Acute altitude exposure (3800 meters) and metabolic capacity in the middlegluteal muscle of equids

Even relatively short exposure to high altitude can produce changes in the metabolic capacity of muscle. This study examined the changes in citrate sy nthase (CS), beta-hydroxyacyl-CoA-dehydrogenase (HOAD), lactate dehydrogena se (LDH) and total protein (TP) activity of skeletal muscle in equids after acute high altitude exposure (3800 m), The middle gluteal muscles of train ed equids (one Quarter Horse. one Shetland pony, and four Arabians) were sa mpled before altitude exposure (225 m) and after nine days of sub-maximal e xercise at altitude (3800 m). Muscle biopsies were take from a location 10 cm dorsocaudal to the tuber coxae at an angle of 45 degrees. The insertion site was standardized to a depth of 8 cm. Tissue homogenates were assayed f or TP and maximal activity of CS, HOAD, and LDH, All samples were run in du plicates and comparisons performed using a paired Student's t-test (signifi cance set at P < 0.05), Altitude did not change CS, HOAD or TP. CS for pre- altitude and altitude averaged 31.2 +/- 1.9 and 32.6 +/- 4.4 mu moles/g/min , respectively (P = 0,51). HOAD values averaged 17.9 +/- 2.1 and 18.2 +/- 2 .9 mu moles/g/min, respectively (P = 0.85). Altitude acclimatization decrea sed LDH activity. Pre-altitude and altitude LDH averaged 725.4 +/- 43.4 and 672.7 +/- 51.5 mu moles/g/min, respectively (P = 0.04). The decrease in LD H is consistent with decreases in skeletal muscle observed in other mammals at high altitude and suggests that muscles do not become more glycolyctic in altitude hypoxia.