The effect of regular physical exercise on sensitivity to ischaemia in the rat's heart.

The effect of different training regimes (three programmes of both swimming and running exercise) on the heart hypertrophy index and some biochemical indices was evaluated and compared individually with the sensitivity of the corresponding heart to ischaemia in order to elucidate the significance of training intensity and observed changes in the development of heart ischaemic injury. The sensitivity of the heart to ischaemia, evaluated by the rate of development of ischaemic contracture 48 h after completing the exercise programme, increased in parallel with an increase in the heart hypertrophy index. Experiments with different swimming programmes showed that the extent of cardiac hypertrophy increased together with an increase in the duration of everyday swimming bouts. Hypertrophied hearts from trained rats were characterized by greater mobilization of glycogen and increased incorporation of 32P into ATP when investigated 10 min after isoprenaline administration. During total ischaemia the development of ischaemic contracture was accelerated in catecholamine-stimulated trained hearts due to more rapid hydrolysis of ATP compared with that in the hearts from sedentary animals. It is suggested that the observed difference between hearts from sedentary and trained animals is, at least partially, connected with the higher sensitivity of myofibrils to Ca2+ in trained hearts.