Glucocorticoid modulation of cardiac mass and protein

We have examined glucocorticoid actions in the heart on the basis of their ability to 1) produce changes in ventricular mass, 2) influence total protein synthesis, and 3) alter myosin, a glucocorticoid-inducible protein. Cardiac hypertrophy of 6-20% has been demonstrated following treatment with various natural or synthetic steroids. The enlargement can occur rapidly within 2 d, yet recent evidence suggests that the increased mass is lost with prolonged treatment. Total protein synthesis rates have not been consistently observed to increase during the growth phase and are reduced to 50-60% of control rates by 7 d of hormone injections. Myosin heavy chain synthesis also is not elevated during the growth phase and is also reduced by 1 wk of treatment. Ventricular relative isomyosin content (V1, V2, V3), as determined by pyrophosphate gel electrophoresis, is shifted from V1 to V3 by approximately 10% after 11 d of steroid treatment. These results demonstrate that the glucocorticoid induction of increased ventricular mass is temporary under certain conditions. The down-regulation of the myosin heavy chains may prove as a potentially important protein for understanding the regulation of cardiac catabolism caused by glucocorticoids.