Effects Of Aging, Compensatory Hypertrophy And Creatine Supplementation On Plantaris Cross-sectional Area And Nuclear Domain

Abstract

Compensatory hypertrophy increases the cross-sectional area (CSA) of muscle fibers. Creatine supplementation (CR) may increase muscle fiber size when combined with training and acts primarily on fast muscle fibers. CR combined with training may aid aging muscle against atrophy, particularly in fast muscle fibers. The nuclear domain (cytoplasm to myonucleus ratio) remains relatively constant through hypertrophy and atrophy, but may not be maintained with aging. PURPOSE Investigate CSA and nuclear domain in fiber types (I, IIA, IIB/D) of young and old rat plantaris muscles in response to compensatory hypertrophy and CR. METHODS Bilateral surgical ablation of the distal gastrocnemius muscle to induce compensatory hypertrophy of the plantaris muscle was performed on two groups of young (4mo) and old (23mo) rats. Another two groups of each age did not undergo surgery. Creatine monohydrate (4.45g/L in 5% dextrose, ad lib) was given to surgery and non-surgery groups. The groups not receiving CR (with or without surgery) received 5% dextrose. Following four weeks of supplementation the plantaris muscle was removed and assayed for fiber types (mATPase) and immunostained (dystrophin and laminin) for CSA and myonuclei and satellite cell counts. Age and group comparisons were made with 2-way ANOVA. RESULTS Muscles subjected to surgery, and surgery combined with CR (SCR), have larger CSA than control in type I and IIA fibers. This was demonstrated in young and old. SCR caused enlarged type IIB/D fibers in young but no difference was found in old. Comparing young and old animals (for each group), a larger CSA was found in type IIB/D of young muscles subject to CR and SCR, compared with old muscles. There was no difference between old and young for each group in type I or IIA fibers. Nuclear domain size did not differ with age, but surgery and SCR caused larger domain sizes in young type I fibers. Domains were larger in fast (IIA, IIB/D) fibers of young rats undergoing CR or SCR. CONCLUSIONS Together CR and compensatory hypertrophy surgery cause hypertrophy of all muscle fibers in young plantaris muscle. Type IIB/D fibers of old muscle do not hypertrophy, even after surgery and SCR. Nuclear domain is larger in young compared with old muscle subjected to CR and SCR.