Valberg S J, Macleay J M, Billstrom J A, Hower-Moritz M A, Mickelson J R
Department of Clinical and Population Sciences, University of Minnesota, St Paul 55108, USA.
Equine Vet J. 1999 Jan;31(1):43-7. doi: 10.1111/j.2042-3306.1999.tb03789.x.
Polysaccharide storage myopathy (PSSM) is a distinct cause of exertional rhabdomyolysis in Quarter Horses that results in glycogen and abnormal polysaccharide accumulation. The purpose of this study was to determine if excessive glycogen storage in PSSM is due to a glycolytic defect that impairs utilisation of this substrate during exercise. Muscle biopsies, blood lactates and serum CK were obtained 1) at rest from 5 PSSM Quarter Horses, 4 normal Quarter Horses (QH controls) and 6 Thoroughbreds with recurrent exertional rhabdomyolysis (TB RER) and 2) after a maximal treadmill exercise test in PSSM and QH controls. In addition, 3 PSSM horses performed a submaximal exercise test. At rest, muscle glycogen concentrations were 2.4x and 1.9x higher in PSSM vs. QH controls or TB RER, respectively. Muscle lactates at rest were similar between PSSM and QH controls but significantly higher in PSSM vs. TB RER. Muscle glucose-6-phosphate concentrations were also higher in PSSM horses than controls combined. During maximal exercise, mean muscle glycogen concentrations declined 2.7x more and mean lactate increased 2x more in PSSM vs. QH controls; however, differences were not statistically significant. Blood lactate concentrations after maximal exercise did not reflect generally higher muscle lactate in PSSM vs. QH controls. No change in blood lactate concentrations occurred in PSSM horses with submaximal exercise. Serum CK activity increased significantly 4 h after maximal and submaximal exercise and was significantly higher in PSSM vs. QH controls. These results show that during maximal exercise, PSSM horses utilised muscle glycogen and produce lactic acid via a functional glycolytic pathway and that during submaximal exercise oxidative metabolism was unimpaired. The excessive glycogen storage and formation of abnormal polysaccharide in PSSM horses therefore appear to reflect increased glycogen synthesis rather than decreased utilisation. The specific subset of horses with exertional rhabdomyolysis due to PSSM would likely benefit clinically from a diet low in soluble carbohydrates like grain with fat added as well as gradually increasing daily exercise to reduce excessive glycogen accumulation and enhance utilisation.
多糖贮积性肌病（PSSM）是导致夸特马运动性横纹肌溶解的一个独特病因，会导致糖原和异常多糖蓄积。本研究的目的是确定PSSM中糖原过度贮积是否由于糖酵解缺陷导致运动期间该底物利用受损。在以下情况下采集肌肉活检样本、血乳酸和血清肌酸激酶：1）5匹患有PSSM的夸特马、4匹正常夸特马（QH对照）和6匹患有复发性运动性横纹肌溶解的纯种马（TB RER）在静息状态下；2）患有PSSM的马和QH对照在进行最大强度跑步机运动试验后。此外，3匹患有PSSM的马进行了次最大强度运动试验。静息时，与QH对照或TB RER相比，PSSM马匹的肌肉糖原浓度分别高2.4倍和1.9倍。静息时，PSSM马匹和QH对照的肌肉乳酸水平相似，但与TB RER相比，PSSM马匹的肌肉乳酸水平显著更高。PSSM马匹的肌肉葡萄糖-6-磷酸浓度也高于合并后的对照。在最大强度运动期间，与QH对照相比，PSSM马匹的平均肌肉糖原浓度下降幅度多2.7倍，平均乳酸增加幅度多2倍；然而，差异无统计学意义。最大强度运动后血乳酸浓度并未反映出PSSM马匹的肌肉乳酸水平普遍高于QH对照。次最大强度运动后，PSSM马匹的血乳酸浓度没有变化。最大强度和次最大强度运动后4小时，血清肌酸激酶活性显著增加，且PSSM马匹的血清肌酸激酶活性显著高于QH对照。这些结果表明，在最大强度运动期间，PSSM马匹通过功能性糖酵解途径利用肌肉糖原并产生乳酸，且在次最大强度运动期间氧化代谢未受损。因此，PSSM马匹中糖原过度贮积和异常多糖形成似乎反映了糖原合成增加而非利用减少。因PSSM导致运动性横纹肌溶解的特定马群可能在临床上受益于低可溶性碳水化合物（如谷物）并添加脂肪的饮食，以及逐渐增加每日运动量以减少过多糖原蓄积并提高利用率。
