What is the required reperfusion period for assessment of myocardial infarct size using triphenyltetrazolium chloride staining in the rat?

Measurements of infarct size by use of tripenyltetrazoliumchloride (TTC) is a widely accepted method used to delineate the extent of myocardial necros is following coronary occlusion and reperfusion in various animal experimen ts. There is controversy, however, regarding the optimal reperfusion time f or estimating the maximally infarcted area by TTC staining in the rat. We t ested six different reperfusion times following 90 minutes of regional myoc ardial ischemia. Group 1 had 5 minutes of reperfusion (n = 6), group 2 had 30 minutes of reperfusion (n = 6), group 3 had 1 hour of reperfusion (n = 6 ), group 4 had 2 hours of reperfusion (n = 6), group 5 had 3 hours of reper fusion (n = 6), group 6 had 4.5 hours of reperfusion (n = 6). Risk areas, m easured by the use of blue dye, were similar among the 6 study groups. Infa rct size as a percent of risk area was 57 +/- 11% in group 1, 74 +/- 7% in group 2, 61 +/- 9% in group 3, 71 +/- 5% in group 4, 70 +/- 5% in group 5, and 64 +/- 9% in group 6 (x +/- standard error [SE]). There was no signifca nt difference in infarct size between the groups. However, prior to 60 minu tes of reperfusion, patches of pink and white areas were observed within th e risk regions, indicating a more difficult assessment of proper delineatio n of outer regions of necrotic tissue. For acute assessment of infarct size , reperfusion for 60 minutes or more is optimal because the infarct does ap pear homogeneous at that time and does not become larger with longer reperf usion periods.