Calcitonin Gene-related Peptide Improves The Function Of Mice Ischemia-reperfusion Heart Via NEP Way

Background:CGRP,a principal transmitters in capsaicin-sensitive sensory nervers,is widerly distributed in cardiovascular tissues,which possesses numerous physiological propertides.Previous studies have shown that CGRP can protect against myocardial injury induced by ischemia-reperfusion in the isolated perfused rat heart.However, the mechanism responsible for the protective effects of ischemic myocardium is still unclear. In addition to its direct protectic efforts on the ischemic myocardium by binding its receptors. This study aimed to investigate CGRP protect against myocardial injury whether through potentiates the effects of substance P by the competition of CGRP and substance P for the same catabolic enzyme,neutral endopeptidase(NEP).Objective:Observe exogenous CGRP exerts a cardioprotective effect against myocardial IR injury and investigate CGRP protect against myocardial injury whether through potentiates the effects of substance P by the competition of CGRP and substance P for the same catabolic enzyme,neutral endopeptidase(NEP).Methods:Experiments were conducted on the isolated reperfused mice heart. Hearts quickly hung on the Langendorff experimental apparatus and were perfused with Krebs-Henseleit solution(95%O2/5%CO2,37℃,at constant pressure of80mm Hg) in the presence of CGRP、CGRP8-37(a selective CGRP receptor antagonist,10-6mol/L)、 RP67580(a selective neurokinin-1[NK1] receptor antagonist,10-6mol/L) and Thiorphan(a neutral endopeptidase[NEP] inhibitor,10-/mol/L). All the isolated mice hearts were allowed to stabilize for25min prior to a period of40min global ischemia followed by30min of reperfusion. Left ventricular developed and diastolic pressures(LVDPand LVEDP),hearts rate(HR) were measured with medlab software and perfusate(coronary flow) was collected during the30min reperfusion.SP release were measured by radioimmunoassay during reperfusion.Results:Compared with IR group, pretreatment with CGRP (10-/mol/L) witnessed an obvious improvement of cardiac function, with a significant increase of LVDP, HR and CF but an obvious reduction in LVEDP. It suggested that CGRP can improve the heart function recovery of ischemia in mice. Blockade of the CGRP receptor with CGRP8-37(IR+CGRP+CGRP8-37group) caused a decline of LVDP, HR and CF but an increase of LVEDP. But the result is still better than that of IR group. The fact that CGRP8-37has not completely blocked the cardio protective effect of CGRP indicates that the CGRP receptors play a role in cardiac protection, but it is not only realized by their receptors, there are other ways. The study found that when SP receptor is blocked by NK1receptor (RP67580) antagonist, there is a significant decline of LVDP, CF and HR but a significant increase of LVEDP, when compared with the IR+CGRP group. In addition when exogenous CGRP is applied, the SP concentration in the perfusate of ischemic heart increased significantly,which indicates the cardiac protection of CGRP may realized by the degradation or release of SP. Pretreatment with thiorphan in the presence of CGRP (IR+CGRP+Thiorphan),the cardiac function has an improving trend by increasing CF and the concentration of substance P in the perfusate was significantly increased in this group when compared to CGRP group. The postischemic recovery of LVDP、LVEDP、HR and CF between IR+CGRP+CGRP8-37+Thiorphan group and IR+CGRP8-37+Thiorphan group tended to similar,indicating that the protective of CGRP in heart was completely blocked when CGRP receptors and NEP pathways were blocked by CGRPg-37and thiorphan respectively.Conclusions:(1)CGRP is play an important role in cardiac protection during ischemia-reperfusion in mice.(2)In addition to the CGRP receptor pathway,CGRP also affects the degradation and release of SP through NEP pathway to achieve the purpose of improving cardiac function...