['Although matrix metalloproteinase (MMP) activity increases, endothelial function decreases after myocardial infarction (MI). The antibiotic doxycycline inhibits MMP activity in vitro. The role of doxycycline-mediated MMP inhibition in endothelial function is unclear.', 'Doxycycline ameliorates endothelial dysfunction, in part, by inhibiting MMP activity.', 'We subjected Sprague-Dawley male rats to MI by ligating the left anterior descending arteries. We subjected another group of rats to sham surgery. We administered doxycycline in drinking water (0.67 mg/ml) to both groups 2 days before surgery: the sham group underwent sham surgery and received doxycycline therapy, and the MI group underwent MI and received doxycycline therapy (n = 6 in each group). After 4 weeks, we anesthetized rats and prepared left ventricular rings from infarcted-ischemic (I), non-infarcted near-infarcted (NI), and sham surgery hearts with and without doxycycline treatment.', 'The MMP-2 activity increased significantly in I and NI hearts, and we observed a selective increase in MMP-9 activity only in I hearts, when compared with other groups (p < 0.05), measured by zymography. Cardiac inhibitor of metalloproteinase decreased only in I hearts (p < 0.05 vs other groups), measured by Western analysis, and doxycycline treatment reversed this decrease. Contractile response of rings to acetylcholine was attenuated in the I group, suggesting nitric oxide-mediated dysfunction, and was reversed by doxycycline. The response to nitroprusside was attenuated in I hearts and ameliorated by doxycycline, suggesting cardiomyocyte dysfunction. Bradykinin induced relaxation in rings from sham surgery hearts and from NI hearts, but induced paradoxic contraction in rings from I hearts. Treatment with doxycycline reversed the paradoxic contraction.'] Does doxycycline ameliorate ischemic and border-zone remodeling and endothelial dysfunction after myocardial infarction in rats?