Long-term protection of ischaemic myocardium by nitroglycerin ointment

To assess whether the reduction in ischaemic injury during acute myocardial infarction induced by nitroglycerin (NTG) results in a decrease in tissue necrosis, 96 rats were assigned to two groups. The first group (n=34) was sham-operated. The second group of 62 rats was randomised in a ratio of 2:1 into control (n=43) and treated (n=19) subgroups following coronary artery occlusion. Treated animals received an application of 2% NTG ointment every 8 h immediately post-occlusion. All rats were killed 48 h after coronary artery occlusion and total creatine kinase activity (CK) of the left ventricle (LV) was measured. Infarct size calculated by CK depletion was 65.2±14.3% (mean±SD) of LV in control rats, and 51.6±14.0% of LV in NTG-treated (p<0.02). In a further series of 46 rats with coronary occlusion, the area of infarcted myocardium 21 days post-occlusion was assessed by planimetry on histological sections. In rats with control occlusion (n=22), the extent of infarction was 30.6±4.8% of LV, and in NTG-treated rats (n=24) it was 16.2±5.8% of LV (p<0.001). The amount of scar tissue in the infarcted myocardium 21 days post-occlusion was also determined by measuring LV hydroxyproline and collagen content in an additional 32 rats randomly assigned to a control (n=11), a NTG-treated (n=9) and a sham-operated group (n=12). By this method, infarct size 21 days post-coronary occlusion was 37.4±2.6% of LV in control animals and 22.3±2.6% of LV in NTG-treated animals (p<0.001). In conclusion, this study shows that NTG given as 2% ointment to rats with coronary occlusion may protect myocardium from ischaemic necrosis, and that this effect is sustained, resulting in the formation of smaller scars.