REASONS FOR PERFORMING STUDY

The role of molecular signalling pathways in the phenotypic adaptation of skeletal muscle to different exercise stimuli in the Thoroughbred horse has not been reported previously.

OBJECTIVE

To examine CKM, COX4I1, COX4I2 and PDK4 gene expression following high intensity sprint and moderate intensity treadmill exercise stimuli in skeletal muscle of Thoroughbred horses.

MATERIALS AND METHODS

Two groups of trained 3-year-old Thoroughbred horses participated. Group A (n = 6 females, n = 3 males) participated in an incremental step test (moderate intensity) to fatigue or HR(max) on a Sato high speed treadmill (distance = 5418.67 m ± 343.21). Group B (n = 8 females) participated in routine 'work' (sprint) on an all-weather gallop (distance = 812.83 m ± 12.53). Biopsy samples were obtained from the gluteus medius pre-exercise (T(0)), immediately post exercise (T(1)) and 4 h post exercise (T(2)). For physiological relevance venous blood samples were collected to measure plasma lactate and creatine kinase concentrations. Changes in mRNA expression were determined by quantitative real-time RT-PCR for creatine kinase muscle (CKM), cytochrome c oxidase subunit IV isoform 1 (COX4I1), cytochrome c oxidase subunit IV isoform 2 (COX4I2) and pyruvate dehydrogenase kinase, isozyme 4 (PDK4) genes. Statistical significance (α < 0.05) was determined using Student's t tests.

RESULTS

COX4I2 mRNA expression decreased significantly in Group A and remained unchanged in Group B between T(0) vs. T(2) (-1.7-fold, P = 0.017; -1.0-fold, P = 0.859). PDK4 mRNA expression increased significantly in Group B but not in Group A between T(0) vs. T(1) (3.8-fold, P = 0.039; 1.4-fold, P = 0.591). There were no significant changes in the expression in CKM or COX4I1 mRNA abundance in either group.

CONCLUSIONS

Different exercise protocols elicit variable transcriptional responses in key exercise relevant genes in equine skeletal muscle due to variation in metabolic demand.