Geometry of capillary networks in volume overloaded rat heart

Volume overload cardiac hypertrophy was induced in male Sprague-Dawley rats by experimental aortocaval fistula. This procedure resulted in considerable increases in left ventricular mass (70%) by 21-23 days. Our objective was to study the effect of volume overload on the geometry of coronary capillaries in the left ventricular midmyocardium. Tissue sections were stained according to a protocol that distinguished arteriolar (AC) and venular (VC) capillary regions by color. Morphometric data were then collected and compared between AC and VC regions. In sham-operated controls (CON; n = 8), the tissue area (capillary domain) supplied by a single capillary decreased from AC to VC regions (AC = 505 +/- 5 microns 2: VC = 452 +/- 7 microns 2; P less than 0.01; mean +/- SE). In volume overloaded hearts (VOL; n = 8), only VC domain areas were reduced from control values (P less than 0.01) and the differences between AC and VC regions were preserved (AC = 480 +/- 5 microns 2; VC = 395 +/- 6 microns 2; P less than 0.01). Minimal capillary length was significantly longer in volume overloaded hearts (VOL = 723 +/- 18; CON = 581 +/- 20 microns; P less than 0.01). In the control group, AC segment length was longer than VC segment length (AC = 93 +/- 2 microns: VC = 74 +/- 2 microns; P less than 0.01). In volume overload, AC segment length was also longer than VC segment length, but the divergence between AC and VC regions was increased (AC = 108 +/- 3 microns; VC = 71 +/- 2 microns; P less than 0.01). These changes in capillary geometry may be secondary to specific changes in the arrangement and dimension of myocytes in the left ventricular wall following volume overload hypertrophy.