Local and Systemic Responses to Repeated Gluteal Muscle Biopsies in Mature Sedentary Horses

Abstract

Repeated muscle collections are used to determine physiological responses to interventions, but little is known about the impacts of collections themselves. Twenty-six horses (8 geldings, 18 mares; mean±SD 9.5±3.5y) were used to test the hypothesis that repeated muscle collections would not impact mitochondrial function, antioxidant status, or markers of inflammation and muscle damage. Horses were assigned to have gluteus medius samples collected at: 0 and 24h (n=7); 0 and 6h (n=6); 0, 6, and 12h (n=7); or 0, 6, 12, and 24h (n=6). Blood was collected from all horses every 6h for 72h, starting 24h prior to initial muscle collection. Mitochondrial oxidative phosphorylation and electron transfer (E) capacities were determined via high-resolution respirometry, and mitochondrial volume density and function by citrate synthase (CS) and cytochrome c oxidase activities. Muscle was evaluated for malondialdehyde concentrations and activities of superoxide dismutase and glutathione peroxidase. Muscle and plasma concentrations of interleukin (IL)-4, IL-8, IL-10, and tumor necrosis factor-a were quantified, along with serum amyloid A (SAA) and cortisol concentrations and creatine kinase (CK) activity. Data were analyzed using linear models in SAS with time as a repeated measure, horse as the subject, time as a fixed effect, and sex. For blood parameters, additional fixed effects included group and time×group interaction. Integrative (per mg tissue) E supported by complex II decreased from 0 to 6h (P=0.004) but returned to 0h by 12h. Intrinsic (per unit CS) Leak was greater at 6 than at 0 and 12h (P<0.03) but did not differ from 24h. Activity of CS was greater at 0 than 12 and 24h (P≤0.02). Serum CK activity was similar from -24 through 0h but increased in all horses at 6h and remained elevated through 48h (P<0.05). Geldings had greater serum CK activity and plasma IL-8 concentrations than mares (P≤0.006). Serum cortisol concentrations displayed a circadian pattern throughout the collection period (P<0.0001). No other variable was impacted. In unstressed, mature horses, repeated gluteal collections did not profoundly impact physiological markers; however, CK should be interpreted cautiously during repeated tissue collections.