Role Of Kappa Opioid Receptors In Vasculopathy Of Diabetic Rats And The Related Mechanisms

Diabetes mellitus (DM) is considered by the WHO as one of the major threats to human health in the 21st century. The major causes of morbidity and mortality in diabetic patients are cardiovascular complications involving both conduit arteries and microvessels. Furthermore, endothelial dysfunction, as determined by vasomotor dysfunction, is an early sign of diabetic vasculopathy and an independent predictor of cardiovascular risk.Endogenous opiod peptides (EOPs) contains three major subtypes, such as Enk, End, Dyn, with the correspondingμ,δandκopiod receptors. It has been confirmed that EOPs and opiod receptors are widespread in cardiovascular systems, and the heart is able to synthetize and release EOPs. As a result, we can draw the conclusion that EOPs and opiod receptors play an important role in the modulation of cardiovascular action.The alteration ofκopiod receptors (KOR), a predominant subtype of opioid receptors existing in vessels, may be one of the causes of cardiovascular diseases. Studies have proved that the failing human heart with ischemic and other etiology has a distinct reduction in KOR expression, and a reduced capacity for the opioid-dependent regulation and cardioprotection. Activation of KOR was proved to be beneficial to lots of cardiovascular diseases, such as hypertension, ischemic heart disease and pulmonary hypertension, and so on. However, it is unclear about its effects on diabetic vasculopathy. So in the present study, we investigated whether KOR activation directly protects diabetic vessels and how it works. The results of the present investigation provide rationale and support for a novel class of the kappa opioid modulators in the prevention and treatment of diabetic vasculopathy.Objectives:1. To determine whether the expression of KOR is changed in arteries of DM rats.2. To determine whether U50,488H, the selective KOR agonist, or nor-BNI, the selective KOR antagonist, has effects on the expression of KOR in arteries of DM rats.3. To investigate the effects of KOR activation or inhibition on the mesenteric arterial vasomotoricity of DM rats.4. To investigate the effects of KOR activation or inhibition on the aortic structure of DM rats.5. To determine whether KOR activation or inhibition has effects on the related vasoactive factors of DM rats.6. To determine whether KOR activation or inhibition has effects on the related inflammatory factors of DM rats.Methods:1. The model of DM rats was set by single intravenous injection of STZ (50 mg/kg).2. The densities of KOR protein in the aortas of rats were measured by immunohistochemical staining.3. The densities of KOR protein in the mesenteric arteries of rats were determined with Western blot techniques.4. The vasomotoricity was evaluated with mesenteric arterial rings.5. The changes of the aortic structure were detected with HE stain and transmission electron microscope.6. The level of serum AngⅡand the level of serum sICAM-1 were detected by ELISA kits.7. The changes of protein expression of eNOS and NF-κB in the mesenteric arteries of rats were determined with Western blot techniques.Results:1. KOR distributed primarily in the tunica intima layer of the aortas.2. The expression of KOR increased in both the aortas and the mesenteric arteries of the DM rats, and administration intraperitoneally of U50,488H (1.0 mg/kg/day for 10 days), a selective KOR agonist, further up-regulated the expression of KOR in the rats while administration intraperitoneally of nor-BNI (0.5 mg/kg/day for 10 days), a selective KOR antagonist, down-regulated the expression of KOR in the DM rats.3. In the DM rats, the vasomotoricity of mesenteric arterial rings was significantly abnormal compared with the control rats (p < 0.05); the protein expression of eNOS decreased and the protein expression of NF-κB increased (p < 0.01); both the level of serum AngⅡand the level of serum sICAM-1 were raised (p < 0.01); the aortic structure showed signs of disorder obviously.4. U50,488H treatment on the DM rats alleviated the disorder of mesenteric arterial vasomotoricity (p < 0.05) and aortic structure; increased the protein expression of eNOS and decreased the protein expression of NF-κB (p < 0.01); down-regulated both the level of serum AngⅡand the level of serum sICAM-1 (p < 0.01).5. Nor-BNI treatment on the DM rats aggravated the disorder of mesenteric arterial vasomotoricity (p < 0.05) and aortic structure; decreased the protein expression of eNOS and increased the protein expression of NF-κB (p < 0.01); up-regulated both the level of serum AngⅡand the level of serum sICAM-1 (p < 0.01).Conclusions:1. KOR distributed primarily in the tunica intima layer of the aortas.2. The expression of KOR increased in both the aortas and the mesenteric arteries of the DM rats, which could be further up-regulated by the selective KOR agonist, U50,488H, or be down-regulated by the selective KOR antagonist, nor-BNI.3. Activating KOR may alleviate the abnormality of mesenteric arterial vasomotoricity and aortic structure in diabetic rats by improving endothelial function and decreasing chronic inflammation while inhibiting KOR may work oppositely. The results of the present investigation provide rationale and support for a novel class of the kappa opioid modulators in the prevention and treatment of diabetic vasculopathy.