Geometry of capillary networks in hypertrophied rat heart

Capillary geometry was examined in normal and hypertrophic myocardium. Hypertrophy was induced by aortic constriction in neonatal rats. Morphometric data were obtained from tissue sections exposed to a staining technique that distinguished the arteriolar and venular portions of capillaries by color. In sham-operated controls, the theoretical tissue region supplied by a single capillary decreased from the arteriolar to venular side (499 +/- 3 microns 2 and 456 +/- 5 microns 2, P less than 0.05; mean +/- SE) of capillaries. In hypertrophy, only arteriolar capillary tissue regions increased in size, thus enlarging the difference between arteriolar and venular ends (547 +/- 6 microns 2 and 464 +/- 5 microns 2, P less than 0.01). Intercapillary distances, measured at various levels along the capillary path length, decreased in a stepwise manner in both normal and hypertrophic hearts. In hypertrophic hearts, mean capillary path length was significantly longer than in controls, but the total length of the individual capillary nets was reduced. In both groups, arteriolar capillary segment length was longer (P less than 0.01) than venular capillary segment length. Given that PO2 values are lower on the venular side of capillaries, this spatially distinctive geometry in normal myocardium: smaller domains, shorter intercapillary distances and segment lengths, would provide favorable geometric conditions for oxygen diffusion. In hypertrophy, average intercapillary distance increased, and the distinction between arteriolar and venular portions of capillaries was further exacerbated.