Exercise induced changes in creatine kinase and aspartate aminotransferase activities in the horse: Effects of conditioning, exercise tests and acepromazine

Abstract

The study was designed to evaluate the change in creatine kinase (CK) and aspartate aminotransferase (AST) activity in normal horses following a conditioning program, exercise tests and the administration of acepromazine. Nine Thoroughbred horses, with no prior history of muscle disorders and no conditioning for 9 months, were assessed. During 11 weeks of conditioning CK and AST were assessed weekly and all horses had raw and mean CK and AST activities within normal limits. Although changes were noted in CK activity across time, these were not biologically significant. An initial exercise test over 400 meters prior to and then after conditioning, resulted in increased CK and AST activity immediately after and 4 hours after exercise. The increase in CK activity immediately after exercise was attributed to plasma volume changes and muscle leakage, while the increase in AST activity was attributed to plasma volume changes. The changes in CK and AST activity at 4h were attributed to muscle leakage. Conditioning did not affect the response of CK or AST activity to exercise. Increasing the distance and duration of maximal exercise from 400 to 1,000 meters caused increases in CK and AST activity at all sample times after exercise. The increase in CK and AST activity at 30 minutes and 4 hours were attributed to leakage from muscle or increased muscle membrane permeability. The administration of acepromazine IV prior to exercise over 1,000 meters failed to alter the response of CK and AST activity. Although statistically significant changes in CK and AST activity occurred following exercise, in no test were they biologically significant, being within normal limits.