[Effect of thyroxine and 2,4-dinitrophenol on cardiac energetics]

The administrations of 1-thyrohine (20 mg/kg) for two sucessive daysin the rats or 10(-3) M 2,4-dinitrophenol (2,4-DNP) in vitro reduced the mechanical of the heart in working isolated preparations of the rat heart. Oxygen consumption of inactive heart did not react to thyroxine and significantly increased after 2,4-DNP administration. The reduction of the heart efficiency due to thyroxine is, probably, associated with a decreased efficiency of mechanochemical conjugation in the myocardium muscular fibers.