bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exercise catecholamine concentrations inhibit acetylcholine release in airways
Authors: ROBINSON N. E. , ZHANG X‐Y. , LEBLANC P. H. , DERKSEN F. J. 
Published: June 2010

SummaryWe determined the effects of exercise induced concentrations of epinephrine (E) and norepinephrine (NE) on acetylcholine (ACh) release and smooth muscle contraction. To determine ACh release, trachealis strip bundles were suspended in 2 ml tissue baths in the presence of neostigmine (10−6M), guanethidine (10−5M) and atropine (10−7M), and stimulated by electrical field stimulation (EFS; 20V, 0.5 ms, 0.5 Hz, for 15 min). EFS‐induced ACh release was measured by high‐performance liquid chromatography coupled with electrochemical detection. Concentration responses to E and NE (10−8to 10−5M) were determined. In time‐control tissues, ACh release averaged 8.2 ± 0.9 pmol/g/min. Epinephrine caused significant inhibition of ACh release at concentrations of 10−7M or greater and NE at 10−6M or greater. E‐ and NE‐induced inhibition of ACh release was attenuated by the α2‐adrenoceptor antagonist idazoxan (10−6M) but not by the α2‐antagonist prazosin (10−6M) nor the β‐antagonist propranolol (10−6M). We determined if E and NE had inhibitory actions on smooth muscle by examining their effect on the ACh concentration‐response curve of trachealis. E (10−6M) inhibited contraction only at 10−7M ACh, i.e. when muscle tension was low. NE had no effect. Exercise induced concentrations of E inhibit cholinergically mediated bronchospasm primarily by α2‐mediated prejunctional inhibition of ACh release and, to a lesser degree, by a post junctional effect on airway smooth muscle. NE only inhibits ACh release but not significantly at the concentrations achieved during exercise.
Assessment of diaphragm strength and activation by transvenous phrenic nerve stimulation
Authors: DESMECHT D. , LINDEN A. , LEKEUX P. 
Published: June 2010

SummaryThe purpose of the present work is to report the feasibility, humaneness and reliability of a method for measurement of diaphragm performance in intact, awake horses. Phrenic nerves were activated through thevena cavaby repeated transvenous stimulations (40 to 80V, 100 to 200 μs square‐wave pulses), using an electrode‐catheter advanced from the jugular vein. Twitches were produced that caused changes in gastric and oesophageal pressures, abdominal and rib cage motion and airflow tracings, suggesting that the diaphragm was activated. Four sites were selected over each hemithorax for placement of surface electrodes able to detect and to ensure constancy of evoked compound diaphragmatic action potentials (CDAP). Trains of repeated pulses applied to nerves (10 to 100 Hz) gave repeatable diaphragmatic force‐frequency relationships. Nerve stimulation produced no visible signs of discomfort and increases in Cortisol and β‐endorphins similar to those produced by nasogastric intubation. Transvenous single and repeated activations of the phrenic nerves in ponies is feasible, free of iatrogenic risks and ethically acceptable, recording reliable evoked potentials via surface electrodes is possible, and force‐frequency characteristics of the diaphragm can be conveniently obtained from simultaneous oesophageal and gastric pressures measurements.
Effect of gas collection system on respiratory and stride frequency and stride length
Authors: GEOR R. J. , STAEMPFLI H. R. , MCCUTCHEON LAURA J. , PRINGLE J. , YOUNG S. 
Published: June 2010

SummaryThe objective of this study was to determine the effects of 2 different gas collection systems on locomotor and ventilatory responses to exercise in a group of 8 Standardbred pacers. Each horse completed the same incremental treadmill exercise test (8, 9, 10 and 11 m/s on a 3° incline) using an open (flow‐through) system (OS) and a closed system (CS) incorporating one way valves. Only 2 horses completed the final (11 m/s) step using the CS. Peak values for V̇O2, O2pulse, plasma lactate and respiratory exchange ratio (RER) were significantly higher for the OS compared with the CS. There was no change in breathing frequency (Vf) or stride frequency (Sf) (mean ± s.e. 128 ± 2 strides/min) throughout either exercise test, however Vfwas significantly lower when horses exercised in the CS (68 ± 6 breaths/min) when compared to the OS (100 ± 3 breaths/min). There was a linear increase in stride length (SL) with speed (3.8 ± 0.1 m/stride at 8 m/s to 5.0 ± 0.2 m at 11 m/s) but no difference in SLbetween systems. There was also a linear increase in VTmeasured in the CS. Incremental exercise did not alter the Sf:Vfratio, however Sf:Vfwas significantly lower in the OS (1.3:1) when compared to the CS (2.1:1). There was a significant difference between systems for PaO2and PaCO2values at all increments of exercise. The lower Vfmeasured in the CS was associated with marked hypercapnia (59 ± 7 mmHg at 10 m/s) and hypoxaemia (45 ± 3 mmHg at 10 m/s). The higher Vfmeasured in the OS was associated with hypocapnia (35 ± 2 mmHg) at 8 m/s. It was concluded that although Vfvaried between OS and CS, Vfand Sfdid not change during incremental exercise with either system. Therefore the increase in speed was achieved solely by an increase in SL. Although the CS did not alter locomotor parameters or V̇O2at lower increments of exercise, the altered Vfappeared to limit work capacity.
Neuroendocrine control of blood volume, blood pressure and cardiovascular function in horses
Authors: McKEEVER K. H. , HINCHCLIFF K. W. 
Published: June 2010

SummarySeveral body systems make critical contributions to the defence of blood volume, mean arterial pressure and plasma tonicity. These mechanisms ensure adequate blood flow to the working muscles and vital tissues along with the provision of adequate fluid volume for sweating and thermoregulation. The present paper integrates data from several recent studies that examined the neuroendocrine control of cardiovascular function in exercising horses. These studies focused on the effects of exercise on plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin activity (PRA) and aldosterone (ALDO), hormones associated with the regulation of blood pressure, the distribution of blood flow and the long term control of vascular fluid volume. Data were collected during incremental and endurance exercise, following frusemide administration and after splenectomy. Increases in ANP during exercise were associated with increased atrial pressure and stretching of the atrium. Increases in PRA and ALDO are correlated with increases in sympathetic activity during incremental exercise and with decreases in plasma Na+and CI−concentrations. Plasma AVP increases later in exercise in response to fluid losses, increases in plasma osmolality, and decreases in right atrial pressure. AVP has a minimal effect on renal function during exercise and may be more important during recovery, when it stimulates thirst and drinking. Frusemide and splenectomy decrease atrial pressure, resulting in lower plasma ANP and greater plasma AVP concentrations during steady‐state submaximal exercise. The ANP and AVP responses are part of the neuroendocrine action of the cardiopulmonary baroreflex which appears to mediate the accommodation of the mobilised splenic reserve in the horse. In summary, exercise induced increases in ANP, AVP, PRA and ALDO in the horse appear to play an important role in cardiovascular homeostasis.
Maximum oxygen transport and utilisation before and after splenectomy
Authors: WAGNEFT P. , ERICKSON B. K. , KUBO K. , HIRAGA A. , KAI M. , YAMAYA Y. , RICHARDSON R. , SEAMAN JULIE 
Published: June 2010

SummaryA major factor contributing to the athletic ability of the horse is exercise induced splenic contraction that augments both circulating blood volume (by about 12 litres) and haemoglobin concentration [Hb] (by a factor of 1.5–2). We examined separately the consequences of 1) splenectomy and 2) subsequent transfusion of blood at the lower post splenectomy [Hb] on pulmonary and muscle O2transport and pulmonary haemodynamics, to elucidate the separate influences of blood volume and [Hb] augmentation on these processes. We studied 6 Thoroughbreds (bwt 472 kg), (3 splenectomised, 3 controls). Splenectomy reduced V̇O2maxby 31 ± 3% (s.e.); transfusion of 11.7 litres whole blood at 42% haematocrit restored V̇O2maxto 94 ± 7% of original values. Splenectomy reduced maximal cardiac output by 15 ± 6%; transfusion increased it to 106 ± 10% of pre‐splenectomy values. The combination of splenectomy and transfusion reduced PaCO2by 14 ± 0.5 Torr, increased PaO2by 17 ± 0.4 Torr and arterial saturation by 5 ± 3% at V̇O2max. Splenectomy reduced maximal pulmonary artery pressure from 90.4 ± 1.4 to 42.4 ± 4.8 Torr; transfusion partially restored this to 71.5 ± 5.5 mmHg, despite the lower haematocrit. Splenectomy reduced muscle O2diffusional conductance (DO2) in direct proportion to the reduced maximal [Hb] while transfusion only slightly increased DO2. On the other hand, DO2was poorly related to changes in cardiac output.Although based on a small number of horses, this study suggests that 1) increased [Hb] from splenic contraction is not essential for achieving V̇O2max; a normal circulating blood volume at a moderate [Hb] is sufficient, 2) [Hb] plays an important role in overall muscle O2diffusional conductance and also affects pulmonary artery pressure and 3) splenectomy produced substantial hyperventilation (in relation to V̇O2), permitting eucapnia and increased arterial oxygenation at V̇O2max. This was still observed after transfusion despite restoration of exercise capacity and V̇O2max.
Regional differences in pulmonary artery endothelial function: a role in the site of EIPH?
Authors: PELLETIER N. , ROBINSON N. E. , KAISER L. , DERKSEN F. J. 
Published: June 2010

SummaryExercise induced pulmonary haemorrhage (EIPH) is thought to result from capillary stress failure associated with high pulmonary vascular pressures during heavy exercise. One possible mechanism for the caudodorsal distribution of haemorrhage is preferential distribution of blood flow to affected regions due to regional differences in pulmonary vascular regulation. Endothelial cells (EC) are known controllers of vascular smooth muscle tone and could play a role in regional distribution of blood flow. The present study investigated relaxation responses to the endothelium‐dependent and independent vasodilators, methacholine (MCh) and nitroglycerin (NTG) in pulmonary arteries from the caudodorsal (top) and cranioventral (bottom) regions of the lung. Pulmonary arteries (7 mm diameter) from 6 horses were isolated from top and bottom regions of the lung and vessels with and without endothelium were mounted in 15 ml tissue baths. Vessels were pre‐contracted with norepinephrine (10−6M) and changes in isometric tension in response to MCh (10−6M) and NTG (10−6M) were compared. MCh consistently relaxed, and never contracted, endothelium‐intact top vessels. In top vessels, relaxation was abolished by removal of EC, suggesting an obligatory role of EC in MCh relaxation. However, in bottom vessels, a small transient relaxation was followed by a profound contraction, enhanced by EC removal. Relaxation to NTG was similar in all vessels. Therefore, in response to MCh, top vessels relax in an endothelium‐dependent manner, while bottom vessels contract. Similar regional differences in endothelium dependent flow mediated vasodilation may result in higher blood flow to the caudodorsal regions of the lung and hence be responsible in part for the location of EIPH.
Reproducibility of a standardised exercise test for Standardbred trotters under field conditions
Authors: DUBREUCQ C. , CHATARD J.C. , COUROUCE A. , AUVINET B. 
Published: June 2010

SummaryThe reproducibility of a standardised exercise test was evaluated in 2 conditions with 2 groups of Standardbred horses: 1) the first condition was a test and a re‐test performed with a 1 week interval by 11 trotters on their usual training track (2) the second condition was a test and a re‐test performed with another group of 8 horses on 2 different tracks with a 9 day interval, in order to assess the influence of changing the place of the test. The test was composed of 3 steps, conducted at an increasing speed. The duration of each step was 3 min with a 1 min rest between 2 steps at a walking pace. The speed level used for each step depended on the age and fitness of the horses. Mathematic treatment of the collected data, speed, heart rate and venous blood lactate measured after each step, allowed the estimation of 5 fitness parameters: V200, V4, V2, HR2and HR4. The Spearman rank correlation coefficients calculated for these indicators between the 2 tests measured during the experiment (1) and the experiment (2) were higher than 0.79 (P < 0.05) for V200, V4, V2and HR2.The standardised exercise test proposed in the present work, was demonstrated to be reliable in field conditions for Standardbred horses.
Selected echocardiographic parameters and right sided pressures of the mule
Authors: TUCKER R. L. , WICKLER S. J. , LONDON C. , WYLE A. , GABBARD M. 
Published: June 2010

SummaryAlthough there are references to mules having an innate ability to withstand higher work loads than horses, there are relatively few physiological studies that substantiate these statements. The purpose of this study was to establish baseline information on cardiac dimensions and right sided pressures of the normal mule using echocardiography and cardiac catheterisation. Selected cardiac dimensions of 10 adult non‐sedated mules were measured with 2‐D real time and M‐mode echocardiography. This was followed by catheterisation of the pulmonary artery, right ventricle and right atrium for measurement of pressures. End‐diastolic left ventricular lumen diameter, interventricular septum thickness, left ventricular free wall thickness and aortic root diameter measured mean ± s.d. 11.1 ± 1.5 cm, 2.8 ± 0.3 cm, 3.3 ± 0.3 cm and 7.0 ± 0.9 cm, respectively and the end‐systolic diameter for the left ventricular lumen measured 6.7 ± 1.3 cm yielding a fractional shortening of mean ± s.d. 40.4 ± 5.7%. Right atrial mean pressure, right ventricular peak systolic pressure and pulmonary arterial mean ± s.d. pressure measured 6.28 ± 1.6 mmHg, 55.3 ± 7.3 mmHg and 31.4 ± 5.4 mmHg, respectively. Although data collected from this study were limited to 10 normal animals, no significant difference in cardiac dimensions or right sided pressures were found compared to reported values in horses of similar size.
Sensory nerve fibres and receptors in equine distal forelimbs and their potential roles in locomotion
Authors: BOWKER R. M. , LINDER K. , SONEA I. M. , GUIDA L. A. 
Published: June 2010

SummarySensory innervation of the equine distal forelimb was examined using several different anatomical techniques with each revealing a different morphological component of the sensory apparatus in the foot. Electron microscopic examination of the medial palmar nerve (N.digitalis communis II) revealed predominantly unmyelinated nerve fibres with a ratio of unmyelinated/ myelinated nerves at the level of the metacarpophalangeal joint of 3.67:1. Sensory peptides (substance P, neurokinin A, calcitonin gene‐related peptide and peptide histidine isoleucine) were observed immunocytochemically to innervate much of the equine foot, including the dermis of the dorsal wall and sole, the suspensory ligaments (ligamenta sesamoidea collateralia) (CSL) and the distal sesamoidean impar ligament (ligamentum sesamoideum distale impar), the synovial cavities and bones. These sensory peptides were usually associated with the adventia of the arterial vessels rather than the muscularis layer in contrast to neuropeptide Y. None or only scant immunoreactivity was present in the venules and capillary beds. Lamellated corpuscles in the loose connective tissues proximal to CSL appeared to be innervated by myelinated nerves. These different morphological components of sensory nerves innervating the equine digit suggest that these nerves are functionally complex in that during neurotransmission they have effects both within the spinal cord and within the peripheral tissues.
Electromyographic activity of the hindlimb muscles during the walk, trot and canter
Authors: TOKURIKI M. , AOKI O. 
Published: June 2010

SummaryThetensor fasciae lataeand the middle part of thebiceps femoriswere investigated electromyographically and kinematically in 4 Thoroughbred horses with or without a rider during the walk, trot and canter. EMG activity of thetensor fasciae lataebegan in the middle of the stance phase and ceased in the early period of the swing phase during the walk and trot in horses with or without a rider. During the canter, the onset and termination of muscle activity began earlier than during symmetrical locomotion. Its EMG activity had a higher amplitude during the stance phase than during the swing phase. These results indicate that thetensor fasciae lataemay act as an extensor or stabiliser of the stifle joint during locomotion. During the walk, EMG activity of the middle part of thebiceps femoriswas silent or weak. During the trot and canter, the muscle had a high amplitude of EMG activity and was active from the middle of the swing phase to the early or middle period of the stance phase in horses with or without a rider. This part of the muscle may work as an extensor of the hip joint during locomotion.
Temporal stride patterns in horses with experimentally induced fore‐ or hindlimb lameness
Authors: BUCHNEFP H. H. F. , SAVELBERG H. H. C. M. , SCHAMHARDT H. C. , BARNEVELD A. 
Published: June 2010

SummaryIn a kinematic study of equine lameness, temporal stride variables were investigated for their significance as diagnostic indicators and as a means of compensation for lameness. Kinematics of 11 clinically sound Dutch Warmblood horses were recorded while walking (1.6 m/s) and trotting (3.5 m/s) on a treadmill. A transient lameness model, provoking pain on the hoof sole, was used to induce 3degreesof fore‐ and hindlimb lameness. Intra‐ and interlimb stride variables as well as left‐to‐right symmetry were analysed using a 2 way analysis of variance (significance level: P<0.05). At the walk, stride duration was not affected by fore‐ or hindlimb lameness, while intra‐ and interlimb timing showed minor changes. At the trot, the stride duration in forelimb lameness decreased by 3.1% and relative stance duration of all limbs became longer (5.3% in forelimbs, 1.5% and 3.2% in hindlimbs). The diagonal advanced placement of the forelimbs increased and the duration of the suspension phase following the lame diagonal decreased by 61%. Left‐to‐right symmetry decreased for the suspension phase and contralateral advanced placement, while the stance durations remained symmetrical. In hindlimb lameness the stride duration at the trot decreased by 3.7% and the stance duration of the sound hind limb increased by 2.7%. Diagonal advanced placement, suspension phase and symmetry variables remained unaffected. It was concluded that compensation for lameness by changing temporal stride patterns is more pronounced in fore than in hindlimb lameness. The maintenance of symmetry in most stride variables in mild lamenesses limits their value as lameness indicators.
Kinematic analysis of successful and unsuccessful attempts to clear a water jump
Authors: CLAYTON HILARY M. , COLBORNE G. ROBERT , BURNS THERESA E. 
Published: June 2010

SummaryVideo recordings (60 Hz) of horses jumping a 4.5 m wide water jump were made during the team show jumping competition at the 1992 Olympic Games. The tapes were digitised and the results were analysed using the Ariel Performance Analysis System software and Statistical Packages for the Social Sciences. Eighteen horses were studied: 12 that cleared the water jump (Group 1) and 6 that failed to clear the width of the jump (Group 2). Four variables that influence the horizontal distance jumped were measured: horizontal velocity, vertical velocity, height of the centre of gravity (CG) at lift off and height of the CG at landing. The angle of projection was computed from the horizontal and vertical velocities. The angle of projection (Group 1: 15.2° ± 2.2°,Group 2: 12.2° ± 1.8°, F=0.010) and the vertical velocity of the CG (Group 1: 2.03 ± 0.22 m/s,Group 2: 1.56 ± 0.24 m/s, F=0.001) were significantly different between the 2 groups. There were no differences in the height of the CG at lift off (Group 1: 1.36 ± 0.08 m,Group 2: 1.40 ± 0.05 m), the height of the CG at landing (Group 1: 1.35 ± 0.12 m,Group 2: 1.30 ± 0.11 m) or the horizontal velocity of the CG (Group 1: 7.59 ± 0.60 m/s,Group 2: 7.48 ± 0.11 m/s). It was concluded that, to be a successful water jumper, the horse must generate a large vertical velocity during the take off.
Relative increase in areas of muscle fibre types in horses during growth
Authors: GUNN H. M. 
Published: June 2010

SummaryThe relative growth of muscle fibre types as distinguished by the myosin ATPase reaction at pH 9.5 in m. semitendinosus, m. diaphragma and m. pectoralis transversus of growing Thoroughbreds and other horses ranging in age from perinatal life to adulthood was investigated.The growth rate of the area of myosin ATPase high‐reacting fibres in m. semitendinosus of both types of horse and in m. pectoralis transversus of Thoroughbreds was greater than that of low reacting fibres. Myosin ATPase low reacting fibres increased in area faster than high reacting fibres in the diaphragm of both types of horse and m. pectoralis transversus of other horses. These differential growth rates result in myosin ATPase high reacting fibres being larger than myosin ATPase low reacting fibres in m. semitendinosus and m. pectoralis transversus in adults of both types however, low‐reacting fibres are larger than high reacting fibres in m. diaphragma of adults of both types. These results suggest that the greater relative muscle mass of the proximal limbs of Thoroughbreds and associated greater mean fibre area associated are with relatively faster growing high reacting fibres in their muscles than those of other horses.
Slow myosin heavy chain content of muscles measured by ELISA
Authors: VALETTE J. P. , BARREY E. , JOUGLIN MAGGY 
Published: June 2010

SummaryEquine type I muscle fibres were characterised in 14 muscles by enzyme‐linked immunosorbent assay (ELISA) with a monoclonal antibody specific for slow myosin heavy chains (MHC I). Slices of vastus lateralis, rectus femoris, biceps femoris, semitendinosus, semimembranosus, gluteus medius, gluteus superficialis, cutaneus trunci, masseter, triceps brachii, biceps brachii, deüoideus and diaphragm were obtained from a one‐year‐old Standardbred. For each muscle, 4 samples per slices were excised at different sites and 2 contiguous sub‐samples were immediately frozen in liquid nitrogen and stored at –80 °C until analysed. Muscle proteins were specifically extracted and analysed by ELISA. The MHC I content varied widely in the different muscles from cutaneus trunci (9%) to masseter (69%). A 3‐way analysis of variance showed that the MHC I content was different between muscles (P < 0.001) and within the sites studied (P < 0.01). The 2 contiguous sub‐samples were not different from each other (P > 0.05). It is concluded that the ELISA method allowed the accurate measurement of a wide range of MHC I in equine muscles. This technique is less time consuming than histological techniques and offers new applications for muscle fibre typing.