Effect of hypoxia and adenosine on the microvascular reserve in the rabbit heart

This study was done to determine if the unperfused reserves of arterioles and capillaries in the rabbit heart can be utilized independently. Anesthetized, open-chest rabbits were subjected to control, hypoxia or adenosine treatment. The animals were given 100 mg/kg FITC-dextran and the hearts were removed and sectioned for analysis of perfused and total arteriolar and capillary morphology. The fluorescence was used to photograph the perfused microvessels and the slides were then stained for visualization of all microvessels. Standard morphometric techniques were used to determine total and perfused morphometric indices for these microvessels. Mean arteriolar total density (Na) was 4.4 arterioles/mm2 for control, adenosine, and hypoxia groups with approximately half (52%) of control arterioles perfused. Most of the adenosine (92%) and hypoxia (82%) group arterioles were perfused. Mean capillary total Na was 2143 capillaries/mm2 for all groups with approximately half (60%) of control capillaries being perfused. Nearly all capillaries were perfused during hypoxia (96%) while the percent perfused capillarity with adenosine (80%) was between those numbers for control and hypoxia groups despite completely perfused arterioles. The arteriolar and capillary reserves can be utilized independently as adenosine treatment resulted in complete arteriolar perfusion while not resulting in complete capillary perfusion.