The Roles Of CNP-NPR-B-cGMP Signal Pathway In Renal Ischemia Reperfusion Injury

Ischemia reperfusion (IR) may caused renal structural and functional injury in kidney. Because of the renal particularity of structure and function, kidney was showed especially sensitive for ischemia reperfusion injury (IRI). Therefore, there were common renal diseases in clinical patients such as acute renal failure (ARF) and showed high morbidity and mortality in patients. Experimental data demonstrated that atrial natriuretic peptide (ANP)may reduced reperfusion injuries of the heart, liver, and the stomach etc and showed evident protective effcts in human and several animals. Is was also demonstrated that ANP may had protective function in IRI rat kidney via increase renal glomerular filtration rate, blood flow in medullar and reduce of epithelial cells injury in renal medullar and therefore recuperates integrality of dubular epithelial cells. On the other hand, ANP my reduces neutrophilic activity, inhibits secreiton of mediators of inflammations and reduces production of reactive oxygen species. However, the mechanism of ANP on ischemia reperfusion injury especially for ARF is not well kown.Natriuretic peptides (NPs), as a family of hormen, thare are four members in NPs I. E. ANP, brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). NPs may induce diuresis, sodium excretion, vessel dilatation, blood pressure regulation and electrolyte balance. The heart sythesis and release of ANP and BNP. CNP is sythesised by endothelial cells and play paracrine function in serise of tissues, such as the heart, vessel, nervous system etc. There are three types of the NP receptors (NPRs), NPR-A, NPR-B and NPR-C (NP clearance receptor). ANP and BNP mainly bingding to NPR-A and CNP maily bingding to NPR-B. Several experiments indicate that NPs and NPRs distributed in kidney but effects of NPs-cGMP on renal ischemia reperfusion injury are not clear. Therefor, the purpose of the precent is to investigate the effect of CNP-NPR-B-cGMP signaling pathway on renal ischemia reperfusion injury by using rat renal ischemia reperfusion model. immunohistochemistry methods, RT-PCR, ELISA etc. The renal structural changes are observed by microscope. Renal superoxide dismutase (SOD) activities, malondialdehyde (MDA) levels, Bax and Bcl-2 gene expressions are also to detected. In addition, creatinine (Cr) and blood urine nitrogen (BUN) levels are measured by autobiochemicaldetector. On the other hand, the rats will be randomly divided into three groups:sham operration group(sham), IR group(IR)and IR+CNP group (IR+CNP) (n=8 in each groups).The results of the precent experiments as follows:1. Levels of Cr and BUN were increaseed by time-dependent manna after renal ischemia reperfusion (n=8, P<0.01 vs sham goup).2. In sham group, renal organization was clearly and epithelial cells of tubules were completed, only a minor inflammatory cells were observed. In IR group, under microscope can be seen near the end of the epithelial cells from an empty bubble and particles of tunica adventitia. The flat, the paint off, or fate, the detachment of the epithelial cells, inflammatory exudate. The basement membrane is bare. Glomerular and kidney arterioles not change. sham group the structure of under electronic microscope is normal, mitochondria integrity, not swell, rough endoplasmic reticulum structural integrity; and IR group the nephridial tube epithelial cells microvilli off, mitochondria turgescence, mitochondria and endoplasmic abnormal reticulum distention, primary and secondary mixed up in a body and empty cell can also see that there is increasing. even the epithelial cells from collapse, and only thus is bare or break the substrate.3. The levels of CNP were unchanged in sham and IR groups (n=8, P>0.05 vs sham group).4. Expression of CNP mRNA were increased in IR group rats and showed time-dependent manna (n=8, P<0.05). The peake of CNP mRNA expression were observed at 2 houres after perfused in rats.5. In sham group, immunohistochemical data demonstrated that NPR-B were distributed widly in kidney. In IR group, renal NPR-B were increased compared with sham group significiently. RT-PCR data of NPR-B were similarly about with the immunohistochemical data.6. After RIR the histological morphologh analysis demonstrated phathologic change significantly. The electron microscope data indicated that IR caused mitochondrial injury and showed obviously swelling, some of the cristae became vacular-like; the microvilli of the Proximal tubule cells were scare and swelled, rough endoplasmic reticulums were reduced in number, foamy changes in the structure of nuclear and cytoplasm were also observed. In CNP group, the microvilli were slightly swelled or kept intact; the cristae of the mitochondria were slightly changed but the structure was still intact; rough endoplasmic reticulums were slightly swelled ribsome was all preserved, nuclear had almost normal figure with very clear nucleolus.7. Serum levels of Cr and BUN in IR group rats were significantly increased after reperfused for 24 hours (n=8, P<0.001vs sham group), and the serum levels of Cr and BUN were significantly reduced by CNP pretreatment after renal ischemia reperfusion (n=8, P<0.05 vs IR group).8. In IR group, the MDA contents were increased and SOD activity were significantly reduced after renal reperfusion (n=8, P<0.001and P<0.05 vs sham group). CNP may significantly reduced levels of MDA and slightly increased the activity of SOD after ischemia reperfusion in rat kidney (n=8, P<0.001and P<0.05 vs sham group).9. Reanal Bax gene expression was increased by ischemia reperfusion injury (n=8, P<0.05 vs sham or IR+CNP groups) without changes of Bcl-2 expression, but the ratio of Bax/Bcl-2 was decreased by CNP treatment in IR+CNP group (n=8, P<0.05 vs IR group).Thease results indicat that:1. Ischemia reperfusion my causes renal structural and functional injury especially in renal junctional zone of the cortex and medulla in rat kidney.2. Renal ischemia reperfusion injury induces up rangulation of CNP and NPR-B mRNA expression in rat kidney.3. CNP may improves renal structrue and function in ischemia reperfusion injury rat kidney.4. CNP has been shown antioxidant effect in rat kidney.5. CNP has been shown antiapoptosis effect in ischemia reperfusion rat kidney via up regulation of Bax/Bcl-2 ratio pathway.