Effects of Emphysema on Skeletal Muscle Fiber Atrophy in Hamsters

Abstract

2289 Patients afflicted with this emphysema demonstrate altered peripheral skeletal muscle fiber composition and fiber atrophy. It is unknown whether these alterations occur in muscles composed of a given fiber type or oxidative capacity. PURPOSE: Therefore, the purpose of this investigation was to determine whether emphysema induces fiber transformation or atrophy in respiratory and locomotory muscles with diverse fiber types and metabolic profiles. METHODS: Fiber composition and cross-sectional area (CSA) were measured in selected hindlimb muscles and diaphragm of male Syrian golden hamsters 6 months following intratracheal instillation of either saline (CON=7) or elastase (EMP=15). Activity levels were restricted in both groups by individually housing animals in small cages. RESULTS: Excised lung volume increased 145% with emphysema (CON=1.2 ± 0.2 g; EMP=2.8 ± 0.5). Fiber composition was largely unaltered, with the exception of a 13% reduction in IIB fibers in tibialis anterior muscle of emphysema animals. Type I fiber size was also mainly unaltered, except for a diminished (19%) CSA in plantaris muscle. However, fiber CSA of fast-twitch types IIA, IIX and/or IIB fibers were reduced in caudal biceps femoris (IIA=34%, IIX=26%, and IIB=29%), vastus lateralis (IIX=27% and IIB=23%), tibialis anterior (IIX=46% and IIB=46%), gastrocnemius (IIX=23%), and plantaris (IIA=32% and IIX=24%) muscles of hamsters with emphysema. In contrast, there was a trend for emphysema to increase the CSA of type IIA fibers in diaphragm. CONCLUSION: These data demonstrate that emphysema induced atrophy primarily affects muscles composed of fast-twitch fibers with varying degrees of oxidative capacity (citrate synthase activity: caudal biceps femoris=20μmol/min/g; plantaris = 52). Supported by ALA RG-013-N and NIH HL-50306.