Thyroidal and neural control of myosin transitions during development of rat fast and slow muscles

Experiments with developing euthyroid, hypothyroid and hyperthyroid rats show that the transition from neonatal to adult fast myosin is orchestrated by thyroid hormones acting directly upon fast muscle cells. Denervation studies reveal the switch from neonatal to adult fast myosin synthesis is independent of the motoneuron. However the synthesis of slow myosin during development is critically dependent on innervation.