Effect of diabetes and hypothyroidism on the predominance of cardiac myosin heavy chains synthesized in vivo or in a cell-free system.

Rat cardiac ventricular myosins and RNA were prepared from normal, diabetic, insulin-treated diabetic, hypothyroid, and 3,3',5-triiodo-L-thyronine-treated hypothyroid rats. Myosin heavy chains isolated from purified myosin or synthesized in vitro from cardiac RNAs were subjected to partial protease digestion during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was found that peptide maps obtained from cardiac myosin heavy chains of hypothyroid and diabetic rats were identical but differed from the maps of myosin heavy chain from control and hormone-treated animals. The same results were obtained, whether the heavy chains were isolated from purified myosin synthesized in the intact heart or from translation products coded for by cardiac RNAs added to the modified reticulocyte lysate. These results indicate that the myosin heavy chain RNA species present in the hypothyroid heart is also expressed during insulin deficiency but differs from the species expressed in normal animals. The expression of the two myosin heavy chain RNA species found in the rat cardiac ventricle appears to be independently regulated by these two hormones.