Coronary capillaries during normal and pathological growth.

The adaptive capacity of the myocardium with respect to its capillary concentration and distribution has been measured morphometrically during the hypertrophic growth occurring physologically after birth and as a result of induced overload in the adult. In particular, the growth of the capillary network of the left ventricle was examined in rats from one to 150 days of age and in rats with spontaneous hypertension, aortic stenosis, two-kidney one-clip renal hypertension and myocardial infarction. The following quantitative structural parameters of the capillary microvasculature were analyzed: 1. Capillary luminal volume density; 2. Capillary luminal surface density; 3. The average diffusion distance for oxygen; and 4. The aggregate capillary length in the whole ventricle. The major conclusions of the present study are: 1. The postnatal growth of the heart is characterized by lengthening of the whole capillary network that is linearly related to the aging process; 2. The rate of capillary proliferation, measured by changes in capillary density, is greater in the first month of age; 3. In contrast to postnatal development, lengthening of the capillary microvasculature is not a consistent adaptive mechanism of induced cardiac hypertrophy; 4. Capillary luminal volume and surface densities and the diffusion distance for oxygen are essentially maintained in spontaneous, mechanical and renal hypertension; and 5. Cardiac hypertrophy in acute and healed myocardial infarction results in alterations of the capillary properties implicated in tissue oxygenation that may constitute the morphological counterpart of the greater vulnerability to ischemic episodes of the hypertrophied myocardium after infarction.