Effect of acute coronary occlusion on the size of the dynamically perfused coronary capillary bed in the dog

The aim of the present study was to investigate the influence of reduced left anterior descending (LAD) coronary arterial blood flow on the size of the perfused coronary capillary surface area (CCSA) in dogs. The transcoronary hydrolysis (v) of the specific ACE substrate, [³H]benzoyl- Phe-Ala-Pro, was estimated and the parameter A(max)/K(m) (proportional to the size of the perfused CCSA) was calculated. By means of a ligature placed around the LAD, LAD blood flow was transiently reduced to 36.0 ± 4.1 (E₁) and 17.4 ± 4.3% (E₂) of control; in a separate maneuver the first diagonal branch of the LAD was ligated to achieve 40.0 ± 6.7% (E₃) of control flow. The v values remained unchanged at around 0.7 for E₁, E₂ and E₃ determinations, suggesting unaltered substrate transit time through the coronary capillary bed. A(max)/K(m) values decreased to 36 ± 5, 17 ± 4, and 47 ± 10% of control for E₁, E₂, and E₃ determinations, respectively, reflecting a flow-proportional decrease in CCSA. Values of the transpulmonary measures of v and A(max)/K(m) performed at the beginning and end of the protocol were unchanged. These results support the hypothesis that reduction in coronary blood flow will produce proportional decreases in the size of the CCSA. This new procedure can thus serve as a useful tool for investigating alterations in the size of the CCSA in different species and under various pathophysiologic challenges.