The myocardial capillary vasculature in repeated physical exercise. An experimental investigation in the rat

The neoformation of myocardial blood capillaries was investigated on cardiac autoradiograms from 3H-thymidine injected rats that had been swimming-exercised for two weeks, rats that had been resting for three months following the exercise, and rats in which the rest had been followed by a second two-weeks period of exercise. The initial period of exercise induced a signficant capillary neoformation in the hearts. The newly-formed vasculature was found of functional significance still at the end of the resting period and available for the increased demands on the myocardial vasculature when the exercise was resumed.

The myocardial capillary vasculature in exercising animals with increased cardiac pressure load

The myocardial capillary reaction was studied in normal rats subjected to swimming exercise and in rats in which aortic stenosis had been produced at various time intervals before the swimming exercise was commenced. The data obtained indicated that neoformation of myocardial capillaries during swimming exercise occurred only in rats without aortic stenosis. It is concluded that a heart subjected to an increased pressure load is less able to respond to a superimposed volume load by an increase in its capillary supply than is a normal heart.