Effect of combination of stresses on myocardial metabolism.

The effect of hypoxia, exercise, and thermal stress on myocardial metabolism have been widely investigated, but little attention has been paid to studying the effects of a combination of these stress. The influence of hypoxia as modified by physical exertion (swimming) and cold stress was therefore studied. The parameters investigated included myocardial glycogen and noradrenaline, serum free fatty acid, adrenal ascorbic acid, and adrenal weight. It was observed that maximal stress was produced when hypoxia was combined with physical exertion. No suppression of cold-induced lipolysis by hypoxia was observed, in contrast to previously reported observations. Maximal depletion of cardiac blycogen and cardiac noradrenaline was noted in hypoxic exercise. Adrenal overactivity was not found to be related to any particular stress but was seen to be proportional to the severity of the stress applied.