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Opioids produce delayed pre-conditioning (PC) in vivo and in vitro. Our previous research revealed that opioid‑induced delayed PC has an antiapoptotic effect on pulmonary artery endothelial cells (PAECs) suffering from anoxia/reoxygenation (A/R) injury. The present study hypothesized that activation of endothelial mitochondrial ATP‑sensitive potassium (KATP) channels may result in antiapoptotic effects and against dysfunction in PAECs. Cultured porcine PAECs underwent 16 h anoxia treatment, followed by 1 h reoxygenation, which occurred 24 h following pretreatment with saline (0.9% NaCl; w/v) or morphine (1 µM). To determine the underlying mechanism, a selective mitochondrial KATP inhibitor, 5‑hydroxydecanoic acid (5‑HD; 100 µM), and an opioid receptor antagonist, naloxone (Nal; 10 µM), were administered 30 min prior to the A/R load. The percentage of apoptotic cells was assessed by Annexin V‑fluorescein isothiocyanate staining, using a fluorescence‑activated cell sorter. The mRNA expression of intercellular cell adhesion molecule‑1 (ICAM‑1) was measured by reverse transcription‑quantitative polymerase chain reaction. The endothelin‑1 (ET‑1) content in the supernatant of PAECs cultures was estimated by radioimmunoassay. Compared with the control, A/R caused the apoptosis of PAECs, release of ET‑1 and increased mRNA expression of ICAM‑1. Morphine‑induced delayed PC significantly reduced PAEC apoptosis, increased the release of ET‑1 and reduced the mRNA expression of ICAM‑1 by ~1.7‑times, compared with A/R. The protective effect of morphine was abolished by pretreatment with 5‑HD and Nal, however, the two agents themselves failed to aggravate the A/R injury. These results suggested that morphine-induced delayed PC has a protective effect during A/R injury of PAECs. This effect may be mediated by mitochondrial KATP channels and is opioid receptor-dependent.