Muscle proteins and DNA in rat quadriceps during growth

Abstract

Before studying work hypertrophy utilizing deoxyribonucleic-acid (DNA) as a reference standard for intracellular changes, it is necessary to differentiate the effect of growth on DNA and structural proteins. In 22 rats of the same strain sacrificed between 43 and 155 days of life, total DNA of quadriceps rose to a fixed level in 90 days; sarcoplasmic and myofibrillar proteins, in 140 days. Growth was therefore associated with proliferation of nuclei along with hypertrophy of muscle in the first 90 days, and with hypertrophy along in the following 50 days. The implications of these findings are that biochemical study of muscle response to exercise at the present state of knowledge must be dissociated from the influence of growth itself, which induces changes similar in quantity and quality to exercise; that DNA after a definite age is a satisfactory reference standard, at least under ordinary laboratory conditions; and that age of "chemical maturity" of a cell varies according to the particular consituents.