Effects of Activity upon Tissues of the Rat

Abstract

This investigation was undertaken in order to determine the effect of different degrees of activity upon the weight and composition of tissues of growing animals. It was thought that this information might throw some light upon the mode of adjustment of the organism to the effects of chronic exercise and aid in the interpretation of observations made upon animals in which muscular activity was a variable factor. In this report are included observations of body and heart weights and the concentration of creatine, hemoglobin, total nitrogen and water in the skeletal muscle of 2 groups of albino rats. Litter mates after being weaned at the age of 5 weeks were equally distributed between 2 groups. The activity of one group, designated as inactive, was restricted by confining the animals to small individual cages for a period of 6 1/2 months. The cages measured 21 cm in diameter by 22.5 cm in height and were almost completely filled with cut paper to further restrict movement. The other group, referred to as active, were housed in revolving activity cages. 1 Food and water were allowed ad libitum. The animals were killed by bleeding from the cut liver. During the hemorrhage an infusion of saline solution was made into a femoral vein according to the technic described by Whipple, 2 in order to wash the tissues free from blood. The muscles of the unoperated limb were freed as far as possible from fat and connective tissue, clipped into fine bits and aliquots were taken for analysis. Muscle hemoglobin was estimated according to the method of Whipple. 2 The acid hematin standard was employed. Creatine was determined according to Rose, Helmer and Chanutin. 3 The excised heart was opened, compressed against blotting paper, weighed and then dried in an electric oven to constant weight.