Omneity® Pellets
All-In-One Vitamin & Mineral Pellet
Topic:Blood Vessels
Blood vessels in horses are integral components of the circulatory system, responsible for the transportation of blood throughout the body. They consist of arteries, veins, and capillaries, each serving distinct functions in maintaining circulatory efficiency. Arteries carry oxygen-rich blood away from the heart to various tissues, while veins return deoxygenated blood back to the heart. Capillaries facilitate the exchange of nutrients, gases, and waste products between blood and tissues. The structure and function of equine blood vessels are subjects of study due to their role in health and disease, including conditions such as laminitis and equine metabolic syndrome. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, and pathophysiology of blood vessels in horses.
Horse trophoblasts produce tumor necrosis factor alpha but not interleukin 2, interleukin 4, or interferon gamma. The distribution of four cytokines was analyzed in the endometrium and trophoblast of the horse between Days 30 and 55 of gestation. Endometrial tissues, invasive trophoblast (chorionic girdle), and noninvasive trophoblast (chorion and allantochorion) were examined separately. Cytokine expression was determined by amplification of specific mRNA via the reverse transcriptase polymerase chain reaction (RT-PCR). Messenger RNA for interleukin 2 (IL-2), interleukin 4 (IL-4), and interferon gamma (IFN gamma) was detected in endometrial tissues, unstimulated peripheral blood lymphocytes, and control ...
Stress failure of pulmonary capillaries as a limiting factor for maximal exercise. The pulmonary blood-gas barrier has a basic physiological dilemma. On the one hand it needs to be extremely thin for efficient gas exchange. On the other hand it also needs to be immensely strong because the stresses on the pulmonary capillary wall become extremely high when the capillary pressure rises on exercise. Maximal hydrostatic pressures in human pulmonary capillaries during exercise are not accurately known but must exceed 30 mmHg. In some animals, for example thoroughbred horses, the capillary pressure rises to about 100 mmHg. These pressures cause stresses in the capillary wall of 5...
Endothelial lipopigment as an indicator of alpha-tocopherol deficiency in two equine neurodegenerative diseases. Two spontaneous neurodegenerative diseases of the horse, equine motor neuron disease (EMND) and equine degenerative myeloencephalopathy (EDM), have been associated with alpha-tocopherol deficiency, and both were characterized by prominent accumulations of endothelial lipopigment in the small vessels of the spinal cord. These endothelial pigment deposits appear to be reversible. In EMND horses pasture-supplemented for 9 months or more after the progression of weakness and wasting had arrested, there was very little endothelial lipopigment. The origin and the potential effects of these endotheli...
Stress failure of pulmonary capillaries as a mechanism for exercise induced pulmonary haemorrhage in the horse. Exercise induced pulmonary haemorrhage (EIPH) is a serious problem in the Thoroughbred industry. The condition apparently occurs essentially in all Thoroughbreds in training but the mechanism has proved elusive. There is now strong evidence that the condition is caused by mechanical failure of the walls of the pulmonary capillaries when the pressure inside them rises to very high levels. It is well known that pulmonary capillaries have extremely thin walls to allow rapid exchange of respiratory gases across them. Recently we have shown that the wall stresses are very large when the capillary t...
Pulmonary vascular pressures of thoroughbreds increase rapidly and to a higher level with rapid onset of high-intensity exercise than slow onset. Previous studies of pulmonary vascular pressures have utilised gradual incremental step exercise protocols, but in competitive racing at the track, horses perform rapid acceleration high-intensity exercise. The rate of rise in pulmonary vascular pressures under conditions of quick onset high-intensity exercise is unknown. Catheter mounted manometers, whose in vivo signals were matched with pressure signals obtained via transducers connected to fluid-filled lumens from same cardiovascular sites, were used to compare right heart and pulmonary vascular pressures in 8 healthy Thoroughbreds perform...
Atrial and ventricular myocardial blood flows in horses at rest and during exercise. Right atrial, pulmonary artery, pulmonary capillary, pulmonary artery wedge, and systemic blood pressures of strenuously exercising horses increase markedly. As a consequence, myocardial metabolic O2 demand in exercising horses must be high. Experiments were, therefore, carried out on 9 healthy, exercise-conditioned horses (2.5 to 8 years old; 481 +/- 16 kg) to ascertain the regional distribution of myocardial blood supply in the atria and ventricles at rest and during exercise. Blood flow was measured, using 15-micron-diameter radionuclide-labeled microspheres that were injected into the left...
Characterization of the hemodynamic and metabolic alterations in the large colon of horses during low-flow ischemia and reperfusion. Effects of low-flow ischemia and reperfusion of the large colon on systemic and colonic hemodynamic and metabolic variables were determined in horses. Twenty-four adult horses were randomly allocated to 3 groups: sham-operated (n = 6), 6 hours of ischemia (n = 9), and 3 hours of ischemia and 3 hours of reperfusion (n = 9). Low-flow ischemia was induced in groups 2 and 3 by reducing colonic arterial blood flow to 20% of baseline. Heart rate, arterial blood pressures, cardiac index, pulmonary artery pressure, right atrial pressure, and colonic blood flow were monitored. Arterial, mixed-venous, a...
The role of nitric oxide in the responses of equine digital veins to vasodilator and vasoconstrictor agents. Isolated equine digital veins were examined in vitro to study the importance of the endothelium in the responses to both vasodilator and vasoconstrictor agents and to characterise the endothelial-derived mediators involved. Carbachol (Cch; 1 microM) and bradykinin (Bk; 1 nM) caused relaxation of U44069-induced tone by 79.5 +/- 0.35% and 73.7 +/- 4.0% respectively. Mechanical removal of the endothelium completely prevented relaxant responses to Cch and to Bk showing they were mediated by the endothelium. Treatment of veins with NG-nitro-L-arginine methyl ester (L-NAME; 30 and 300 microM) inhibi...
Pulmonary vascular pressures of strenuously exercising thoroughbreds after administration of flunixin meglumine and furosemide. High-intensity exercise results in a dramatic increase in mean pulmonary capillary blood pressure of horses, and administration of furosemide 4 hours before exertion significantly attenuates this exercise-induced increment. To test whether this effect of furosemide is mediated via release of prostaglandins, right atrial and pulmonary vascular pressures were measured in 8 healthy, sound, exercise-trained Thoroughbreds at rest and during incremental-step exercise on a treadmill. Horses were studied on 3 separate occasions: after i.v. administration of saline (0.9% NaCl) solution, after administr...
Capillary blood transit time in muscles in relation to body size and aerobic capacity. The mean minimal transit time for blood in muscle capillaries (tc) was estimated in six species, spanning two orders of magnitude in body mass and aerobic capacity: horse, steer, dog, goat, fox and agouti. Arterial (CaO2) and mixed venous (CvO2) blood O2 concentrations, blood hemoglobin concentrations ([Hb]) and oxygen uptake rates were measured while the animals ran on a treadmill at a speed that elicited the maximal oxygen consumption rate (VO2max) from each animal. Blood flow to the muscles (Qm) was assumed to be 85% of cardiac output, which was calculated using the Fick relationship. Total...
Heterogeneity of pericyte populations in equine skeletal muscle and dermal microvessels: a quantitative study. The objective of this ultrastructural investigation was to determine if populations of pericytes in equine dermal and skeletal muscle capillaries increase in a head-to-foot direction, as has been reported in human skeletal muscles. Samples of equine microvessels were obtained from the longissimus dorsi skeletal muscle 150 cm. from the ground, from the dermis above this muscle, from the extensor carpi radiali muscle at 55 cm. from the ground, from the dermis adjacent to that muscle, and from dermis 15 cm. from the ground, just above the hoof wall. Tissues were processed for transmission electro...
Measurements of blood flow and xanthine oxidase activity during postischemic reperfusion of the large colon of ponies. To assess right colic artery blood flow and relevance of xanthine dehydrogenase/xanthine oxidase after experimentally induced strangulation obstruction and reperfusion of the colon, 5 ponies were subjected to 2.5 hours of complete ischemia of the left dorsal and ventral colons, allowed to recover from surgery, and monitored during a 48-hour reperfusion period. Five ponies were subjected to sham surgery and served as controls. All ponies had a Doppler ultrasound blood flow monitor implanted on the right colic artery near the pelvic flexure 10 to 14 days prior to the ischemic period. Colic arter...
The structure, innervation and location of arteriovenous anastomoses in the equine foot. In the foot of the horse, arteriovenous anastomoses (AVAs) of epithelioid type occurred in the dermis of the coronary band, in the coronary and terminal papillae, in neurovascular bundles and at the entrance to and along the length of the dermal laminae. A particular feature of the epithelioid segment of AVAs in the horse, compared with that of other species, was the height and surface complexity of many of the endothelial cells. They extended into the lumen, forming undercut and tunnel-like areas which correlated with the characteristic surface marking of AVAs observed in vascular casts. The ...
Comparative aspects of the strength of pulmonary capillaries in rabbit, dog, and horse. In previous studies of rabbit and dog lung, we demonstrated stress failure of pulmonary capillaries at high transmural pressures (Ptm). The Ptm necessary to elicit stress failure was 40 cmH2O higher in dog than rabbit, and the total blood-gas barrier (BGB) thickness was greater in dog than rabbit. This suggests that stress failure may be related to BGB thickness, and is consistent with the Laplace relationship which states that wall stress is proportional to capillary radius but inversely proportional to wall thickness. In the present studies, we compared BGB thickness and an index of capillar...
Hemorheologic alterations induced by incremental treadmill exercise in thoroughbreds. Hemorheologic alterations induced by incremental treadmill exercise were examined in 5 Thoroughbreds. Blood viscosity; PCV; RBC filterability, density gradient profile, and shape; serum and RBC electrolyte concentrations; and plasma total solids and lactate concentrations were measured before exercise, at treadmill speeds of 9 and 13 m/s, and 10 minutes after exercise. Exercise was associated with significant (P < 0.05) increases in PCV, blood viscosity, and plasma total solids concentration. After adjustment of PCV to 40% by adding or removing each horse's own plasma, blood viscosity ...
Microvascular thrombosis associated with onset of acute laminitis in ponies. The hypothesis that equine laminitis is caused by thrombosis of vessels in the laminar corium (dermis) was investigated. Hemostatic alterations were evaluated by determining platelet count, platelet survival, platelet adhesiveness to vascular subendothelium, activated clotting time, and whole blood recalcification time. Thrombosis of vessels in the hoof wall was evaluated by scintigraphic studies of the hoof wall after administration of indium-111 (111In)-labeled platelets, contrast arteriography, and histologic examination. Platelet count remained constant before and at the onset of lameness;...
Vascular perfusion in horses with chronic laminitis. Vascular perfusion casts were used to define and characterise the macroscopic perfusion defects present in the distal digit of 11 horses affected by chronic laminitis. Five clinically normal horses were used as controls. Based on clinical history and clinical status, horses with chronic laminitis were classified as being potentially treatable or clinically refractory. Eleven macroscopic vascular defects were noted in the casts from horses with laminitis. Four types of lesions were identified in the submural laminar circulation, 3 in the coronary bed and 4 were associated with the solar circula...
Evaluation of laser Doppler flowmetry for measuring coronary band and laminar microcirculatory blood flow in clinically normal horses. Once daily for 3 days, laser Doppler flowmetry was used in 5 healthy, nonsedated adult horses to evaluate coronary band and laminar microcirculatory blood flow (MBF) in both forelimbs. The coronary band had significantly (P < 0.05) higher MBF than did the laminae on the days evaluated. Significant variation in MBF was not found over the 3-day measurement period in any one site. Significant (P < 0.05) variation was found in coronary band MBF among horses. This variation was not observed in laminar MBF. On occlusion of the digital arteries at the level of the fetlock, marked decrease in co...
Effects of tumor necrosis factor on in vitro digital arterial responses in horses. Endotoxin given in vivo has been shown to inhibit endothelial dependent relaxation, and augment adrenergic (norepinephrine) contractions in isolated palmar digital arteries of horses. A study, using tumor necrosis factor (TNF) in vitro, was performed to determine the possible cause of these vascular alterations. Palmar digital arteries were surgically removed from 6 horses under general anesthesia, cut into 4-mm vascular rings (4 segments/horse), suspended in tissue baths, and attached to force displacement transducers for measurement of vascular tension. Four in vitro treatment groups were ev...
Jugular vein wall repair after intravenous injection in equids. The evolution of the healing process of venous puncture wounds was studied macroscopically and light-microscopically in order to determine the time of venipuncture. Seven small equids of various ages, all in normal healthy condition, were experimentally injected in the external jugular vein with a physiological Hartmann solution at different times before euthanasia. Two types of needle diameters i.e. 16.5 G and 19 G, were used. A fairly good uniformity in the healing process was seen in the 7 animals. In most cases the lesions induced within 5 weeks before death were macroscopically visible, w...
Pulmonary intravascular macrophages in horses and ponies. Seven horses (4 anesthetized and 3 awake) and 2 ponies (anesthetized) were studied to evaluate the high sensitivity of the pulmonary circulation of the horse to various blood-borne particles, and to establish the presence of intravascular macrophages in the lung. Pulmonary and systemic pressures and cardiac output before and during particle injection were measured in some animals. An anesthetized foal had a large increase in pulmonary arterial pressure (32 and 34 mm of Hg) within 1 minute of IV administration of small test doses of radioactively labeled liposomes (2.5 mumol/kg of body weight) ...
[The oxygen pathway: how well-built is the respiratory system?]. The question is explored of how the structural systems that constitute the pathway for oxygen from the air through the lung and the circulation of blood to the mitochondria in muscle cells affect the O2 flow rate, and whether their quantitative structural characteristics conform to the hypothesis of symmorphosis which postulates a match of structural design to overall functional demand. By combining physiological and morphometric studies, it is first demonstrated that the diffusing capacity of the human lung is slightly larger than that needed for maximal O2 uptake. Comparative studies of smal...
The effects of furosemide and pentoxifylline on the flow properties of equine erythrocytes: in vitro studies. The effects of various concentrations of furosemide and pentoxifylline on equine RBC in vitro were evaluated to facilitate better understanding of the potential effects of these drugs on blood flow properties. Furosemide induced increased mean cell volume (MCV), increased RBC potassium concentration, increased whole blood viscosity, and decreased the RBC filtrability. These data indicate that furosemide may block the RBC membrane transport pathways resulting in potassium and water retention. The increase in size and the resultant decrease in the surface-area-to-volume ratio may have caused the...
Muscular changes in Venezuelan wild horses naturally infected with Trypanosoma evansi. Skeletal muscle biopsy specimens were taken from 10 male horses naturally infected with Trypanosoma evansi and from 10 uninfected males. An indirect fluorescent antibody test was used to provide a rapid and reliable indication of infection. Histological, histochemical and transmission electron microscopical techniques were used to examine skeletal muscle. The ultrastructural features in muscle fibres were those usually seen in autoimmune disease, namely fibre and capillary necrosis and mononuclear cell infiltration, consisting of macrophages. Changes in fibre-type percentages did not occur in ...
Vasomotor effects of histamine on bovine and equine basilar arteries in vitro. The vasomotor effects of histamine on isolated bovine and equine basilar arteries were examined. Histamine induced contractions in both these preparations. The maximal response to and pEC50 value for histamine of the equine artery were larger than those of bovine tissue. Similar results were obtained with endothelium-denuded basilar arteries. Diphenhydramine (H1-receptor antagonist) inhibited histamine-induced contractions of the basilar arteries from both species in a concentration-dependent manner and its pA2 values (with 95% confidence limits) were 7.61 (7.39-7.83) and 8.15 (8.01-8.29) for ...
Substance P immunohistochemical study of the sensory innervation of normal subchondral bone in the equine metacarpophalangeal joint. Serial sections of bone and soft tissue from the metacarpophalangeal joints of 2 mature and 2 immature horses were evaluated for substance P immunoreactive sensory nerve fibers. Formalin-fixed specimens were sectioned, either nondemineralized or demineralized with formic acid or EDTA. Rabbit antiserum to substance P (SP) was used in the streptavidin-biotin-peroxidase complex method for immunolocalization of SP antigen, and staining with 3,3'-diaminobenzidine was used for permanent identification of SP fibers. Abundant sensory nerve fibers were identified in the joint capsule, synovial membrane...
Substance P innervation of equine synovial membranes: joint differences and neural and nonneural receptor localizations. Substance P (SP) immunocytochemistry and receptor autoradiography were used to define the innervation of the equine synovial membrane of joints equivalent to the wrist and knuckle of man. SP-immunoreactive fibers were mainly concentrated around blood vessels in the subsynovial layer, although not exclusively, while in the more distal joint, SP fibers were more frequently seen in the synovial surface layer. Iodinated SP receptor autoradiography studies revealed silver grain concentrations in the advential layer of blood vessels associated with the vasa vasorum, on the vascular endothelium and i...
Ischemia/reperfusion injury of the ascending colon in ponies: a correlative study utilizing microvascular histopathology and corrosion casting. Volvulus of the ascending colon (ACV) in the horse results in microvascular injury and necrosis of the intestinal mucosa. This study investigated the site and type of microvascular injury which occurs within the mucosa and submucosa following ACV. Histopathology of volvulus treated ponies demonstrated mucosal necrosis with microvascular hemorrhage and thrombosis. Thrombi occurred within the subepithelial capillaries and edema and hemorrhage developed throughout the mucosa and submucosa. Vascular casts allowed 3-D viewing of samples obtained from the entire pelvic flexure and demonstrated two d...
