Early adaptations to training: Upregulation of alpha-myosin heavy chain gene expression

Purpose: To determine whether changes in left ventricular (LV) contractile elements are an early adaptation to chronic exercise. Methods: Rats were randomly assigned to sedentary control or exercise training groups for 1 or 10 wk of training. After training, the LV was analyzed for protein by Western blot or mRNA by Northern and real-time QRT-PCR analysis. Results: Plantaris cytochrome oxidase activity was significantly (P < 0.05) increased by 1 wk (+28%) or 10 wk (+32%) of training. Training significantly increased LV myofibrillar alpha-MHC protein and alpha-MHC-mRNA after both training periods. No changes in myofibrillar beta-MHC protein or beta-MHC-mRNA were observed. After 1 wk of training, LV skeletal a-actin-mRNA was significantly increased, whereas no changes were found for ANF, glyceraldehyde dehydrogenase, or cytochrome oxidase IV. Gel mobility shift analysis determined that YY1 DNA binding was significantly decreased in LV extracts from trained animals, although no change in YY1-mRNA expression was observed. Conclusions: Increased myofibrillar alpha-MHC protein and alpha-MHC-mRNA expression are early events in the adaptation to chronic exercise and occur before significant cardiac growth. These adaptations enhance myocardial contractility and permit increases in maximal cardiac output during heavy exercise.