Eribis peptide 94 (EP 94) is a novel enkephalin analog, thought to interact with the and delta-opioid receptors. The purpose of the present study was to examine the cardioprotective potential of EP 94 in two clinically relevant porcine models of myocardial ischaemia and reperfusion, and to investigate if such an effect is associated with an increased expression of endothelial nitric oxide synthase (eNOS). Forty-one anesthetized pigs underwent 40 min of coronary occlusion followed by 4 h of reperfusion. In Protocol I, balloon occlusion of the left anterior descending artery was performed with concurrent intravenous administration of (A) vehicle (n = 7), (B) EP 94 (1 ug/kg) after 5, 12, 19 and 26 min of ischaemia (n = 4) or (C) EP 94 (1 ug/kg) after 26, 33, 40 min of ischaemia (n = 6). In Protocol II, open-chest pigs were administered (D) vehicle (n = 6) or (E) 0.2 ug/kg/min of EP 94 (n = 6) through an intracoronary infusion into the jeopardized myocardium, started after 30 min of ischaemia and maintained for 15 min. The hearts were stained and the protein content of eNOS measured. EP 94 reduces infarct size when administered both early and late during ischaemia compared with vehicle (infarct size group A 61.6 +/- 2%, group B 50.2 +/- 3% and group C 49.2 +/- 2%, respectively, P < 0.05), as well as when infused intracoronary (infarct size group D 82.2 +/- 3.9% and group E 61.2 +/- 2.5% respectively, P < 0.01). Phosphorylated eNOS Ser(I177) in relation to total eNOS was significantly increased in the group administered EP 94. indicating activation of nitric oxide production. (c) 2010 Elsevier B.V. All rights reserved.