[Heart energetics and adaptation of the organism to temperature]

In working isolated preparations of the rat heart, effects of prolonged adaptation of the organism to cold (1-3 degrees) or warmth (25-27 degrees) as well as 10-minus 6 M noradrenaline administration on the efficiency (E) of the heart mechanical work, were studied. In the cold adaptation E decreases, i.e. the amount of warmth released by the heart through the same amount of work, increases. In the warmth adaptation the heart E increases. The respective changes of the heart warmth production are only revealed in the working heart, as the temperature adaptation has no effect on the O2 consumption by the stopped heart. Contrary to the skeletal muscles, the heart E during the cold adaptation does not decrease under effect of noradrenaline. In the control and, particularly, during the warmth adaptation, the heart E decreases under effect of noradrenaline.