Evaluation of glucose tolerance and intestinal luminal membrane glucose transporter function in horses with equine motor neuron disease

Eosinophilic Enteritis in Horses with Motor Neuron Disease

BACKGROUND

Equine motor neuron disease (EMND) is a neuromuscular disorder that affects adult horses. Although EMND has been linked to vitamin E deficiency, its etiopathogenesis is poorly understood.

OBJECTIVES

To describe clinical features, laboratory results, and postmortem findings in a series of young horses with motor neuron disease (MND).

ANIMALS

A herd of 15 young Andalusian horses with weakness, weight loss, muscle atrophy, and muscle fasciculations related to restricted intake of green forage.

METHODS

A case series is presented in which horses were subjected to a clinical examination and plasma vitamin E measurement. Five severely affected horses were euthanized for detailed postmortem examination. Muscle specimens were taken from the M. sacrocaudalis dorsalis medialis and the M. gluteus medius for histopathologic and morphometric evaluation.

RESULTS

MND was diagnosed in 5 horses based on clinical signs, low serum levels of vitamin E (0.11 ± 0.05 mg/dL; normal range,: 0.3-1.5 mg/dL), changes in muscle histopathology (neurogenic atrophy), and spinal cord lesions (neuronal chromatolysis in ventral horns). An unexpected postmortem finding was the presence of intestinal inflammation (catarrhal enteritis, edema, and eosinophilic infiltrate) associated with the presence of giant ciliated protozoa in all of the horses.

CONCLUSIONS

Although a mechanistic link could not be established, it is hypothesized that intestinal inflammation may have been involved in the decreased absorption of vitamin E, thus favoring the development of MND.

The potential and limitations of quantitative electromyography in equine medicine

This review discusses the scope of using (quantitative) electromyography (EMG) in diagnosing myopathies and neuropathies in equine patients. In human medicine, many EMG methods are available for the diagnosis, pathophysiological description and evaluation, monitoring, or rehabilitation of patients, and some of these techniques have also been applied to horses. EMG results are usually combined with other neurophysiological data, ultrasound, histochemistry, biochemistry of muscle biopsies, and clinical signs in order to provide a complete picture of the condition and its clinical course. EMG technology is commonly used in human medicine and has been subject to constant development and refinement since its introduction in 1929, but the usefulness of the technique in equine medicine is not yet widely acknowledged. The possibilities and limitations of some EMG applications for equine use are discussed.

Expression and regulation of facilitative glucose transporters in equine insulin-sensitive tissue: from physiology to pathology

Glucose uptake is the rate-limiting step in glucose utilization in mammalians and is tightly regulated by a family of specialized proteins, called the facilitated glucose transporters (GLUTs/SLC2). GLUT4, the major isoform in insulin-responsive tissue, translocates from an intracellular pool to the cell surface and as such determines insulin-stimulated glucose uptake. However, despite intensive research over 50 years, the insulin-dependent and -independent pathways that mediate GLUT4 translocation are not fully elucidated in any species. Insulin resistance (IR) is one of the hallmarks of equine metabolic syndrome and is the most common metabolic predisposition for laminitis in horses. IR is characterized by the impaired ability of insulin to stimulate glucose disposal into insulin-sensitive tissues. Similar to other species, the functional capability of the insulin-responsive GLUTs is impaired in muscle and adipose tissue during IR in horses. However, the molecular mechanisms of altered glucose transport remain elusive in all species, and there is still much to learn about the physiological and pathophysiological functions of the GLUT family members, especially in regard to class III. Since GLUTs are key regulators of whole-body glucose homeostasis, they have received considerable attention as potential therapeutic targets to treat metabolic disorders in human and equine patients.

Gluten-dependent antibodies in horses with inflammatory small bowel disease (ISBD)

BACKGROUND

Equine inflammatory small bowel disease (ISBD) is an idiopathic pathologic condition seeming to increase in prevalence.

OBJECTIVE

To investigate the potential role of gluten in equine ISBD.

ANIMALS & METHODS

Antibodies known to be important in the diagnosis of human coeliac disease (CD): IgA antibodies to human recombinant and guinea pig tissue-transglutaminase (TGA), native gliadin (AGA), deamidated-gliadin-peptides (DGPA), and primate and equine endomysium (EMA) were assessed in blood samples from three different groups of horses: ISBD affected (n = 12) on a gluten-rich diet and controls either on gluten-rich (n = 22) or gluten-poor (n = 25) diets. Significant differences (p < 0.05) between groups were assessed using the Wilcoxon test.

RESULTS

Both ISBD-affected horses and gluten-rich controls had significantly (p < 0.0004) higher hrTGA titers than gluten-poor controls. However, ISBD horses did not show significantly increased levels of any of the CD related antibodies when compared to gluten-rich controls. Nevertheless, markedly increased antibody levels (TGA, EMA and DGPA) were found in one of the ISBD horses. The introduction of a gluten-free ration in this 14-year-old warmblood stallion resulted after 6 months in the reduction of antibody levels and clinical recovery associated with improved duodenal histopathology.

CONCLUSION

To the best of our knowledge, this is the first study assessing gluten-related antibodies in horses and results suggest a potential pathogenic role of gluten in at least some cases of equine ISBD. Clinical importance and impact for human medicine: Given serology and concurrent clinical findings, this study warrants further investigations into the immunologic basis of possible gluten-sensitive enteropathy in horses and analogy with human disease.

The role of quantitative electromyography (EMG) in horses suspected of acute and chronic grass sickness

REASONS FOR PERFORMING THE STUDY

Clinical evidence of motor neuron involvement in equine grass sickness (EGS) has not been reported.

HYPOTHESIS

Quantitative electromyography (EMG) analysis can elucidate subtle changes of the lower motor neuron system present in horses with EGS, performed ante mortem.

METHODS

Fourteen horses diagnosed clinically with acute, subacute or chronic EGS were examined and quantitative EMG performed. Previously published data on healthy horses and horses with proven lower motor neuron disease (LMND) were used as controls. In 8 horses post mortem examination was performed, and in 7 muscle biopsies of the lateral vastus muscle underwent histopathology and morphometry.

RESULTS

Clinical electrophysiological evidence of neuropathy was present in 12 horses. Analysis of data from the first 4 horses resulted in 95% confidence intervals (CI) of nontransformed data for motor unit action potential (MUP) duration in subclavian, triceps and lateral vastus muscle of 11.0-13.7, 14.8-20.3 and 12.2-17.2 msecs, respectively, and for MUP amplitude 291-453, 1026-1892 and 957-1736 microV, respectively. For number of phases the 95% CI was 3.6-4.4, 2.9-3.6 and 2.9-3.4, respectively, and for number of turns 5.0-6.5, 4.3-5.3 and 3.7-4.6, respectively. No changes in duration of insertional activity were measured. Pathological spontaneous activity was observed in all horses. EGS as evidenced by degenerative changes in the autonomic ganglia in combination with minor degenerative changes of the spinal lower motor neurons was observed on post mortem examination in all 8 available autopsies. In muscle biopsies of 4 out of 7 horses changes consistent with slight neurogenic atrophy were found.

CONCLUSIONS AND POTENTIAL RELEVANCE

EMG results demonstrated the presence of a neuropathy of skeletal muscles in all horses suspected to have EGS. The combination of clinical and electrophysiological evidence may aid differential diagnosis of neurogenic disease in cases of weight loss and colic.

The role of electromyography in clinical diagnosis of neuromuscular locomotor problems in the horse

REASONS FOR PERFORMING STUDY

Systematically performed EMG needle examination of muscles provides essential information about the functional aspects of the motor unit. However, clinical studies in which information is given on the diagnostic and discriminative values of electromyography (EMG) in the horse are scarce.

OBJECTIVES

To determine to what extent inclusion of EMG analysis in clinical examination contributes to determination of type and localisation of abnormality.

METHODS

EMG analysis, complete clinical examination and diagnosis of 108 horses (mean +/- s.d. age 75 +/- 3.8 years; bodyweight 548 +/- 86 kg; height 1.67 +/- 0.07 m) were performed, and results without and with EMG analysis compared.

RESULTS

Without EMG, myopathy and neuropathy were diagnosed in 20 and 58 horses, respectively, and with EMG in 17 and 82 horses. EMG changed localisation in myopathy and neuropathy in 12 and 37% of cases, respectively. Lesions in the C1-T2, T2-L3 and L3-S3 segments were, respectively, diagnosed without EMG in 7, 11 and 30%, and with EMG in 27, 7 and 17% of cases. Where no clinical diagnosis could be made prior to EMG, many patients appeared to be suffering from localised cervical lesions (29%) or generalised neuropathy (54%).

CONCLUSIONS AND POTENTIAL RELEVANCE

The assistance of EMG in discriminating between normal, neuropathy and myopathy, and in locating pathology, contributes to diagnosis of neuromuscular problems.

(Over)training effects on quantitative electromyography and muscle enzyme activities in standardbred horses

Too intensive training may lead to overreaching or overtraining. To study whether quantitative needle electromyography (QEMG) is more sensitive to detect training (mal)adaptation than muscle enzyme activities, 12 standardbred geldings trained for 32 wk in age-, breed-, and sex-matched fixed pairs. After a habituation and normal training (NT) phase ( phases 1 and 2, 4 and 18 wk, respectively), with increasing intensity and duration and frequency of training sessions, an intensified training (IT) group ( phase 3, 6 wk) and a control group (which continued training as in the last week of phase 2) were formed. Thereafter, all horses entered a reduced training phase ( phase 4, 4 wk). One hour before a standardized exercise test (SET; treadmill), QEMG analysis and biochemical enzyme activity were performed in muscle or in biopsies from vastus lateralis and pectoralis descendens muscle in order to identify causes of changes in exercise performance and eventual (mal)adaptation in skeletal muscle. NT resulted in a significant adaptation of QEMG parameters, whereas in muscle biopsies hexokinase activity was significantly decreased. Compared with NT controls, IT induced a stronger adaptation (e.g., higher amplitude, shorter duration, and fewer turns) in QEMG variables resembling potentially synchronization of individual motor unit fiber action potentials. Despite a 19% decrease in performance of the SET after IT, enzyme activities of 3-hydroxyacyl dehydrogenase and citrate synthase displayed similar increases in control and IT animals. We conclude that 1) QEMG analysis is a more sensitive tool to monitor training adaptation than muscle enzyme activities but does not discriminate between overreaching and normal training adaptations at this training level and 2) the decreased performance as noted in this study after IT originates most likely from a central (brain) rather than peripheral level.

Horses on pasture may be affected by equine motor neuron disease

REASONS FOR PERFORMING STUDY

Equine motor neuron disease (EMND) was diagnosed in 3 horses maintained on lush, grass-based pasture. This contrasted with North American studies which identified limited or no access to green herbage as an important risk factor for EMND.

HYPOTHESIS

Grazing horses that have an apparently adequate intake of pasture herbage to meet normal equine vitamin E requirements can develop EMND.

METHODS

Owners of 32 European horses diagnosed with EMND completed a questionnaire regarding intrinsic, managemental, nutritional and environmental factors that could potentially be risk factors for EMND, and also regarding clinical signs, treatments and case outcome. Plasma/serum vitamin E data for these horses were supplied by the veterinarians. No control population was studied.

RESULTS

Thirteen of 32 horses (termed the 'grazing' group) had part- or full-time access to grass-based pasture at the onset of EMND (median duration at pasture 12 h/day, range 3-24 h). Five of these horses were at pasture for at least 235 h/day at the onset of EMND, 2 of which were at pasture for at least 23.5 h/day throughout the year. Despite grazing, all these horses had a low vitamin E status. The remaining 19 horses resembled those cases reported from North America, in that they had no or limited access to pasture.

CONCLUSIONS AND POTENTIAL RELEVANCE

A diagnosis of EMND should not be discounted on the basis that a horse has access, even full-time, to lush grass-based pasture. Inadequate vitamin E intake was probably not the sole cause of either the EMND or the low vitamin E status in the grazing horses; the latter was probably the result of abnormal bioavailability or excessive utilisation of vitamin E.

Evaluation of glucose metabolism in three horses with lower motor neuron degeneration

OBJECTIVES

To determine whether increased glucose metabolism is the potential cause of the decreased plasma glucose curve determined after oral glucose tolerance testing in horses with lower motor neuron degeneration.

ANIMALS

3 horses with signs suggestive of lower motor neuron degeneration, 1 horse with malignant melanoma with multiple metastases, and an obese but otherwise healthy horse. Procedures-Glucose metabolism was assessed by use of the hyperglycemic clamp and euglycemic hyperinsulinemic clamp techniques.

RESULTS

Mean rate of glucose metabolism of horses with lower motor neuron degeneration was significantly greater (mean, 3.7 times greater than control horses; range, 2.1 to 4.8 times greater) than that reported in 5 healthy control horses (41 +/- 13 micromol/kg/min vs 11 +/- 4.5 micromol/kg/min, respectively). In addition, one of the affected horses, an 8-year-old warmblood gelding, had a 5.6-times increased sensitivity to exogenously administered insulin, compared with that reported in 5 healthy control horses. Pancreatic insulin secretion was not insufficient in horses with lower motor neuron degeneration. Findings in the 2 diseased control horses were unremarkable.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased glucose metabolism in horses with lower motor neuron degeneration may be the cause of the decreased plasma glucose curve detected after oral glucose tolerance testing. This finding could aid in developing supportive treatments with respect to adequate glucose and vitamin E supplementation.