Topic:Adenine Nucleotides
Adenine nucleotides, including ATP, ADP, and AMP, are pivotal molecules that drive cellular energy metabolism and regulate a myriad of biochemical processes in horses and other organisms. They facilitate energy transfer, signal transduction, and metabolic control, underpinning essential physiological functions such as muscle contraction, nerve transmission, and overall cellular homeostasis. This page compiles peer-reviewed research studies and scholarly articles that explore the roles, regulation, and clinical significance of adenine nucleotides in equine physiology and metabolic health.
Substitutions of isoleucine residues at the adenine binding site activate horse liver alcohol dehydrogenase. The contributions of isoleucine residues 224 and 269 of horse liver alcohol dehydrogenase to binding of the adenine moiety of NAD and to catalysis were studied by replacing Ile-224 with glycine (I224G) and Ile-269 with serine (I269S). The kinetic mechanisms of wild-type and both mutated liver enzymes were ordered. Affinities for several adenosine derivatives were decreased 5-50-fold by both substitutions. The I269S mutation differentially destabilized binding of the complete coenzyme, as affinities for NAD+ and NADH were decreased about 60-fold with the I224G enzyme and 350-fold for the I269S ...
Endotoxin-induced platelet aggregation in heparinised equine whole blood in vitro. Endotoxaemia is a leading cause of death among horses. Thrombocytopenia is a common finding in clinical and experimentally-induced cases of endotoxaemia and can lead to coagulopathies, including disseminated intravascular coagulopathy which is usually fatal. In this study it was shown that endotoxin (3 ng ml-1 to 25 micrograms ml-1) can aggregate equine platelets in heparinised whole blood in vitro. The endotoxin-induced aggregation (EIA) was shown to be dependent on the presence of leucocytes in the blood and did not occur when detoxified endotoxin was used, suggesting that lipid A was necess...
Extracellular ATP can activate autonomic signal transduction pathways in cultured equine sweat gland epithelial cells. Changes in intracellular free calcium concentration ([Ca2+]i) were monitored in a cell line that was derived from the equine sweat gland epithelium. ATP and closely related compounds could increase [Ca2+]i with a rank order of potency of UTP > or = ATP > ADP >> AMP = adenosine = alpha,beta-methylene-ATP. The responses to ATP and to UTP were initiated by the release of calcium from an internal store and subsequently sustained by calcium influx. The rise in [Ca2+]i thus seems to be mediated by P2U receptors that are coupled to phosphoinositidase C. Some desensitisation of this respon...
Accumulation of allantoin and uric acid in plasma of exercising trotters. Plasma concentrations of hypoxanthine, uric acid, and allantoin, which are breakdown products of adenine nucleotides, were measured in Standardbred and Finnhorse trotters during and after an exercise test on a high-speed treadmill, after an incremental exercise test performed on a racetrack, and after a racing competition. Fiber-type composition of the middle gluteal muscle and the muscle concentrations of adenine nucleotides and inosine monophosphate were measured after the racetrack test. Changes in the concentration of hypoxanthine were not observed in any of the tests. Peak concentration o...
Adenine nucleotide degradation in the thoroughbred horse with increasing exercise duration. Adenine nucleotide (AN) degradation has been shown to occur during intense exercise in the horse and in man, at or close to the point of fatigue. The aim of the study was to compare the concentrations of muscle inosine 5'-monophosphate (IMP) and plasma ammonia (NH3) during intense exercise with the concentrations of muscle and blood lactate. Seven trained thoroughbred horses were used in the study. Each exercised on a treadmill for periods of between 30 s and 150 s, at 11 and/or 12 m.s-1. Blood and muscle samples were taken and analysed for lactate and NH3 and adenosine 5'-triphosphate (ATP), ...
Titrimetric determination of muscle buffering capacity (beta mtitr) in biopsy samples. In vitro titration of muscle homogenates has been used to assess muscle buffering capacity (beta mtitr) in a variety of species. In the present study, factors likely to affect the estimation of beta mtitr were investigated. Also, values of beta mtitr from normal Thoroughbred horses are presented. A non-linear titration curve was obtained with addition of HCl to muscle homogenates. As a result, beta mtitr is expressed as the mumol H+ required to change the pH of 1g of dry muscle or wet muscle from 7.1 to 6.5. An effect of dilution on the initial pH was found below 40 mg wet muscle per ml homoge...
Muscle ATP loss and lactate accumulation at different work intensities in the exercising Thoroughbred horse. The effect of 2 min treadmill exercise, at speeds of 6-12 m.s-1 on an incline of 5 degrees, upon muscle adenine nucleotide loss and lactate accumulation was studied in six Thoroughbred horses. Minimal change occurred in the adenosine triphosphate (ATP) content of the middle gluteal muscle at speeds of 10 m.s-1 or less, but significant loss (up to 47%) had occurred in all horses by 12 m.s-1. The decline in ATP significantly correlated with the accumulation of muscle lactate, beginning shortly after the accumulation of 40 mmol.kg-1 dry muscle lactate. Decline in muscle ATP was mirrored closely b...
The influence of metabolic alkalosis upon exercise metabolism in the thoroughbred horse. Six thoroughbred horses exercised on a motorised treadmill on two separate occasions at a speed of 11 or 12 m.s-1 for up to 2 min. 4 h prior to exercise each horse was given a 21 test solution of sodium bicarbonate (NaHCO3; 0.6 g.kg-1 body mass) or a control solution of water by nasogastric intubation, the order of administration of the two solutions was randomised. Blood samples (n = 15) were obtained before and during the 4 h after intubation, during exercise and for 30 min after exercise. NaHCO3 ingestion resulted in changes in pre-exercise acid-base status. The changes in blood lactate and...
Iodide-induced inhibition of adenylate cyclase activity in horse and dog thyroid. The characteristics of the iodide-induced inhibition of cyclic AMP accumulation in dog thyroid slices have been previously described [Van Sande, J., Cochaux, P. and Dumont, J. E. (1985) Mol. Cell. Endocrinol. 40, 181-192]. In the present study we investigated the characteristics of the iodide-induced inhibition of adenylate cyclase activity in dog and horse thyroid. The inhibition of cyclic AMP accumulation by iodide in stimulated horse thyroid slices was similar to that observed in dog thyroid slices. The inhibition was observed in slices stimulated by thyroid-stimulating hormone, cholera tox...
Furosemide: effects on the hemostatic mechanism of resting and exercised standardbred horses. Two groups of 6 Standardbred horses each were used to study hemostatic functions at rest and after exercise with furosemide or a placebo. One group which was trained was given maximum exercise on the racetrack, and the other, a less-fit group, was given submaximum exercise on the treadmill. There was no difference in furosemide compared to placebo trial results in either group in coagulation screening tests, platelet concentration, or retention of platelets in a glass bead column. Increased fibrinogen concentration and enhanced platelet retention were associated with maximum exercise. Aggregat...
Increased susceptibility of fibroblasts from horses with severe combined immunodeficiency to growth inhibition by 2′-deoxyadenosine. The effect of adenosine, deoxyadenosine, guanosine, and deoxyguanosine on the growth rate of fibroblasts derived from normal horses, horses heterozygous for the severe combined immunodeficiency (SCID) trait (heterozygotes), and horses with SCID was studied. All four purines were found to inhibit growth in a dose-dependent manner, but only adenosine and deoxyadenosine were inhibitory at concentrations of less than 100 microM. No statistical difference in sensitivity to adenosine was detected between normal and SCID fibroblasts. Fibroblasts from SCID horses were, however, more sensitive to the g...
High-performance liquid affinity chromatography on silica-bound alcohol dehydrogenase. Horse liver alcohol dehydrogenase was immobilized on glycerylpropyl-silica (10 micron, 1000-A pores) activated with 2,2,2-trifluoroethanesulfonyl chloride (tresyl chloride). The coupling and activity yield was almost 100%. The coenzyme-binding sites were equivalent and virtually unaffected by the immobilization process, as judged from Scatchard plots and active-site titrations. The silica-bound enzyme, packed in steel columns, was integrated with HPLC equipment and then successfully used for chromatography of adenine nucleosides, adenine nucleotides, and triazine dyes. Dissociation constants w...
Concentration of nucleotides and deoxynucleotides in peripheral and phytohemagglutinin-stimulated mammalian lymphocytes. Effects of adenosine and deoxyadenosine. Concentrations of purine and pyrimidine ribonucleotides were measured with HPLC in lymphocytes of man, horse, pig and sheep and in rat thymocytes. The ATP concentration was highest in lymphocytes of all species and about 850 pmol/10(6) cells in human and equine lymphocytes, higher in porcine and lower in ovine lymphocytes and rat thymocytes. The GTP concentration was comparable in human, equine and porcine lymphocytes, but lower in ovine lymphocytes. ATP concentration was also measured in lymphocytes of man, horse and pig with a luciferin-luciferase assay. During culturing with or without phyt...
Effects of adenosine and deoxyadenosine on PHA-stimulation of lymphocytes of man, horse and pig. 1. Adenosine inhibits thymidine and uridine incorporation of PHA-stimulated lymphocytes of man and horse at concentrations higher than 50 and 10 microM, respectively. Deoxyadenosine is inhibitory at concentrations higher than 100 microM. Thymidine and uridine incorporation of porcine lymphocytes are elevated 5-7-fold by 25-100 microM adenosine, deoxyadenosine, inosine and hypoxanthine. Leucine incorporation of PHA-stimulated lymphocytes was affected by adenosine and deoxyadenosine in the same way, but to a lower extent. 2. Effects of adenosine and deoxyadenosine were more pronounced at shorter...
Metabolism of purine nucleosides and phosphoribosylpyrophosphate in thymocytes and splenocytes of various mammalian species. 1. Activities of ADA, PNP and AK were measured in splenocytes and thymocytes of newborn children, young horses, pigs, sheep, rats and mice and compared with the activities previously found in peripheral lymphocytes. 2. With all species, except horse, the activity of ADA (per 10(6) cells) was higher in thymocytes than in lymphocytes. Activity of ADA was highest in splenocytes of pig and sheep. Activity of ADA was lowest in all lymphoid cells of the horse and only about 10% of the activity in human splenocytes and lymphocytes. 3. With all species, except horse, the activity of PNP was lower in t...
In vitro of adenosine on lymphocytes and erythrocytes from horses with combined immunodeficiency. The effect of adenosine on the mitogenic response of peripheral blood lymphocytes (PBL) and on the nucleotide pools of erythrocytes from normal horses, horses heterozygous for the combined immunodeficiency (CID) trait (carriers), and foals with CID was studied. When PBL from normal, carrier, and CID horses were stimulated by phytohemagglutinin (PHA), concanavalin A, or pokeweed mitogen, [3H]thymidine uptake was inhibited by adenosine (0.1 microM) to 1.0 mM) in a dose-dependent manner. Adenosine (100 microM) mediated inhibition of [3H]thymidine uptake was prevented in both normal and carrier ho...
Circular dichroic properties and conformation of thionicotinamide dinucleotides bound to horse-liver alcohol dehydrogenase. The interaction between horse liver alcohol dehydrogenase and the oxidized and reduced forms of the 3-thionicotinamide--adenine dinucleotide coenzyme analogues (sNAD and sNADH) has been investigated by ultraviolet absorption, fluorescence and circular dichroism. The fluorescence of sNADH is enhanced when bound to the enzyme, and the protein fluorescence is quenched by both sNADH (60--65%) and sNAD (65%). The possible origin of the larger quenching produced by sNAD with respect to that of NAD is discussed. Coenzyme dissociation constants have been determined by monitoring the quenching of the p...
Fiber types and size in equine skeletal muscle. Frozen sections of equine musculus semitendinosus were examined for myosin adenosine triphosphatase (ATPase) and reduced nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), using standard histochemical procedures, and the proportions of the various fiber types and average fiber sectional size were determined. With ATPase staining, approximately 70% of the fibers were classified as alpha fibers (ATPase positive), and 30%, as beta fibers (ATPase negative). In addition, 2 populations of alpha fibers could be readily distinguished on the basis of the intensity of the ATPase reaction...
[Histochemical and ultrastructural study of the acid phosphatase, alkaline phosphatase, and adenosine triphosphatase contents in the pars proventricularis epitheiium of the horse stomach]. Summary. The activities and localization of a lysosomal acid phosphatase and of a Mg++- and Ca++-activated ATPase were shown in the pars proventricularis epithelium of the horse stomach using cytochemical methods and the light and electron microscopes. Activity of the non-specific alkaline phosphatase was exclusively demonstrated on the subepithelial vessel loops of the papillae occultae.
The activityof ATPases gradually decreased from the stratum basale to the stratum super- ficiale. Reaction intensity was optimal after 45 rain and did not increase further. An increase of the Mg++-activated ...