Opioid growth factor modulates angiogenesis

Objective: Induced angiogenesis has recently been attempted as a therapeuti c modality in patients with occlusive arterial atherosclerotic disease. We investigated the possible role of endogenous opioids in the modulation of a ngiogenesis. Methods: Chide chorioallantoic membrane was used as an in vivo model to stu dy angiogenesis. Fertilized chick eggs were incubated for 3 days, explanted , and incubated for an additional 2 days. Three-millimeter methylcellulose disks were placed on the surface of the chorioallantoic membrane; each disk contained opioid growth factor ([Met(5)]-enkephalin; 5 mu g), the short-ac ting opioid receptor antagonist naloxone (5 mu g), opioid growth factor and naloxone together (5 mu g of each), the long-acting opioid antagonist nalt rexone (5 mu g), or distilled water (control). A second series of experimen ts was performed with distilled water, the angiogenic inhibitor retinoic ac id (1 mu g), and vascular endothelial growth factor (1 mu g) to further eva luate our model. The developing vasculature was imaged 2 days later with a digital camera and exported to a computer for image analysis. Total number of blood vessels, total vessel length, and mean vessel length were measured within a 100-mm(2) region surrounding each applied disk. Immunocytochemica l analysis was performed with antibodies directed against opioid growth fac tor and its receptor (OGFr). Results: Opioid growth factor had a significant inhibitory effect on angiog enesis, both the number of blood vessels and the total vessel length being decreased (by 35% and 20%, respectively) in comparison with control levels (P < .005). The simultaneous addition of naloxone and opioid growth factor had no effect on blood vessel growth, nor did naloxone alone. Chorioallanto ic membranes exposed to naltrexone displayed increases of 51% and 24% in bl ood vessel number and length, respectively, in comparison with control spec imens (P < .005). These results indicate that the opioid growth factor effe cts are receptor mediated and tonically active. Immunocytochemistry demonst rated the presence of both opioid growth factor and OGFr within the endothe lial cells and mesenchymal cells of the developing chorioallantoic membrane vessel wall. Retinoic acid significantly reduced the number and the total length of blood vessels, whereas vascular endothelial growth factor increas ed both the number and the length of blood vessels in comparison with the c ontrols (P < .0001). The magnitude of opioid growth factor's effects were c omparable to those seen with retinoic acid, whereas inhibition of opioid gr owth factor with naltrexone induced an increase in total vessel length comp arable to that for vascular endothelial growth factor. Conclusions: These results demonstrate for the first time that endogenous o pioids modulate in vivo angiogenesis. Opioid growth factor is a tonically a ctive peptide that has a receptor-mediated action in regulating angiogenesi s in developing endothelial and mesenchymal vascular cells. (J Vasc Surg 20 00;32:364-73.).