CHANGES IN THE PLANTARIS MUSCLE AS AN INDICATOR OF ALTERATIONS IN LEAN BODY-MASS OF OBESE ZUCKER RATS FOLLOWING PROLONGED ENERGY RESTRICTION AND SUBSEQUENT PARTIAL RECOVERY

To study the effects of a prolonged (80 day), severe (64% body mass lo ss) energy restriction and subsequent refeeding on skeletal muscle tis sue, specifically the plantaris muscle, 21 genetically obese Zucker ra ts were selected for this study. Six rats were initially killed and se rved as baseline (BASE), then 15 rats underwent severe energy restrict ion for 80 days. Seven of these restricted rats (RESTRICT) were then k illed and assessed while the other eight rats (REHAB) were fed a dry r ehabilitation diet that provided 100% of the recommended energy and 1. 5 times the recommended protein for growth. Once the REHAB rats had re covered approximately 45% of their original mass loss, these animals w ere then evaluated. Within 20 min after being killed, the plantaris mu scles from each animal in each group had been removed, weighed, and fr ozen. Analyses included total plantaris mass, as well as differences i n fiber diameters, esterase activity, and fiber type distributions bet ween three groups (BASE, RESTRICT, and REHAB). The extreme body mass l oss of 64% in genetically obese Zucker rats resulted in significant ti ssue weight loss and reduced fiber diameters in the plantaris muscle. Refeeding resulted in larger muscle fiber diameters that approached ba seline values but an 11% difference in muscle weight remained and may be due to a decreased fiber number. Esterase activity seemed to indica te an initial fat utilization for the RESTRICT group, followed by supp ressed esterase activity in the REHAB group, suggesting increased fat storage. No significant differences Were found in fiber type distribut ion between BASE, RESTRICT, or REHAB animals.