High-dose morphine has been extensively used in the control of postoperative and cancer pain. Patients receiving prolonged administration of high-dose morphine are known to be associated with certain cardiovascular complications and tissue regeneration defects. This research thesis aims to investigate the biological effects and molecular mechanisms of high-dose morphine on the vascular endothelial function, angiogenesis and wound regeneration using murine models of morphine-dependence and cultured endothelial cell assays. Mice were subjected to placebo or morphine (20 mg/kg, i.p.) injection for consecutive 14 days. Aortas were harvested for assessment of vasomotor function by isometric force recordings. Protein expression p47phox (a major subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase) was determined by Western blotting. Generation of superoxide anions was detected under confocal microscope. Endothelium-dependent relaxations to acetylcholine were significantly reduced in morphine-treated animals, but were normalized by superoxide scavenging. Fluorescent densities of dihydroethidium and expression of p47phox were increased in the aorta of morphine-treated mice. In the second part of this thesis, the candidate determined the effects of high-dose morphine on angiogenesis and mobilization of endothelial progenitor cells (EPCs) in a mouse model of excisional wound injury. Excisional wound was created on control and morphine-dependent mice. Wound healing was compared by measuring the final-to-initial wound area ratio. Generation of superoxide anions in the wound was determined by luminol-enhanced chemiluminescence. Circulating mononuclear cells were isolated and measured for EPC (defined as CD34+/CD133+ cell) counts. In vivo and in vitro measurements of angiogenesis following morphine treatment were performed using the Matrigel assay. The results showed that wound closure was significantly reduced in mice treated with morphine when compared with controls, and higher levels of superoxide anions were generated in these wounds. High-dose morphine reduced numbers of circulating EPCs following creation of excisional wound. Matrigel assay showed impaired angiogenesis in animals and reduced capillary tube formation in cultured endothelial cells treated with high-concentration of morphine. Collectively, this research thesis demonstrated a number of novel findings. First, high-dose of morphine impairs vascular endothelial function by increased production of vascular superoxide anions. Activation of NADPH oxidase may be the molecular mechanisms responsible for reduced bioavailability of endothelium-derived NO. Second, systemic administration of high-dose morphine delays healing of excisional wounds and impairs angiogenesis. This antiangiogenic effect is associated with increased superoxide anions production and impaired mobilization of EPCs. In line with direct endothelial dysfunction, impaired angiogenesis and EPC mobilization resulted from high-dose morphine treatment may cause increased cardiovascular morbidity in human subjects receiving higher therapeutic dose of morphine.