EXERCISE OF HEAT-EXPOSED RATS PREVENTS MYOCARDIAL PATHOLOGY

1. Light and electron microscope morphometry has been used to study th e effect on heart morphology of a sedentary life style in normothermic (24-degrees-C) and warm acclimated (34-degrees-C) rats in comparison with exercised normothermic and warm acclimated rats. 2. The sedentary acclimated rats had multiple foci of myocardial necrosis while the ex ercised rats did not. The capillary to myofibre ratio and the number o f mast cells were higher in the acclimated exercised hearts than in he arts from all the other groups. The intercapillary distance and the mi tochondrial volume fractions were not affected by any treatment regime . 3. It is concluded that although some neoangiogenesis occurs during exercise + heat, the neoangiogenesis does not explain the absence of m yocardial pathology produced by heat alone.