THE APPLICABILITY OF COLOR-LABELED MICROSPHERES IN A RABBIT MODEL OF ISCHEMIA-REPERFUSION

This study was designed to examine the ability of color-labeled micros pheres to depict different states of myocardial perfusion in a rabbit model of ischemia-reperfusion. A thread was passed under the left ante rior descending artery (LAD) and the first left marginal artery of ane sthetized New Zealand White rabbits. Blue-labeled microspheres (500/g body wt) were injected into the left atrium. The thread was tightened in rabbits belonging to the experimental group (n = 8), and red-labele d microspheres (500/g body wt) were injected. The snare was loosened, and yellow-labeled microspheres (500/g body wt) were injected before ( n = 5) or after (n = 3) methylene blue injection. In animals belonging to the ''sham'' group (n = 4 and n = 2, respectively), the sequence o f injections was similar, but the snare was not tightened. The animals were euthanized, and 0.3-1 g sections were cut from ischemic and noni schemic regions, as determined by methylene blue in the experimental s ubgroups and from the corresponding regions in the ''sham'' subgroups. The tissue samples were digested with 4 M KOH, ethanol 70%, and ultra sonication, and the microspheres were recovered by vacuum filtration. The dye was chemically removed from the microspheres, and the photomet ric absorption of each sample was determined. There was no significant difference between the experimental and ''sham'' groups in baseline u ptake of blue-labeled microspheres. Rabbits belonging to the experimen tal subgroups had significantly lower mean uptake of red microspheres during ischemia relative to ''sham'' (0.51 +/- 0.08 vs 1.06 +/- 0.24 a nd 0.36 +/- 0.19 vs 0.91 +/- 0.12, respectively). After loosening of t he snare there was no difference in uptake of yellow-labeled microsphe res. Color-labeled microspheres depict myocardial ischemia in the rabb it. The ability of color-labeled microspheres to depict reperfusion hy peremia remains to be proved.