Topic:Arginine
Arginine is an amino acid that is involved in various physiological processes in horses. It is a precursor for the synthesis of nitric oxide, a molecule that plays a role in vasodilation and blood flow regulation. Arginine is also involved in protein synthesis, immune function, and the urea cycle, which is essential for removing ammonia from the body. In equine nutrition, arginine is considered a conditionally essential amino acid, particularly during periods of growth, stress, or illness when the body's demand may exceed its ability to produce it. This page compiles peer-reviewed research studies and scholarly articles that explore the metabolism, dietary requirements, and potential health implications of arginine in horses.
Effect of insulin-induced hypoglycaemia on secretion patterns and rates of corticotrophin-releasing hormone, arginine vasopressin and adrenocorticotrophin in horses. To study the effect of hypoglycaemia on secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH in a non-ruminant species, a non-surgical method was used to collect pituitary venous (PitVen) blood every 0.5 or 1 min from seven horses before and after insulin administration (0.4 U/kg i.v.). To assess the effect of PitVen cannulation on results, peripheral hormones were also measured before and after insulin in five horses without PitVen cannulae. Insulin administration lowered plasma glucose in all horses (P < 0.0001; paired t-test). Cortisol concentrat...
Evaluation of arginine-glycine-aspartate-containing peptides as inhibitors of equine platelet function. To determine whether synthetic peptides containing the arginine-glycine-aspartate (RGD) sequence inhibit equine platelet function. Methods: For in vitro studies of blood, 3 healthy Thoroughbreds; for in vivo and ex vivo studies of administration of RGD-containing peptides, 4 young adult pony mares. Methods: Blood was incubated with and without addition of aspirin or RGD-containing peptides (RGDS, RPR 110885) and platelet aggregation responses and platelet adhesion to subendothelial collagen were determined. RPR 110885 was administered IV, and platelet function was evaluated. Platelet aggregati...
Nitric oxide and thermoregulation during exercise in the horse. The effect of inhibition of nitric oxide production on sweating rate (SR) and on core, rectal, and tail skin temperatures was measured in five Thoroughbred horses during exercise of variable intensity on a high-speed treadmill. A standard exercise test consisting of three canters [approximately 55% maximum O2 uptake (VO2max)], with walking (approximately 9% VO2max) and trotting (approximately 22% VO2max) between each canter, was performed twice (control or test), in random order, by each horse. N(G)-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg), a competitive inhibitor of nitric oxide synth...
Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes. Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2% halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, beta-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after ...
Effects of nitric oxide inhibition on thermoregulation during exercise in the horse. We investigated the role of NO in the control of thermoregulation. We measured sweating rate and body temperatures (core, rectal and skin) in five thoroughbred horses during exercise of variable intensity on a high-speed treadmill. A standard exercise test (SET) consisting of three canters (8 m s-1), with walking and trotting between each canter, was performed twice, in random order, by each horse and N omega-nitro-L-arginine methyl ester (L-NAME; 20 mg ml-1), a competitive inhibitor of nitric oxide synthase (NOS), was infused into the central circulation after the first canter in the test SET...
Atrial natriuretic peptide and C-type natriuretic peptide do not acutely inhibit the release of adrenocorticotropin from equine pituitary cells in vitro. It has been suggested that atrial natriuretic peptide (ANP) is the long-sought inhibitor of corticotropin (ACTH) secretion, but the evidence is conflicting. We have examined the effect of ANP and C-type natriuretic peptide (CNP) on the secretion of ACTH by perifused equine pituitary cells in an in vitro milieu intended to mimic the in vivo milieu in the horse. Corticotropin-releasing hormone (20 pM) and cortisol (0 or 100 nM) were perifused continuously and 7 pulses of arginine vasopressin (AVP; 10 nM) applied for 5 min at 30-min intervals. ANP (1 nM) or CNP (1 nM) were perifused continuously ...
Glyceryl trinitrate enhances nitric oxide mediated perfusion within the equine hoof. Laminitis, a microvascular disease of the equine hoof leads to severe lameness. Exogenous iv 1-arginine and transdermal nitric oxide donors, such as GTN, applied to the pasterns improve lameness during acute laminitis. Near Infrared spectroscopy in an earlier study showed haemostasis and ischaemia in the hoof during acute laminitis, both were alleviated by 1-arginine. Quantitative NIRS in the present study shows that transdermal GTN increases blood flow in the equine hoof. It is concluded that glyceryl trinitrate enhances nitric oxide mediated perfusion within the equine hoof in normal and chr...
Cardiorespiratory, endocrine and metabolic changes in ponies undergoing intravenous or inhalation anaesthesia. Six Welsh gelding ponies (weight 246 +/- 6 kg) were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) followed by 0.02 mg/kg of detomidine i.v. Anaesthesia was induced with 2 mg/kg of ketamine i.v. Ponies were intubated and lay in left lateral recumbency. On one occasion anaesthesia was maintained for 2 h using 1.2% halothane in oxygen. The same group of ponies were anaesthetized 1 month later using the same induction regime and anaesthesia was maintained with a combination of detomidine, ketamine and guaiphenesin, while the ponies breathed oxygen-enriched air. Electrocardiogra...
Nitric oxide donors as treatment for grass induced acute laminitis in ponies. The potential for participation of the arginine-nitric oxide system in the aetiology of acute equine laminitis has been assessed. Nitric oxide (NO), produced by the action of NO synthase (NOS) on its substrate l-arginine, relaxes vascular smooth muscle to cause vasodilation. An attenuated normal vasodilatory tone may characterise the pathogenesis of acute equine laminitis. An intravenous infusion of 10% l-arginine in 0.9% saline caused vasodilatation in the hoof of a normal pony and immediate reperfusion of laminal tissues in an acutely laminitic pony, detected noninvasively by near infrared s...
Dynamics of the regulation of the hypothalamo-pituitary-adrenal (HPA) axis determined using a nonsurgical method for collecting pituitary venous blood from horses. Since 1985, we have applied our nonsurgical technique for collecting pituitary venous (PitVen) blood from ambulatory horses to investigate the regulation of adrenocorticotropic hormone (ACTH) secretion. This method offers particular advantages for studying the hypothalamo-pituitary-adrenal axis since its benign nature enables hypothalamic and pituitary interactions to be monitored without disturbing the animal, and the horse's large blood volume allows 3- to 4-ml samples to be collected as frequently as every 20s for prolonged periods so that the secretion patterns of ACTH and its secretagogue...
Involvement of nitric oxide in the non-adrenergic non-cholinergic neurotransmission of horse deep penile arteries: role of charybdotoxin-sensitive K(+)-channels. 1. The involvement of nitric oxide (NO) and the signal transduction mechanisms mediating neurogenic relaxations were investigated in deep intracavernous penile arteries with an internal lumen diameter of 600-900 microns, isolated from the corpus cavernosum of young horses. 2. The presence of nitric oxide synthase (NOS)-positive nerves was examined in cross and longitudinal sections of isolated penile arteries processed for NADPH-diaphorase (NADPH-d) histochemistry. NADPH-d-positive nerve fibres were observed in the adventitia-media junction of deep penile arteries and in relation to the trabec...
The effect of naloxone administration on the secretion of corticotropin-releasing hormone, arginine vasopressin, and adrenocorticotropin in unperturbed horses. We used our nonsurgical method for collecting equine pituitary venous blood to study the role of endogenous opioids in the basal regulation of the hypothalamo-pituitary-adrenal axis. We gave mares the opioid antagonist, naloxone (NAL), at either a high (0.5 mg/kg i.v. bolus, followed by infusion of 0.25 mg/kg.h; n = 4) or low (0.2 mg/kg i.v. bolus; n = 6) dose rate. Pituitary venous blood was collected continuously, divided into 0.5- or 1-min segments for 15-30 min before and 1 h after the NAL bolus, and assayed for CRH, arginine vasopressin (AVP), and ACTH. The mares tolerated NAL administrat...
Pituitary-adrenal activity and opioid release in ponies during thiopentone/halothane anaesthesia. The effect of thiopentone/halothane anaesthesia on the release of endogenous opioid, adrenocorticotrophin, arginine vasopressin, cortisol and catecholamine was investigated in ponies. The contribution made by halothane itself was studied by maintaining six ponies with a constant 1.2 per cent end tidal halothane concentration and five with a concentration ranging between 0.8 and 1.2 per cent. Cardiorespiratory depression was more prolonged in the ponies receiving a constant 1.2 per cent end tidal halothane concentration than in those which received less halothane. Plasma lactate concentration i...
The effects of corticotrophin-releasing hormone, arginine vasopressin and their antagonists on ACTH release from perifused horse anterior pituitary cells. Antagonists are useful for probing hormone action and receptor characteristics. In this study we have investigated the inhibitory effects of analogues of arginine vasopressin (AVP) and corticotrophin-releasing hormone (CRH) on stimulated release of immunoreactive ACTH from perifused equine anterior pituitary cells in vitro. Our aims were to gain some insight into the characteristics of the CRH and AVP receptors of the horse pituitary and to establish whether the response induced by AVP and CRH together could be blocked by combining antagonists. Experimental design included 5-min pulses of AVP ...
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...
Short-term secretion patterns of corticotropin-releasing hormone, arginine vasopressin and ACTH as shown by intensive sampling of pituitary venous blood from horses. To characterize the short-term ACTH secretion pattern and to investigate factors regulating it, pituitary venous (PV) blood was collected using our nonsurgical method from 8 unperturbed horses every 20 or 30 s for approximately 1 h. In all but 1 horse, sampling occurred during the broad circadian maximum in plasma cortisol concentrations. Concentrations of corticotropin-releasing hormone (CRH; n = 7 horses), arginine vasopressin (AVP), ACTH and cortisol were measured by radioimmunoassay. In all horses, CRH, AVP and ACTH secretion patterns appeared irregular in time and amplitude. The mean (+/-...
Histochemical and functional evidence for a cholinergic innervation of the equine ureter. The distribution of acetylcholinesterase (AChE)-positive nerve fibers and cells, as well as the effects of acetylcholine (ACh) on ureteral smooth muscle and small resistance arteries were investigated in the equine ureter by means of histochemical, classic organ baths and myograph techniques. AChE-positive nerve fibers were widely distributed throughout the ureteral wall forming muscular, subepithelial and perivascular nerve plexuses, whose density was highest at the intravesical ureter. AChE-positive nerve cells were also identified grouped as adventitial or intramural ganglia. ACh increased ...
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...
Studies on the transport in vitro of lysine, histidine, arginine and ammonia across the mucosa of the equine colon. Discs of stripped mucosa from the proximal ventral colon were prepared immediately after slaughter of 8 Shetland cross-breed ponies. The mucosae were fixed in incubation chambers and used in incubation experiments to study the transmucosal fluxes of the amino acids lysine, histidine and arginine (150 min) and of ammonia (90 min). When the amino acid concentrations in the mucosal solution were in the physiological range (2.8-3.0 mmol/l) no transport to the serosal side of the tissue was found. When the concentrations were raised 10-fold, less than 2% of the mucosal amino acid pool was recovered...
Inhibitory nerve distribution and mediation of NANC relaxation by nitric oxide in horse airways. The distribution of inhibitory nerves and the mediator of the inhibitory nonadrenergic noncholinergic (iN-ANC) nervous system were investigated in smooth muscle preparations from seven regions of equine airways. In tissues incubated with atropine and precontracted with histamine, electrical field stimulation produced frequency-dependent relaxation, and the magnitude of the relaxation decreased from trachea to central bronchi and was absent in peripheral airways. The degree of relaxation in bronchi was not simply a function of bronchial size or generation. Propranolol inhibited part of the rela...
Furosemide magnifies the exercise-induced elevation of plasma vasopressin concentration in horses. The purpose of this study was to test the hypothesis that furosemide administration before exercise would cause greater increases in plasma arginine vasopressin (AVP) concentration in exercising horses than exercise alone. Six adult, clinically normal, unfit mares underwent three randomly ordered 60 minute standard exercise tests on an equine treadmill to examine the effect of furosemide administration on plasma AVP concentration. In one trial, furosemide (1 mg kg-1) was infused four hours before exercise (FUR-4) and a placebo (10 ml saline) was infused two minutes before exercise; in another ...
The acute effect of lowering plasma cortisol on the secretion of corticotropin-releasing hormone, arginine vasopressin, and adrenocorticotropin as revealed by intensive sampling of pituitary venous blood in the normal horse. The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P < 0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P < 0.02). Three mares became mildly agitated during treatment. Mean PV concentratio...
The effect of cortisol on the secretion of ACTH by anterior pituitary cells of the horse in culture. Perifused equine anterior pituitary cells were used to investigate the effect of cortisol on the ACTH response to pulses of corticotrophin-releasing hormone (CRH; 0.01 nmol/l) and arginine vasopressin (AVP; 100 nmol/l), given for 5 min every 30 min for 690 min and ACTH measured in 5-min fractions. At the fourth pulse of secretagogue (0 min), a constant perifusion with cortisol began (0 nmol/l (control), 100, 200, 500, 5000 and 50,000 nmol/l) and continued until the ninth pulse (150 min). For each pulse of secretagogue, the amount of ACTH (pmol) secreted in response to each pulse (ACTH response...
Factors affecting ACTH release from perifused equine anterior pituitary cells. The multifactorial control of ACTH is well established. We wished to establish and characterize an in-vitro perifusion system, using equine anterior pituitary cells and physiological concentrations of secretagogues, to investigate factors which affect the dynamics of ACTH secretion. Anterior pituitary tissue was divided for dispersion into cells with collagenase, trypsin or dispase, or by mechanical dispersion. After dispersal followed by 18-h incubation, cells were perifused and the ACTH response to 10-min pulses of arginine vasopressin (AVP; 100 nmol/l), corticotrophin-releasing hormone (CRH...
Effect of protein source in liquid formula diets on food intake, physiologic values, and growth of equine neonates. The effects of 2 liquid formula diets differing in protein source were evaluated in orphan foals. The response of 7 foals fed a diet containing casein as the protein source, and 6 foals fed a diet containing a combination of whey and casein, was compared with the response in a reference group of 8 mare-raised foals. Orphaned foals were fed 150 kcal/kg of body weight/d, divided into 6 equal feedings of 25 kcal/kg. Formula intake was comparable among the experimental groups, and foals fed the liquid formula diet grew as well as mare-raised foals. There was no difference among groups in mean dail...
Acholeplasma multilocale sp. nov., isolated from a horse and a rabbit. Acholeplasma strains were isolated from the nasopharynx of a horse (strain PN525T [T = type strain]) and the feces of a rabbit (strain B1). One clone of strain PN525T and one clone of strain B1 were examined in detail. These clones were indistinguishable from each other and were serologically distinct from the previously described Acholeplasma and Mycoplasma spp. The strains had the following properties: guanine-plus-cytosine content of 31 mol%; sterol was not required for growth, which occurred under both aerobic and anaerobic conditions; glucose was metabolized; and arginine was hydrolyzed. ...
Concentrations of amino acids in the plasma of neonatal foals with septicemia. Concentrations of amino acids in the plasma of 13 neonatal foals with septicemia were compared with the concentrations of amino acids in the plasma of 13 age-matched neonatal foals without septicemia. Analysis of the results revealed significantly lower concentrations of arginine, citrulline, isoleucine, proline, threonine, and valine in the plasma of foals with septicemia. The ratio of the plasma concentrations of the branched chain amino acids (isoleucine, leucine, and valine) to the aromatic amino acids (phenylalanine and tyrosine), was also significantly lower in the foals with septicemia....
The effect of acute exercise on the secretion of corticotropin-releasing factor, arginine vasopressin, and adrenocorticotropin as measured in pituitary venous blood from the horse. We have used the technique which we have developed for collecting pituitary venous blood from conscious, undisturbed horses to study the effect of acute vigorous exercise on the secretion of CRF, arginine vasopressin (AVP) and ACTH. Pituitary venous (pit) blood was collected every 1-5 min from nine trained racehorses at rest in the stable. The horses then trotted quietly for 10 min, after which they galloped as fast as possible for 4-6 min, before returning to the stable where sampling continued. In Exp 1 (n = 5) no blood samples were taken during exercise, whereas in Exp 2 (n = 4), pit blood ...
Clinical nutrition of adult horses. Horses suffering from trauma, sepsis, and severe burns need 12% to 16% of protein (dry matter basis) in their diet. Since reduced appetite may be a problem, relatively energy dense (greater than 2 Mcal DE/kg) feeds should be offered. In hepatic failure, maintenance protein requirements (8% on a dry matter basis for adult horses) should be met with feeds that are high in short branched-chain amino acids and arginine but low in aromatic amino acids and tryptophan (for example, milo, corn, soybean, or linseed meal) in addition to grass hay. Vitamins A, C, and E should also be supplemented. In cas...
Mycoplasmas from donkeys and horses in the Sudan. Seventeen isolates (4.27%) were recovered from 398 samples. Twelve isolates (4%) were obtained from 300 donkey nasal swabs, three (4.3%) and two (6.89%) isolates were recovered from 69 horse nasal swabs and 29 mare uterine washings, respectively. Nine isolates were lost during storage at -20 degrees C and the remaining eight were identified as mycoplasmas and their biological, biochemical and serological reactions were investigated. The isolates could be divided into two groups on the basis of glucose fermentation and arginine hydrolysis. The first group neither fermented glucose nor hydrolyse...