric oxideproduction on sweating rate (SR) and on core, rectal, and tail skintemperatures was measured in five Thoroughbred horses during exerciseof variable intensity on a high-speed treadmill. A standard exercisetest consisting of three canters [~55% maximumO₂ uptake(O_{2 max})], withwalking (~9%O_{2 max}) and trotting(~22% O_{2 max})between each canter, was performed twice (control or test), in randomorder, by each horse.N^G-nitro-L-arginine methyl ester(L-NAME; 20 mg/kg), acompetitive inhibitor of nitric oxide synthase, was infused into thecentral circulation and induced a significant reduction in the SRmeasured on the neck (31.6 ± 6.4 vs. 9.7 ± 4.2 g · min¹ · m²;69%) and rump (14.7 ± 5.2 vs. 4.8 ± 1.6 g · min¹ · m²;67%) of the horses during canter (P < 0.05). Significant increases in core, rectal, and tailskin temperatures were also measured (P < 0.05).L-Arginine (200 mg/kg iv)partially reversed the inhibitory effects ofL-NAME on SR, but core, rectal,and tail skin temperatures continued to increase(P < 0.05), suggesting a cumulationof body heat. The results support the contention that nitric oxidesynthase inhibition diminishes SR, resulting in elevated core andperipheral temperatures leading to deranged thermoregulation duringexercise. The inhibition of sweating byL-NAME may be related toperipheral vasoconstriction but may also involve the neurogenic controlof sweating.

     

Nitric oxide metabolites in exhaled breath condensate in young people

Exhaled breath samples were taken from students of the Medical Academy and condensed. The total nitrite and nitrate concentration (NNC) was measured in the condensed samples. At rest, smoking young men show a tendency to a lower NNC as compared to nonsmoking young men; smoking young women at rest, on the contrary, have a significantly higher NNC as compared to nonsmoking young women. Under psychoemotional stress, the NNC decreases in both young men and young women. Subjects with the maximum indices of systolic blood pressure (BP_s) show a significantly lower NNC as compared to subjects with the minimum BP_s indices.     

Ventilatory response during incremental exercise tests in weight lifters and endurance cyclists

The effect of a progressively increasing work rate (15 W X min-1) up to exhaustion on the time course of O2 uptake (VO2), ventilation (VE) and heart rate (HR) has been studied in weight lifters (WL) in comparison to endurance cyclists (Cycl) and sedentary controls (Sed). VO2 and VE were measured as average value of 30-s intervals by a semiautomatic open circuit method. VO2max was 2.55 +/- 0.33; 4.29 +/- 0.53 and 2.86 +/- 0.19 l X min-1 in WL, Cycl and Sed respectively. With time and work rate, while VO2 and HR increased linearly, VE changed its slope at two levels. The 1st VE change occurred at a work load corresponding to a mean (+/- SD) VO2 of 1.50 +/- 0.26; 1.93 +/- 0.34; and 1.23 +/- 0.14 l X min-1 in WL, Cycl, and Sed respectively. VO2 values corresponding to the second VE change of slope were 2.18 +/- 0.32 in WL; 3.48 +/- 0.53 in Cycl and 2.17 +/- 0.28 l X min-1 in Sed. The first change of slope might be the consequence of the different readjustment of VO2 on-response and hence of early lactate in the different subjects. The second change seems to be comparable to the conventional anaerobic threshold and is achieved in all subjects when VE vs time slope is 7-10 l X min-1/min of exercise.     

Dynamic cerebral autoregulation during exhaustive exercise in humans

We investigated whether dynamic cerebral autoregulation is affected by exhaustive exercise using transfer-function gain and phase shift between oscillations in mean arterial pressure (MAP) and middle cerebral artery (MCA) mean blood flow velocity (V(mean)). Seven subjects were instrumented with a brachial artery catheter for measurement of MAP and determination of arterial Pco(2) (Pa(CO(2))) while jugular venous oxygen saturation (Sv(O(2))) was determined to assess changes in whole brain blood flow. After a 10-min resting period, the subjects performed dynamic leg-cycle ergometry at 168 +/- 5 W (mean +/- SE) that was continued to exhaustion with a group average time of 26.8 +/- 5.8 min. Despite no significant change in MAP during exercise, MCA V(mean) decreased from 70.2 +/- 3.6 to 57.4 +/- 5.4 cm/s, Sv(O(2)) decreased from 68 +/- 1 to 58 +/- 2% at exhaustion, and both correlated to Pa(CO(2)) (5.5 +/- 0.2 to 3.9 +/- 0.2 kPa; r = 0.47; P = 0.04 and r = 0.74; P < 0.001, respectively). An effect on brain metabolism was indicated by a decrease in the cerebral metabolic ratio of O(2) to [glucose + one-half lactate] from 5.6 to 3.8 (P < 0.05). At the same time, the normalized low-frequency gain between MAP and MCA V(mean) was increased (P < 0.05), whereas the phase shift tended to decrease. These findings suggest that dynamic cerebral autoregulation was impaired by exhaustive exercise despite a hyperventilation-induced reduction in Pa(CO(2)).     

Influence of cold exposure on blood lactate response during incremental exercise

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electromyogram as an indicator of neuromuscular fatigue during incremental exercise

This study analysed the changes in the electromyographic activity (EMG) of the vastus lateralis muscle (VL) during an incremental maximal oxygen uptake test on a treadmill. A breakpoint in the integrated electromyogram (iEMG)-velocity relationship has already been interpreted in two ways: either as a sign of neuromuscular fatigue or as an expression of the iEMG-velocity relationship characteristics. The aim of this study was to test a method of distinguishing fatigue effects from those due to increases in exercise power. Eight well-trained male runners took part in the study. They completed a running protocol consisting of 4-min stages of increments in power output. Between each stage (about 15 s after the start of a minute at rest), the subjects had to maintain a standard effort: a 10-s isometric leg extension contraction [50% isometric maximal voluntary contraction (IMVC)]. The EMG was recorded during the running and isometric protocols, a change in the EMG signal during the isometric exercise being considered as the sign of fatigue. The iEMG-velocity relationships were strongly fitted by a second-order polynomial function for data taken at both the start (r = 0.98) and the end (r = 0.98) of the stage. Based on the stability of the 50%IMVC-iEMG relationship noted between stages, the start-iEMG has been identified as expressing the iEMG-velocity relationship without fatigue. The stage after which end-iEMG increased significantly more steeply than start-iEMG was considered as the iEMG threshold and was simultaneous with the ventilatory equivalent for carbon dioxide threshold. The parallel changes of minute ventilation and iEMG would suggest the existence of common regulation stimuli linked either to effort intensity and/or to metabolic conditions. The fall in intracellular [K⁺] has been discussed as being one of the main factors in regulating ventilation. Accepted: 16 December 1997     

Skeletal muscle oxygenation during incremental exercise

The purpose of this study was to investigate the relationship between muscle oxygenation level at exhaustion and maximal oxygen uptake (VO2max) in an incremental cycling exercise. Nine male subjects took part in an incremental exhaustive cycling exercise, and then cuff occlusion was performed. Changes in oxy-(deltaHbO2) and deoxy-(deltaHb) hemoglobin concentrations in the vastus lateralis muscle were measured with a near infrared spectroscopy (NIRS). Muscle oxygenation during incremental exercise was expressed as a percentage (%Moxy) of the maximal range observed during an arterial occlusion as the lower reference point. A systematic decrease was observed in %Moxy with increasing intensity. A significant relationship was observed between %Moxy at exhaustion and VO2max (p < 0.01). We concluded that the one of the limiting factor of VO2max is the muscle oxygen diffusion capacity, and %Moxy during exercise could be one of the indexes of muscle oxygen diffusion capacity.     

Nitric oxide and immune response

Nitric oxide (NO), initially described as a physiological mediator of endothelial cell relaxation plays an important role in hypotension. It is an intercellular messenger and has been recognized as one of the most versatile players in the immune system. Cells of the innate immune system--macrophages, neutrophils and natural killer (NK) cells use pattern recognition receptors to recognize molecular patterns associated with pathogens. Activated macrophages then inhibit pathogen replication by releasing a variety of effector molecules, including NO. In addition to macrophages, a large number of other immune system cells produce and respond to NO. Thus, NO is important as a toxic defense molecule against infectious organisms. It also regulates the functional activity, growth and death of many immune and inflammatory cell types including macrophages, T lymphocytes, antigen-presenting cells, mast cells, neutrophils and NK cells. However, the role of NO in non-specific and specific immunity in vivo and in immunologically mediated diseases and inflammation is poorly understood. This review discusses the role of NO in immune response and inflammation and its mechanisms of action in these processes.     

Plasma glucagon and catecholamines during exhaustive short-term exercise

Plasma glucagon and catecholamine levels were measured in male athletes before and after exhaustive 15 min continuous running and strenuous intermittent short-term exercise (3 X 300 m). Blood lactate levels were higher after the intermittent exercise (mean 16.7 mmol X 1(-1)) than after the continuous running (mean 7.1 mmol X 1(-1)). Plasma glucagon concentration increased during continuous running and intermittent exercise by 41% and 55%, respectively, and the increases in plasma noradrenaline concentration were 7.7- and 9.1-fold compared with the respective pre-exercise values. Immediately after the exercises plasma cyclic AMP, blood glucose and alanine levels were elevated significantly. The data suggest that the sympathoadrenal system is of major importance for liver glucose production during high-intensity exercises. Catecholamines directly stimulate liver glucose production and may indirectly stimulate it by enhancing the secretion of glucagon.     

Serum enzyme variations in men during an exhaustive "square-wave" endurance exercise test

The present study was designed to test if both the intensity and duration of the 45-min Square-Wave Endurance Exercise Test (SWEET) would produce changes in serum enzyme activities. Nine men, four sedentary (S) and five athletes (A), performed VO2 max and SWEET, at their Maximal Intensity of Endurance (MIE45) as defined by maximal heart rate and the impossibility of maintaining MIE 45 + 5% for 45 min. Arterial blood was sampled at rest (R), exercise (Ex) (45th min) and during recovery (15th min) for measurements of levels of Haemoglobin (Hb), Haematocrit (Hct), pH and seven serum enzymes: Creatine kinase (CPK), Hexose-phosphate isomerase (PHI), Aldolase (ALD), Lactate dehydrogenase (LDH), Malate dehydrogenase (MDH), Aspartate amino-transferase (ASAT or GOT), and Alanine aminotransferase (ALAT or GPT). Five enzymes increased significantly during exercise (MIE45), the delta % (Ex - R/R) increases were as follows: PHI (72%), MDH (28%), LDH (21%), CPK (17%), and GOT (13.5%), whilst only a 10% increase was observed for Hct and Hb and there was no significant change in the arterial pH. There was no correlation between the delta % of Hb, Hct, pH, and the results for the enzymes. Thus, it does not seem that haemoconcentration and arterial blood acidosis which occur during exercise are only at the origin of the observed increases in enzymes. A difference between "sedentary" and "athletes" subjects was found at rest and exercise (delta % = A - S/S) for CPK (R = 222%; Ex = 235%), GOT (R = 90%; Ex = 75%) and ALD (R = 99%; Ex = 54%). These results suggest that the MIE45, by measured increases in enzymatic activity, seems to require great muscular effort.     

Effects of aging and training status on ventilatory response during incremental cycling exercise

The aim of this study was to examine the effect of aging and training status on ventilatory response during incremental cycling exercise. Eight young (24 ± 5 years) and 8 older (64 ± 3 years) competitive cyclists together with 8 young (27 ± 4 years) and 8 older (63 ± 2 years) untrained individuals underwent a continuous incremental cycling test to exhaustion to determine ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (VO?max). In addition, the isocapnic buffering (IB) phase was calculated together with the hypocapnic hyperventilation. Ventilatory threshold occurred at similar relative exercise intensities in all groups, whereas RCP was recorded at higher intensities in young and older cyclists compared to the untrained subjects. The IB phase, reported as the difference between VT and RCP and expressed either in absolute (ml·min?1·kg?1 VO?) or in relative terms, was greater (p < 0.01) in both young and older trained cyclists than in untrained subjects, who were also characterized by a lower exercise capacity. Isocapnic buffering was particularly small in the older untrained volunteers. Although young untrained and older trained subjects had a similar level of VO?max, older athletes exhibited a larger IB. In addition, a higher absolute but similar relative IB was observed in young vs. older cyclists, despite a higher VO?max in the former. In conclusion, the present study shows that aging is associated with a reduction of the IB phase recorded during an incremental exercise test. Moreover, endurance training induces adaptations that result in an enlargement of the IB phase independent of age. This information can be used for the characterization and monitoring of the physiological adaptations induced by endurance training.     

Change in double product during stepwise incremental exercise

The purpose of this study was to observe the change in double product with increases in the intensity of bicycle exercise. Eleven young male adults participated in this study. The subjects performed graded bicycling exercise increasing 20 watts every 2 min from 0 watts until the heart rate (HR) reached 170 beats.min(-1). During exercise systolic blood pressure (SBP) and HR were continuously measured. Initially SBP gradually increased with the increase in workload, but when the intensity of exercise became even higher, the rate of increase slowed. On the other hand, the increase in HR was very small during the initial 5 min of exercise and when the intensity of exercise increased, the rate of increase of HR became higher. The polygonal regression analyses on the relation of double product to elapsed time revealed clear break-points. On average, the break-point of double product was 6.6 min (56 watts). These results clearly showed that the break-point of double product with an increase in workload appeared even though the workload was relatively low.     

Nitric oxide and changes of iron metabolism in exercise

Accumulated data imply that exercise itself might not lead to a true iron deficiency or 'sport anaemia' in a healthy athlete who has adequate iron intake. The higher prevalence of iron deficiency anaemia in younger female athletes might be not due to exercise itself, but probably results from dietary choices, inadequate iron intake and menstruation. These factors can also induce iron deficiency or anaemia in the general population. However, exercise does affect iron metabolism, leading to low or sub-optimal iron status. The underlying mechanism is unknown. In this review, recent advances in the study of the effect of exercise on iron metabolism and nitric oxide, and the relationship between nitric oxide and iron status in exercise are discussed. A hypothesis that increased production of nitric oxide might contribute to sub-optimal iron status in exercise is proposed.     

Breathing pattern in highly competitive cyclists during incremental exercise

The purpose of our investigation was to analyse the breathing patterns of professional cyclists during incremental exercise from submaximal to maximal intensities. A group of 11 elite amateur male road cyclists [E, mean age 23 (SD 2) years, peak oxygen uptake (VO2peak) 73.8 (SD 5.0) ml kg(-1) min(-1)] and 14 professional male road cyclists [P, mean age 26 (SD 2) years, (VO2peak) 73.2 (SD 6.6) ml kg(-1) min(-1)] participated in this study. Each of the subjects performed an exercise test on a cycle ergometer following a ramp protocol (exercise intensity increases of 25 W x min(-1)) until the subject was exhausted. For each subject, the following parameters were recorded during the tests: oxygen consumption (VO2), carbon dioxide output (VCO2), pulmonary ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen (VE x VO2(-1)) and carbon dioxide (VE x VCO2(-1)), end-tidal partial pressure of oxygen and partial pressure of carbon dioxide, inspiratory (tI) and expiratory (tE) times, inspiratory duty cycle (tI/tTOT, where tTOT is the time for one respiratory cycle), and mean inspiratory flow rate (VT/tI). Mean values of VE were significantly higher in E at 300, 350 and 400 W (P < 0.05, P < 0.05 and P < 0.01, respectively); fb was also higher in E in most moderate-to-maximal intensities. On the other hand, VT showed a different pattern in both groups at near-to maximal intensities, since no plateau was observed in P. The response of tI and tE was also different. Finally, VT/tI and tI/tTOT showed a similar response in both P and E. It was concluded that the breathing pattern of the two groups differed mainly in two aspects: in the professional cyclists, VE increased at any exercise intensity as a result of increases in both VT and fb, with no evidence of tachypnoeic shift, and tE was prolonged in this group at high exercise intensities. In contrast, neither the central drive nor the timing component of respiration seem to have been significantly altered by the training demands of professional cycling.     

Nigrostriatal dopaminergic activity is increased during exhaustive exercise stress in rats

Exercise capacity is influenced by both increases and decreases in central dopaminergic activity. To investigate the effects of exercise stress on intracerebral dopamine metabolism, rats were run on a motor driven treadmill at 37 m/min for varying times up to exhaustion at 19.6 +/- 0.6 min. Dopamine, DOPAC, and HVA concentrations in striatum, brain stem, and hypothalamus increased towards exhaustion. 5-HIAA concentrations increased in striatum whereas norepinephrine concentrations decreased in hypothalamus. The results indicate that delayed increases in dopaminergic activity occurs during exercise. These, and other observations indicate that central dopaminergic activity modulates exercise performance.