Exercise-associated hyponatremia in Alaskan sled dogs: urinary and hormonal responses

Subclinical hypernatraemia in a population of endurance racing sled dogs

Electrolyte disturbances occur in both human and veterinary endurance athletes; however, hypernatraemia is poorly documented in dogs. To further explore electrolyte changes in canine endurance athletes, we collected blood from two teams of dogs (n=16) participating in the mid-distance (336 km) CanAm race. Serum samples were collected 36 hours before the start and within 20 minutes of race completion. Serum was similarly collected from 18 dogs withdrawn after completing 264 km. Biochemical profiles and aldosterone assays were performed. Mean serum sodium (>155 mEq/l) and corrected chloride concentrations were significantly increased (P<0.01) from baseline in finishing and withdrawn dogs; however, unlike sodium, corrected chloride concentrations remained within the reference interval. Serum phosphorous, hepatic enzymes, cholesterol, creatinine kinase, blood urea nitrogen, globulin, glucose, and iron concentrations were also significantly increased (P<0.01) compared to baseline in both finishing and withdrawn dogs. Both mean serum aldosterone and urea nitrogen concentrations were significantly increased (P<0.01) from baseline in finishing and withdrawn dogs, with finishers having greater concentrations than withdrawn dogs (P<0.01). Pre-race and matched finishing dog populations were then used for correlation analysis. Serum sodium concentrations were significantly (P<0.01) and strongly correlated with chloride (r=0.92), albumin (r=0.88), total protein (r=0.87), globulin (r=0.81), and potassium (r=0.86). Serum sodium concentrations were not significantly correlated with serum aldosterone concentrations (r=0.04, P=0.87). This study uniquely described subclinical hypernatraemia in the canine endurance athlete. The data lend support of dehydration through free water loss as a cause of hypernatraemia likely compounded by insufficient replenishment by drinking. Elevations in aldosterone concentrations in the face of hypernatraemia may be attributed to concurrent extra-renal hypotonic water losses, counter regulatory hormone influences, or physiological hyperthermia. Such findings demonstrate a degree of clinical tolerance for euvolemic driven hypernatraemia in endurance sled dogs, while highlighting the need for appropriate water supplementation.

Impact of High Temperature on Post-Exercise Albuminuria in Dogs

Simple Summary

The literature suggests that strenuous exercise and exposure to high temperatures may cause physiologic proteinuria, but there are no available data showing the effect of high temperature on the occurrence of post-exercise albuminuria in dogs. The goal of the present study was to assess impact of high temperature on the occurrence of albuminuria. A period of about 30–40 min of intensive exercise at high temperatures did not lead to increased albuminuria. This suggests that there is no need to limit physical activity before urine tests in dogs, even at high temperatures, before a urinalysis.

Abstract

The literature suggests that strenuous exercise and exposure to high temperatures may cause physiologic proteinuria, but to our knowledge there have been no studies that have assessed the effect of high temperatures on the occurrence of post-exercise albuminuria in dogs. The goal of the study was to assess the impact of high temperatures on the occurrence of albuminuria. Thirteen healthy adult dogs—eight female (62%) and five male (38%) had to run 5 km at a temperature of 25 °C in grasslands which took about 30–40 min. Dogs underwent clinical examinations: echocardiography, abdominal ultrasound, blood hematology and biochemistry and urinalysis, including the ratio of albumin to creatinine (UAC). Baseline UAC was on the borderline of statistical significance for female dogs, but not for male dogs, before and after exercise. UAC was 0.31 ± 0.56 mg/mmol for female dogs and 0.36 ± 0.60 mg/mmol in male dogs before exercise. Immediately after exercise, UAC was 0.51 ± 0.58 mg/mmol in female dogs and 0.31 ± 0.40 mg/mmol in male dogs. Thus, a period of about 30–40 min of intensive exercise at high temperatures (25 °C) did not lead to increased albuminuria. This suggests that there is no need to limit the movement activity before urine tests in dogs, even at high temperatures, before urinalysis.

Changes in salivary electrolyte concentrations in mid-distance trained sled dogs during 12 weeks of incremental conditioning

Regular exercise improves the health status of dogs; however, extreme exertion in the absence of adequate fluid and electrolyte replacement may negatively impact health and performance due to dehydration and cardiovascular stress. Unlike humans and horses, dogs thermoregulate predominantly through respiration and salivation, yet there is a dearth of literature defining exercise-induced changes to canine salivary electrolytes. The study objective was to investigate the effects of exercise on salivary electrolyte concentrations, and to determine if adaptations may occur in response to incremental conditioning in client-owned Siberian Huskies. Sixteen dogs were used, with an average age of 4.8 ± 2.5 years and body weight of 24.3 ± 4.3 kg. A 12-week exercise regimen was designed to increase in distance each week, but weather played a role in setting the daily distance. Saliva samples were collected at weeks 0 (pre-run, 5.7 km), 5 (pre-run, 5.7, 39.0 km), and 11 (pre-run, 5.7, 39.0 km). Samples were analyzed for sodium, chloride, potassium, calcium, magnesium, and phosphorous using photometric and indirect ion-selective electrode analysis. When compared across weeks, sodium, chloride, potassium, and calcium concentrations did not differ at any sampling time point; however, phosphorus and magnesium concentrations increased from baseline. Data were then pooled across weeks to evaluate changes due to distance and level of conditioning. Sodium, chloride, and magnesium concentrations increased progressively with distance ran, suggesting that these electrolytes are primarily being lost as exercising dogs salivate. Repletion of these minerals may assist in preventing exercise-induced electrolyte imbalance in physically active dogs.

Haematological and serum biochemical values in Norwegian sled dogs before and after competing in a 600 km race

Background

Long-distance racing is known to cause alterations in haematological and serum biochemical parameters in sled dogs. Given that finishing status reflects the physical condition in dogs completing a race, such variations will mainly be the result of physiological adaption achieved during endurance exercise. However, changes observed in withdrawn dogs may indicate pathological conditions. The aim of this study was to reveal changes in haematological and serum biochemical values in sled dogs participating in a long-distance race, with emphasis on the withdrawn dogs. Sixty-five sled dogs participated in a clinical prospective cohort study: 46 dogs competed in the 600 km race (25 finishing and 21 withdrawn dogs), and 19 dogs served as controls. Blood sampling was performed early in the training season and after the race.

Results

When compared to control dogs, both withdrawn and finishing dogs showed significant increases in neutrophil count, C-reactive protein, blood urea nitrogen and sodium/potassium ratio. Significant decreases were found in erythrocytes and eosinophil cell count, and in haematocrit, haemoglobin, total protein, albumin, globulin, creatinine, potassium and calcium levels. Finishing dogs presented significant increases in white blood cells, large unstained cells, monocyte count and cortisol level compared to control dogs. In contrast, withdrawn dogs had significant elevations in alanine aminotransferase and alkaline phosphatase activity, as well as parameters associated with muscle metabolism, such as aspartate aminotransferase, creatine kinase and phosphorus concentration.

Conclusions

Competing sled dogs experienced minor changes in blood parameters in general, mainly revealing the same pattern among withdrawals and finishers. This might indicate that numerous changes simply reflect physiological adaption due to endurance exercise. However, the serum concentration of muscle enzymes was significantly increased only in the withdrawals, and were well above reference ranges. This reflects muscle degradation, which could be the main cause of performance failure in some of the withdrawals.

Electronic supplementary material

The online version of this article (10.1186/s13028-019-0453-5) contains supplementary material, which is available to authorized users.

Serum Biochemistry and Inflammatory Cytokines in Racing Endurance Sled Dogs With and Without Rhabdomyolysis

Serum muscle enzymes in endurance sled dogs peak within 2–4 days of racing. The object of this study was to compare mid-race serum chemistry profiles, select hormones, markers of inflammation, and the acute phase response in dogs that successfully completed half of the 2015 Yukon Quest sled dog race to their pre-racing samples (n = 14), as well as mid-race samples of successful dogs to those who developed clinical exertional rhabdomyolysis (ER) (n = 5). Concentrations of serum phosphorus in ER dogs were significantly elevated compared to healthy dogs (median 5.5 vs. 4.25 mg/dL, P < 0.01) at mid race. ALT, AST, and CK show a significant increase from pre-race baseline to mid-race chemistries (P < 0.01), with more pronounced increases in dogs with ER compared to healthy racing dogs (CK- median 46,125 vs. 1,743 U/L; P < 0.01). Potassium concentrations were significantly decreased from pre-race baselines in all dogs (median 5.1 vs. 4.5 mEq/L; P < 0.01), and even lower in dogs with ER (median 3.5 mEq/L; P < 0.01) mid-race. No changes in serum pro-inflammatory cytokine concentrations were noted in any groups of dogs. C-reactive protein was elevated in both groups of dogs, but significantly higher in those with ER compared with healthy dogs mid-race (median 308 vs. 164 ug/mL; P < 0.01). Healthy dogs may have CK elevations over 10,000 U/L, and dogs with ER were over 30,000 U/L. Although potassium decreases in healthy endurance sled dogs during racing, it remains in the normal laboratory reference range; however ER dog potassium levels drop further to the point of hypokalemia. Lastly increases in CRP may be reflective of a physiological response to exercise over the course of a race; however high CRP in ER dogs may be capturing an early acute phase response.

Gastritis and Gastric Ulcers in Working Dogs

Gastritis and gastric ulcers are an important cause of morbidity and mortality in canine athletes. Although the majority of scientific work on this condition has been performed in ultraendurance racing sled dogs, this condition has been identified in other canine athletes, including sled dogs competing in shorter events and dogs performing off-leash explosive detection duties. The cause of the syndrome is unknown, but current hypotheses propose a link between exercise-induced hyperthermia and loss of gastric mucosal barrier function as an early event in the pathogenesis. Treatment is focused on prevention of clinical disease using acid secretion inhibitors, such as omeprazole, which has excellent efficacy in controlled clinical studies.

Plasma chemistry before and after two consecutive days of racing in sled dogs: associations between muscle damage and electrolyte status

Exercising long distance endurance sled dogs display plasma biochemistry changes characterised by elevations in creatine kinase (CK) and aspartate aminotransferase (AST), hypoproteinemia, hypoglobulinemia and decreases in sodium and potassium. The aim of this study was to compare resting to day 2 racing plasma biochemistry and associations between electrolytes and markers of muscle damage in well-conditioned sled dogs during a stage-stop race. Blood samples were obtained from 23 dogs prior to the start and on day 2, immediately after racing. Results showed significant decreases in potassium (day 0 – 4.7±0.3 and day 2 – 4.2±0.3 mEq/l), total protein (day 0 – 6.0±0.3 and day 2 – 5.5±0.4 g/dl) and albumin concentrations (day 0 – 3.9±0.2 and day 2 – 3.6±0.3 g/dl). Increases in AST (day 0 – 24±7 and day 2 – 137±97 U/l) and CK activities (day 0 – 129±39 and day 2 – 2,047±2,021 U/l) were also observed. Plasma sodium concentrations were not significantly different after day 2 of racing (day 0 – 153±5.2 and day 2 – 151±4.1). Alterations in plasma electrolytes, and increases in AST, CK, alanine aminotransferase and urea nitrogen were similar to those observed in long distance endurance sled dogs. A strong negative association was observed between plasma potassium and increases in plasma CK activity on day 2 (R2=0.69). The maintenance of sodium concentrations with a concurrent potassium decline, suggests sodium conservation via the renin-angiotensin-aldosterone pathway as previously shown in endurance sled dogs. The negative correlation between muscle damage and plasma potassium warrants further investigation regarding its relationship to rhabdomyolysis.

Serum chemistry and electrolyte alterations in sled dogs before and after a 1600 km race: dietary sodium and hyponatraemia

Sled dogs are known to develop numerous serum biochemical changes due to endurance exercise. Previous studies have suggested that mild hyponatraemia and hypokalaemia can develop during endurance racing. The aim of the present study was to determine if serum biochemical alterations are similar to previous reports, and if electrolyte alterations are still present with present feeding practices utilised by mushers. Serum chemistries were obtained from 26 Alaskan Huskies belonging to 3 different teams, before and after a 1600 km race. Meals and snacks were analysed via calculation to determine daily macronutrient and electrolyte intake. Numerous biochemical alterations were observed including significant differences in serum total protein, albumin, globulin, aspartate aminotransferase, creatine kinase, TAG, NEFA and urea nitrogen (P < 0·05). Serum electrolyte status revealed a mild, yet significant decrease in serum sodium (P = 0·002); and serum potassium was not significantly different (P = 0·566). Further examination of the sodium intake across the three teams revealed two teams with an average daily intake of approximately 8·5 g/dog/d (700 mg/4184 kJ) and the other team consuming 11·1 g/dog/d (1200 mg/4184 kJ). Regression analysis shows a significant modest positive correlation between serum sodium decrease and sodium intake per metabolic body weight of the dogs, as well as a modest positive correlation between sodium intake and serum potassium implicating the renin-angiotensin aldosterone system as a major factor involved in sodium and potassium homoeostasis. These findings suggest that consumption of approximately 0·9 g/kg(0·75) (1·2 g/4184 kJ) of sodium per d may prevent exercise-induced decreases in sodium and potassium.

Influence of endurance exercise on serum concentrations of iron and acute phase proteins in racing sled dogs

OBJECTIVE

To determine effects of long-distance racing exercise on iron status in endurance racing sled dogs, with or without anemia.

DESIGN

Prospective cohort study.

ANIMALS

114 dogs that participated in the 2007 Iditarod Trail Sled Dog Race (59 and 55 dogs that did or did not complete the race, respectively).

PROCEDURES

Stored serum samples obtained from 85 endurance-racing sled dogs that were expected to participate in the race were used to establish study reference intervals and prerace group values for iron-related variables. Blood samples collected from 114 study dogs before (ie, baseline) and after participation in the race were used to determine PCV and serum total protein concentrations before and after racing and assess iron-related variables after racing.

RESULTS

Mean values for PCV and serum total protein concentration were decreased after racing, compared with baseline values in the same dogs. Mean serum iron concentration was low, and mean serum ceruloplasmin and C-reactive protein (CRP) concentrations were high in dogs after racing, compared with prerace group values. Mean serum ferritin concentration was high in dogs that did not complete the race, compared with the prerace group value and that of dogs that finished the race; 4 of 113 (3.5%) study dogs had low ferritin concentrations (< 73 ng/mL) after racing, suggestive of possible iron deficiency.

CONCLUSIONS AND CLINICAL RELEVANCE

Decreased PCV and serum total protein concentrations were consistently detected, whereas iron deficiency appeared to be uncommon, in study dogs after race participation. High serum concentrations of ceruloplasmin and CRP after racing suggested that changes indicative of iron deficiency may be masked by inflammation. Alternatively, changes in serum iron and CRP concentrations may reflect a physiologic response.

Evaluation of exercise-induced changes in concentrations of C-reactive protein and serum biochemical values in sled dogs completing a long-distance endurance race

OBJECTIVE

To determine whether long-distance endurance exercise in sled dogs causes increases in serum concentrations of C-reactive protein (CRP) and whether such increases are correlated with other markers of the exercise-induced acute-phase response.

ANIMALS

25 sled dogs.

PROCEDURES

Serum was obtained from 25 sled dogs approximately 48 hours before and immediately after completing a race of 557 km. Serum was analyzed to determine concentrations of CRP and interleukin (IL)-6, and serum biochemical analysis (and iron homeostasis analysis) also was performed.

RESULTS

CRP concentrations increased significantly from a mean±SD concentration of 22.4±16.3 microg/mL before racing to a mean of 263.3±103.8 microg/mL immediately after racing Serum IL-6 concentrations were unchanged; however, there was a modest but significant correlation (r=0.50) between the increase in CRP concentration and an overall decrease in serum albumin concentration, which suggested an inverse relationship between hepatic synthesis of the 2 proteins. Differences in CRP concentrations among teams of dogs revealed that concentrations before racing may be influenced by previous episodes of exercise. Serum iron concentration had only a mild decrease, which may have been attributable to iron-rich diets consumed by the dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

CRP concentrations may serve as a potential marker for exercise-induced inflammation. The exact amount of exercise required to induce such a response is unknown, but dogs apparently have a more robust acute-phase response than do humans. Clinical evaluation of CRP concentrations must account for physical activity when those concentrations are used as a potential marker for systemic inflammation.

Assessment of serum antibody titers against canine distemper virus, canine adenovirus type II, and canine parvovirus in Alaskan sled dogs before and after a long-distance race

OBJECTIVE

To determine serum antibody titers against canine distemper virus (CDV), canine adenovirus type II (CAV-2), and canine parvovirus (CPV) in trained sled dogs prior to and after completion of a long-distance race.

DESIGN

Prospective cohort study.

ANIMALS

195 Alaskan sled dogs (from 18 kennels) that participated in the 2006 Iditarod Trail Race.

PROCEDURES

All 1,323 dogs participating in the race had been vaccinated against the 3 viruses at 19 to 286 days prior to initial blood sample collection (obtained within the month preceding the race). Within 12 hours of race completion, blood samples were collected from 195 dogs (convenience sample) and matched with each dog's prerace sample. Serum antibody titers (90% confidence intervals [CIs]) were determined via serum neutralization assays.

RESULTS

After racing, geometric mean titers against CDV and CPV were significantly higher (2,495 [90% CI, 321 to 16,384] and 6,323 [90% CI, 512 to 32,768], respectively) than prerace values (82 [90% CI, 11 to 362] and 166 [90% CI, 32 to 1,024], respectively). Sixty-one of 194 (31.4%) dogs had > or = 4-fold increases in anti-CPV antibody titers after racing. Prerace serum antibody titers against CDV, CPV, and CAV-2 varied significantly by sled team but were not associated with time since vaccination.

CONCLUSIONS AND CLINICAL RELEVANCE

Postrace increases in serum anti-CDV and anti-CPV antibody titer might reflect exposure of dogs to these agents immediately before or during racing. Dogs had no clinical signs of CDV-, CAV-2-, or CPV-associated disease; therefore, the clinical importance of these titer changes is uncertain.

Serum chemistry alterations in Alaskan sled dogs during five successive days of prolonged endurance exercise

OBJECTIVE

To determine the impact of successive days of endurance exercise on select serum chemistry values in conditioned Alaskan sled dogs.

DESIGN

Prospective cohort study.

ANIMALS

10 conditioned Alaskan sled dogs.

PROCEDURES

All dogs ran 160 km/d for 5 consecutive days. Serum was obtained prior to exercise and immediately after each exercise run; all samples were obtained before dogs were fed. Serum electrolyte, mineral, protein, total bilirubin, urea nitrogen, creatinine, and cardiac troponin-I concentrations and serum alkaline phosphatase, alanine aminotransferase, creatine kinase, and aspartate aminotransferase activities were measured. Data were analyzed by means of analysis of covariance for a randomized complete block design with dog as a blocking variable, time as a covariate, and distance run as the treatment of interest. Least square mean values were compared with values obtained prior to exercise, and linear and quadratic contrasts were examined.

RESULTS

Serum globulin concentration was low prior to exercise (mean +/- SD, 2.2 +/- 0.3g/dL) and progressively decreased as exercise continued. Exercise was associated with increases in serum chloride, urea nitrogen, and cardiac troponin-I concentrations and serum alanine aminotransferase, creatine kinase, and aspartate aminotransferase activities and with progressive decreases in serum potassium, total protein, and albumin concentrations.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that multiple successive days of endurance exercise resulted in mild aberrations in serum chemistry variables in conditioned sled dogs. Changes likely reflected the metabolic stresses of prolonged endurance exercise as well as dietary composition. Hypoglobulinemia in resting, conditioned sled dogs may reflect the immunosuppressive or catabolic effects of intense endurance training.

Fluid and electrolyte shifts during and after Agility competitions in dogs

This research assesses the relative contribution of splenic contraction and fluid shifts out of the vascular compartment to the increases in packed cell volume associated with Agility exercises. It also aims to evaluate the changes in the concentrations of electrolytes and markers of hydration state. Fifteen dogs of both sexes were subjected to an Agility exercise of an approximate duration of 100 s. Blood samples were obtained within the first 30 s after competition and at 5, 15, and 30 min of recuperation. Resting values were established previously. The following parameters were determined: packed cell volume (PCV), plasma lactate (LA), total plasma protein (TPP), albumin (ALB), urea (BUN), creatinine (CREA), chloride (Cl), calcium (Ca), phosphorus (P), sodium (Na) and potassium (K). Changes in plasma volume (PV), total RBC volume (V(RBC)) and blood volume (BV) were calculated immediately after exercise and at 30 minutes of recovery. It was found that during Agility competition, BV, V(RBC) and PV increased 12, 21 and 4% respectively, indicating that the spleen contraction was the main determinant on the increase of BV. In comparison with resting values, BV decreased after recuperation (-5%), due to the recapture of erythrocytes by the splenic reserve (V(RBC), -12%). Additionally, Agility exercise induced increases in plasma Cl and LA, with significant reductions of ALB, Ca and P and absence of modifications in Na, K, BUN and CREA concentrations.

Effect of strenuous exercise on urine concentrations of homovanillic acid, cortisol, and vanillylmandelic acid in sled dogs

OBJECTIVE

To determine whether prolonged exercise by conditioned sled dogs affects urine concentrations of homovanillic acid (a metabolite of dopamine), vanillylmandelic acid (a metabolite of norepinephrine and epinephrine), and cortisol.

ANIMALS

24 conditioned Alaskan sled dogs (2 to 8.5 years old) that were in training for a multiday endurance race.

PROCEDURES

Voided urine samples were collected from 4 groups of dogs (randomly selected from 54 dogs) after no exercise (control group; n = 6 dogs), completion of a 160km run (group A; 3), completion of a 420-km run (group B; 7), and completion of a 560-km run (group C; 6). Urine cortisol concentrations were determined by use of an immunoassay technique; urine vanillylmandelic acid and homovanillic acid concentrations were measured via high-performance liquid chromatography.

RESULTS

Compared with the control group, urine cortisol concentration in groups A, B, and C was significantly different (5.33 x 10(4) +/- 2.62 x 10(4) microg/dL vs 1.04 x 10(4) +/- 2.31 x 10(5) microg/dL, 8.88 x 10(4) +/- 5.49 x 10(4) microg/dL, and 6.31 x 10(4) +/- 5.09 x 10(4) microg/dL, respectively). Urine homovanillic acid concentration did not differ among the 4 groups. Vanillylmandelic acid was not detected in any urine samples.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that prolonged exercise by sled dogs did not affect urine homovanillic acid concentration but did increase urinary cortisol secretion, which is indicative of adrenocortical stimulation. The apparent lack of vanillylmandelic acid in voided urine samples requires further investigation.

Enteral fluid therapy in large animals

Enteral fluids administered alone, or in conjunction with intravenous fluids, are reported to be useful for the treatment of dehydration and electrolyte loss associated with diarrhoea in a number of species, following exercise in horses and for feed impaction of the large intestine of horses. Enteral fluids are suitable for treatment of mild to moderately dehydrated patients with some intact intestinal epithelium and motile small intestine. In patients that will drink voluntarily or tolerate nasal intubation the use of enteral fluids may avoid the complications associated with intravenous fluid administration. However the labour costs associated with repeated nasal intubation in intensively managed patients requiring large volumes of fluids may make the use of enteral fluids less economical than intravenous fluid administration. Enteral fluid use alone is contraindicated in patients that are severely dehydrated and/or in hypovolaemic shock, however, if used in conjunction with intravenous fluids, the effects of villous atrophy and malnutrition may be ameliorated and the duration of hospitalisation shortened. There is a variety of commercially available enteral fluids available to veterinary practitioners. While the key components of these fluids are sodium, chloride and carbohydrates, the amounts of ions and other ingredients such as potassium, alkalising agents, amino acids and shortchain fatty acids may vary. The species of the animal, the underlying condition, and the constituents of the fluid, should influence the choice of an enteral fluid.

Vitamin E and exertional rhabdomyolysis during endurance sled dog racing

Exertional rhabdomyolysis (ER) is common in sled dogs, animals with high energy expenditures that consume high fat (60% of ingested calories) diets. Associations between pre-race plasma [vitamin E] and total antioxidant status (TAS) and risk of developing ER were examined in dogs competing in the 1998 Iditarod race. Pre-race blood samples were collected from 750 dogs and a second sample was collected from 158 dogs withdrawn from the race at various times. Plasma creatine kinase activity was used to identify withdrawn dogs with ER. There was no association between pre-race plasma [vitamin E] and risk of development of ER. Dogs that developed ER started the race with higher TAS, but when withdrawn, had lower TAS than unaffected dogs and had similar pre-race [vitamin E] but higher [vitamin E] at time of withdrawal. Hence, the risk of ER in sled dogs is not affected by plasma [vitamin E] before the race.

Oxidant stress in sled dogs subjected to repetitive endurance exercise

OBJECTIVE

To determine whether repetitive endurance exercise in sled dogs was associated with substantial lipid peroxidation, decreases in antioxidant capacity of the serum, and skeletal muscle damage.

ANIMALS

24 lightly trained sled dogs.

PROCEDURE

16 dogs completed a 58-km run on each of 3 consecutive days; the other 8 dogs (control) did not exercise during the study. Blood samples were collected before the first exercise run and after the first and third exercise runs. Plasma isoprostane and serum vitamin E concentrations, total antioxidant status of plasma, and serum creatine kinase activity were measured.

RESULTS

Plasma isoprostane concentrations in dogs in the exercise group were significantly increased after the first exercise run and further significantly increased after the third exercise run. Serum vitamin E concentration was significantly decreased after the first exercise run in dogs in the exercise group, and this change persisted after the third exercise run. There was a significant linear relationship between plasma isoprostane concentration and the logarithm of serum creatine kinase activity (adjusted ? = 0.84).

CONCLUSIONS AND CLINICAL RELEVANCE

Results demonstrate that repetitive endurance exercise in dogs is associated with lipid peroxidation and a reduction in plasma antioxidant concentrations. We interpret these results as indicating that the antioxidant mechanisms of minimally trained dogs may, in some instances, be inadequate to meet the antioxidant requirements of repetitive endurance exercise.