Activation of ?-opioid receptor by U50,488H improves vascular dysfunction in streptozotocin-induced diabetic rats February 28, 2015 BMC Endocrine Disorders 2015, 15:7Â doi:10.1186/s12902-015-0004-7 Xuan Zhou and Dongjuan Wang contributed equally to this work. Published: 28 February 2015