Factors accounting for growth and atrophy of the heart.

Growth of the rat heart was induced by intrathoracic aortic banding, while atrophy followed hypophysectomy. During the early phase of hypertrophy, RNA concentration increased markedly. During the period of atrophy, RNA concentration was reduced. These changes in RNA concentration seemed to account for either the increased or the decreased rates of protein synthesis that was observed during hypertrophy or atrophy, respectively. Rates of protein degradation were unaffected during changes in heart size. These findings suggest that alterations in synthesis, processing, or degradation of RNA play a key role in modification of heart size.