A. Reeta Pösö

Accumulation of uric acid in plasma after repeated bouts of exercise in the horse.

Plasma concentration of uric acid, total peroxyl radical-trapping antioxidative parameter (TRAP), blood lactate concentration and plasma activity of xanthine oxidase (XO) were measured in six Standardbreed trotters after six bouts of exercise with increasing intensity on two separate days three days apart. Blood samples were taken immediately, 5, 10, 15, 30 and 60 min after each heat and 2, 4, and 6 hr after the last heat. Exercise caused an increase in TRAP and in the concentrations of lactate and uric acid. Plasma uric acid concentration increased exponentially with respect to time after the last heat performed maximal speed, indicating a rapid increase in the rate of purine degradation. Plasma XO activity increased during exercise, but the intensity of exercise had only a minor effect on the level of XO activity. In conclusion, these data suggest that a threshold for the plasma accumulation of uric acid in terms of the intensity of exercise may exist and that XO may play a role in the formation of uric acid in horse plasma. Intense exercise causes an increase in the plasma antioxidant capacity that in the horse is mainly caused by the increase in the plasma uric acid concentration.

Fluid, Electrolyte, and Acid-Base Responses to Exercise in Racehorses

During both high-intensity and short-distance exercise, the high rate of expended energy is met by anaerobic oxidation of glucose to lactic acid; this is the main cause of metabolic acidosis observed during racing. In addition, plasma volume decreases because water moves from the vasculature to the intracellular and interstitial spaces at the onset of intense exercise. These fluid shifts, together with active ion-exchange between blood and tissue, cause marked changes in electrolyte concentrations. This article reviews the mechanisms of acid-base disturbances, fluid shifts, and electrolyte changes, and discusses related areas such as buffer capacity, lactic acid distribution, and the effects of training. The influences of health, dietary cation-anion balance, supplements, and medication such as creatine, sodium bicarbonate, and furosemide are emphasized.

Alcohol Intoxication and Hangover: Effects on Plasma Electrolyte Concentrations and Acid-Base Balance

The relationships between the symptoms of hangover and the concentrations of Na+, K+, Cl−, Ca++, and Mg++ ions in plasma and the acid-base balance in capillary blood were studied in 19 healthy volunteers, who, after fasting 10 hours, consumed 1.5 g/kg body wt of ethanol. The intensity of alcohol intoxication and hangover were estimated by using simple rating scales. No significant changes were found in electrolyte concentrations during the observation period of 20 hours. A significant metabolic acidosis, however, was found to occur simultaneously with the most severe hangover. The correlation between the degree of acidosis and the intensity of hangover was statistically significant. It is concluded that hangover is not caused by alterations in plasma electrolyte concentrations but that acidosis, although not being the primary cause of hangover, may contribute to the symptoms. In addition, the results suggest that acid-base analysis might be used as an objective measure of hangover intensity.

Interindividual variation in total and carrier-mediated lactate influx into red blood cells

To study in standardbred horses interindividual variation in the influx of lactate into red blood cells, venous blood samples were collected from 89 horses from 2 wk to 9 yr of age. For 62 horses, the rate of influx was normally distributed with a mean rate of 4.09 nmol.mg protein-1.min-1 at a lactate concentration of 10 mM, and the respective value for the other 27 horses was 0.58 nmol.mg protein-1.min-1. At 30 mM of lactate, the rates were 8.71 and 1.97 nmol.mg protein-1.min-1, respectively. This bimodal distribution was independent of age. In horses with high transport activity, the monocarboxylate transporter (MCT) appears to be the major carrier, whereas, in those with low transport activity, no activity of the MCT could be detected. The band 3 protein may account for 18-39% of transport activity. With all age groups combined, the transport activity tended to be higher in mares than in stallions. Lactate transport into red blood cells seems thus to be an inherent property in which participation of various transporters varies interindividually.

Plasma levels of heat shock protein 72 (HSP72) and β-endorphin as indicators of stress, pain and prognosis in horses with colic.

A prospective observational study was performed to evaluate whether the plasma concentration of heat shock protein 72 (HSP72) or beta-endorphin is related to clinical signs, blood chemistry, or severity of pain of colic. Seventy-seven horses with colic and 15 clinically healthy controls were studied. The horses were divided into four groups which reflected increasing severity of colic, from normal control horses to horses with mild, moderate and severe colic. Blood samples were collected before any treatment. Packed cell volume (PCV) and plasma HSP72, beta-endorphin, cortisol, adrenocorticotropic hormone (ACTH) and lactate concentrations were measured. Plasma beta-endorphin was related with severity of colic and survival, as well as with plasma cortisol, ACTH and lactate concentrations, heart rate, PCV and pain score. High plasma HSP72 concentration may indicate circulatory deficits, but was not associated with clinical signs of colic. Plasma lactate still seemed to be the most useful single prognostic parameter in horses with colic.

Lactate transport in canine red blood cells.

OBJECTIVE To detect monocarboxylate transporters (MCTs) in canine RBC membranes and to determine the distribution of lactate between plasma and RBCs. SAMPLE POPULATION Blood samples obtained from 6 purpose-bred Beagles. PROCEDURES Monocarboxylate transporter isoforms 1, 2, 4, 6, 7, and 8 and CD147 were evaluated in canine RBCs by use of western blot analysis. Lactate influx into RBCs was measured as incorporation of radioactive lactate. RESULTS 2 MCT isoforms, MCT1 and MCT7, were detected in canine RBC membranes on western blot analysis, whereas anti-MCT2, anti-MCT4, anti-MCT6, and anti-MCT8 antibodies resulted in no signal. No correlation was found between the amount of MCT1 or MCT7 and lactate transport activity, but the ancillary protein CD147 that is needed for the activity of MCT1 had a positive linear correlation with the rate of lactate influx. The apparent Michael is constant for the lactate influx in canine RBCs was 8.8 +/- 0.9mM. Results of in vitro incubation studies revealed that at lactate concentrations of 5 to 15mM, equilibrium of lactate was rapidly obtained between plasma and RBCs. CONCLUSIONS AND CLINICAL RELEVANCE These results indicated that at least half of the lactate transport in canine RBCs occurs via MCT1, whereas MCT7 may be responsible for the rest, although an additional transporter was not ruled out. For practical purposes, the rapid equilibration of lactate between plasma and RBCs indicated that blood lactate concentrations may be estimated from plasma lactate concentrations.

Seasonal changes in reindeer physiology

The seasonal changes in the photoperiod, temperature and availability of food need to be converted to hormonal signals in order to induce adaptations in the physiology of the reindeer. The most reliable of the seasonal changes in the environment is the photoperiod, which affects the reindeer physiology through pineal gland and its hormone, melatonin. Usually there are large diurnal changes in the concentration of melatonin, but in the reindeer the daily rhythm disappears during the arctic summer to return again in the autumn. Seasonal changes in melatonin secretion are involved in the regulation of reproduction, the growth of pelage, thermogenesis, body mass and immune function. Melatonin may exert its effects through gene activation, but the mechanisms are not completely understood. Other hormones that show seasonality are thyroid hormones, insulin and leptin. Thus the observed physiological changes are a result of actions of several hormones. Appetite, energy production and thermogenesis are all vital for survival. During winter, when energy balance is negative, the reindeer uses mainly body fat for energy production. The use of fat stores is economical as the rate of lipolysis is controlled and the use of fatty acids in tissues such as muscle decreases. Only in severe starvation the rate of lipolysis increases enough to give rise to accumulation of ketone bodies. The protein mass is maintained and only in starved individuals muscle protein is used for energy production. The winter feed of the reindeer, the lichens, is poor in nitrogen and the nitrogen balance during winter is strongly negative. Reindeer responds to limited availability of nitrogen by increasing the recycling of urea into rumen. In general the adaptation of reindeer physiology enables the reindeer to survive the winter and although several aspects are known many others require further studies. Abstract in Finnish / Tiivistelma: Valaistus, lampotila ja ravinnon saatavuus vaihtelevat vuodenajn mukaan. Jotta nama muutokset voisivat saada aikaan adaptiivisia muutoksia porossa, ne taytyy muutta hormonisignaaleiksi. Luotettavin naista edella mainituista ympariston vuodenaikaismuutoksista on valo, joka vaikuttaa poron elintoimintoihin kapylisakkeen ja sen erittaman hormonin, melatoniinin, valityksella. Melatoniinin plasmapitoisuuksissa on havaittavissa selkea vuorokausirytmi, joka porolla haviaa kesalla ja alkaa uudestaan syksylla. Melatoniini-hormonin vuodenaikaisvaihtelut ovat mukana saatelemassa lisaantymista, talvikarvan kasvua, lammontuottoa, elopainoa ja immuunitoimintoja. Melatoniini vaikuttaa geeniaktivaation kautta mekanismeilla, joita ei viela tarkkaan tunneta. Muita hormoneja, joiden erityksessa on havaittu vuodenaikaisvaihtelua, ovat kilpirauhashormonit, insuliini ja leptiini. Havaitut muutokset ovat ilmeisesti usean hormonin yhteisvaikutuksen aiheuttamia. Ruokahalu seka energian- etta lammontuotto ovat keskeisia hengissa sailymisen kannalta. Talvella poron energiatase on negatiivinen ja se kayttaa lahinna varastoimiaan rasvoja energian tuottoon. Rasvojen kaytto on ekonomista, silla rasvojen hajoaminen, lipolyysi, on saadeltya ja rasvahappojen kaytto lihaksissa vahenee talvella. Vasta vakavasti nalkiintyneissa poroissa lipolyysi aktivoituu siten, etta myos ketoaineita alkaa kertya vereen. Valkuaisaineiden maara vahenee vahemman kuin rasvojen ja ainoastaan nalkiintyneet porot kayttavat lihasten valkuaisaineita energiantuottoon. Poron talviravinnossa, jakalassa, on vain vahan typpea, joten talvisin typpitasapaino on voimakkaasti negatiivinen. Poro reagoi tahan vahaiseen typpimaaraan lisaamalla urean kierratysta potsiin. Kokonaisuudessaan poron elintoimintojen sopeutuminen auttaa poroa selviytymaan talven yli. Vaikka adaptaatiosta on joiltakin osin kertynyt runsaasti tietoa, on siina myos paljon selvitettavaa.