Age-related changes in metabolic properties of equine skeletal muscle associated with muscle plasticity

The purpose of the present study was to determine the age-related changes in myosin heavy chain (MHC) composition and muscle oxidative and glycolytic capacity in 18 horses ranging in age from two to 30 years. Muscle samples were collected by excisional biopsy of the semimebranosus muscle. MHC expression and the key enzymatic activities were measured. There was no significant correlation between horse age and the proportions of type-IIA and type-IIX MHC isoforms. The percentage of type-I MHC isoforms decreased with advancing age. Muscle citrate synthase activity decreased, whereas lactate dehydrogenase activity increased with increasing age. Muscle 3-OH acyl CoA dehydrogenase activity did not change with ageing. The results suggest that, similar to humans, the oxidative capacity of equine skeletal muscle decreases with age. The age-related changes in muscle metabolic properties appear to be consistent with an age-related transition in MHC isoforms of equine skeletal muscle that shifts toward more glycolytic isoforms with age.     

Comparison of the Recurrence Rate of Gastric Dilatation with or Without Volvulus in Dogs after Circumcostal Gastropexy Versus Gastrocolopexy

OBJECTIVE: To compare the recurrence rate of acute gastric dilatation with or without volvulus (GDV) after circumcostal gastropexy (CCGP) or gastrocolopexy (GCP) in dogs. STUDY DESIGN: A prospective, double-blind, multicenter, randomized, controlled, clinical trial with two groups (A and B). ANIMALS: Fifty-four client-owned dogs presented for treatment of GDV. METHODS: Dogs with acute GDV that had not previously had a gastropexy performed were included. The preoperative treatment before gastropexy was standardized. A CCGP was performed on dogs in group A, and a GCP was performed on dogs in group B. Postoperative treatment was standardized, but deviation did occur according to the special needs of particular patients. A minimal follow-up time of 180 days was required for dogs not excluded from the study. The median follow-up time in group A was 700 days; in group B, it was 400 days. The occurrence of abdominal pain and gastrointestinal problems after surgery were recorded by the owners. RESULTS: There was no significant difference in the recurrence rate of GDV between the two groups. At the end of the study, the recurrence rate was 9% and 20% in group A and in group B, respectively. CONCLUSIONS: Both surgical techniques are effective in preventing recurrence of GDV.     

Ingestion of starch-rich meals after exercise increases glucose kinetics but fails to enhance muscle glycogen replenishment in horses

Fatiguing exercise substantially decreases muscle glycogen concentration in horses, impairing athletic performance in subsequent exercise bouts. Our objective was to determine the effect of ingestion of starch-rich meals after exercise on whole body glucose kinetics and muscle glycogen replenishment. In a randomized, cross-over study seven horses with exercise-induced muscle glycogen depletion were either not fed for 8 h, fed half of the daily energy requirements ( approximately 15 Mcal DE) as hay, or fed an isocaloric amount of corn 15 min and 4 h after exercise. Starch-rich meals fed after exercise, when compared to feed withholding, resulted in mild to moderate hyperglycemia (5.7+/-0.3 vs. 4.7+/-0.3 mM, P<0.01) and hyperinsulinemia (79.9+/-9.3 vs. 39.0+/-1.9 pM, P<0.001), 3-fold greater whole body glucose kinetics (15.5+/-1.4 vs. 5.3+/-0.4 micromol kg(-1)min(-1), P<0.05), but these only minimally enhanced muscle glycogen replenishment (171+/-19 vs. 170+/-56 and 260+/-45 vs. 294+/-29 mmol/kg dry weight immediately and 24 h after exercise, P>0.05). It is concluded that after substantial exercise-induced muscle glycogen depletion, feeding status only minimally affects net muscle glycogen concentrations after exercise, despite marked differences in soluble carbohydrate ingestion and availability of glucose to skeletal muscle.     

Effects of feeding meals with various soluble-carbohydrate content on muscle glycogen synthesis after exercise in horses

OBJECTIVES: To determine effects of feeding diets with various soluble-carbohydrate (CHO) content on rates of muscle glycogen synthesis after exercise in horses. ANIMALS: 7 fit horses. PROCEDURES: In a 3-way crossover study, horses received each of 3 isocaloric diets (a high soluble CHO [HC] diet, a low soluble CHO [LC] diet, or a mixed soluble CHO [MC] diet). For each diet, horses were subjected to glycogen-depleting exercise, followed by feeding of the HC, LC, or MC diet at 8-hour intervals for 72 hours. RESULTS: Feeding the HC diet resulted in a significantly higher glycemic response for 72 hours and significantly greater muscle glycogen concentration at 48 and 72 hours after exercise, compared with results after feeding the MC and LC diets. Muscle glycogen concentrations similar to baseline concentrations were detected in samples obtained 72 hours after exercise in horses when fed the HC diet. Rate of glycogen synthesis was significantly higher when horses were fed the HC diet, compared with values when horses were fed the MC and LC diets. Glycogen synthase activity was inversely related to glycogen content. Protein content of glucose transporter-4 was the lowest at 72 hours after exercise when horses were fed the HC diet. CONCLUSIONS AND CLINICAL RELEVANCE: Muscle glycogen synthesis was slower after glycogen-depleting exercise in horses, compared with synthesis in humans. Feeding HC meals after strenuous exercise hastened replenishment of muscle glycogen content, compared with results for feeding of LC and MC diets, by increasing availability of blood glucose to skeletal muscles.     

Effects of exercise and glucose administration on content of insulin-sensitive glucose transporter in equine skeletal muscle

OBJECTIVES: To characterize insulin-sensitive glucose-transporter (GLUT-4) protein in equine tissues and determine effects of exercise and glucose administration on content of GLUT-4 protein in equine skeletal muscle. SAMPLE POPULATION: Tissue samples from 9 horses. PROCEDURES: Western blot analyses were performed on crude membrane preparations of equine tissues to characterize GLUT-4. In a crossover, randomized study, horses were strenuously exercised for 3 consecutive days and then administered 13.5% glucose or isotonic saline (0.9% NaCl; control) solution, i.v., at similar infusion rates for 12.1 hours. Samples were collected from the middle gluteal muscle before and after exercise and 10.1 hours after completion of an infusion and used for measurements of glycogen concentration and total content of GLUT-4 protein. RESULTS: Immunoblot analyses detected specifically immunoreactive bands for GLUT-4 in insulin-sensitive tissues. Content of GLUT-4 protein in skeletal muscle increased significantly by 27.3 and 12.3% 22.2 hours after exercise for control and glucose groups, respectively. Intravenous infusion of glucose resulted in a significantly higher rate of glycogenesis, compared with results for the control group (mean +/- SD, 3.98 +/- 0.61 and 1.47 +/- 0.20 mmol/kg/h, respectively). Despite enhanced glycogenesis, we did not detect an increase in content of GLUT-4 protein after glucose infusion, compared with values after exercise. CONCLUSIONS AND CLINICAL RELEVANCE: GLUT-4 protein was expressed in equine skeletal and cardiac muscles. Exercise increased total content of GLUT-4 protein in skeletal muscle, and replenishment of muscle glycogen stores after glucose infusion attenuated the exercise-induced increase in the content of GLUT-4 protein in equine skeletal muscle.