Intercapillary distance and capillary reserve in hypertrophied rat hearts beating in situ.

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Abstract
Functional intercapillary distance (ICD) was measured in stop-motion photomicrographs of hypertrophied, normally compensated, well oxygenated rat hearts beating in situ. Left ventricular hypertrophy was produced by salt loading and unilateral nephrectomy. Minimum ICD (when all capillaries are open) also was measured. Ventricular weight increased by 30-40% within 8-9 weeks after nephrectomy. To compare the effect of normal and pathological growth, ICD was also measured in normal rats. In normal animals, minimum ICD and functional ICD increased linearly and proportionately with left ventricular weight. Consequently, the extent to which capillary recruitment could decrease ICD was the same in large and small normal hearts (about 2 micrometer). In the hypertrophied hearts, capillary recruitment could have maintained ICD within normal limits at rest for several weeks. After 8-9 weeks, however, the capillary reserve in hypertrophy was fully utilized at rest, and mean functional ICD was 1.5-2.0 micrometer greater than normal for the age of the animal. An analysis of O2 transport indicates that anoxic foci would exist throughout the hypertrophied heart and particularly in subendocardium when the capillary reserve is exhausted. The calculated amount of anoxic tissue appears sufficient to account for the focal necrosis and fibrosis observed in hypertrophy and for the development of circulatory failure.