Delayed Preconditioning Induced By Monophosphoryl Lipid A In Rat Intestine

Monophosphoryl lipid A (MLA) is a detoxified derivative of endo-toxin and was first derived and purified from bacterial lipoplysaccharide in 1980s. MLA is one of the most well documented protective drugs against cardiac ischemic/reperfusion injury in various animal species, most of them focus on cardiac delayed preconditioning Mechanisms involved with the MLA-induced cardioprotection are still not fully understood. Recently, He et al reported that MLA induced delayed preconditioning is mediated by calcitonin gene-related peptide (CGRP) in rat hearts. We haven't got the same study about MLA in the peripheral vascular bed (the anse intestinalis of rat). So the present study examined whether MLA could mimicked the delayed preconditioning in rat intestine and whether endogenous CGRP is involved in this process.In this study, we first investigated the protective effects in the anesthetized rat small intestine of MLA (ip, 500 g-kg-1) in vivo experiment. The ischemic/reperfusion (I/R) injury was made by 30 min of ischemic and 1 hour reperfusion. The MLA group was injected with MLA (500 g'kg-1 ), intraperitoneally (ip) 24 hour before the experiment. From the result we can see: the group of I/R myeloperxidase (MPO), creatinekinase (CK), dehydsogenase (LDH), molondialdehyde (MDA) respective-ly is (10.18 0.50) U-g-1, (106.83 8.44) U-ml-1, (1014.82 141.19) U-L-1, (2.69 + 0.52) nmol-mg-1 (protein wt), the group of MLA respectively is (7.64 0.41) U-g-1, (66.03 7.51) U-ml-1, (472.17 36.71) U-L-1, (1.34 0.45) nmol-mg-1 (protein wt), P<0.05. The latter compared with the former have significantly difference. We assayed the CGRP content in the plasma after ischemic /reperfusion.We found MLA could promote the release of CGRP: the group of I/R was (43.54 2.70) pg-ml-1, (85.48 3.98) pg-ml-1 was the group of MLA, P<0.01. The result shows MLA could induced the delayed preconditioning in rat small intestine. Moreover, the protective effect is positive relative with the content of CGRP in plasma. This result revealed CGRP may play a role in the delayed preconditioning induced by MLA in rat small intestine.The second step we adopted the model of in situ perfusion in rat small intestine. The 1/R injury was made by 1 hour of ischemia and 15 min of reperfusion, the group of MLA was injected with MLA (ip, 500 g kg-1) 24 hour before the experiment. We observed whether MLA could mimicked the delayed preconditioning and whether CGRP is invloved in. The result showed that MLA could remarkably improve the tissue lesion. The group of I/R, LDH, MDA, CK respectively is (871.71 187.12) U-L -1, (4.28 1.35) nmol-mg-1 (protein wt), (17.31 4.04) U-ml-1; The group of MLA, LDH, MDA, CK respectively is (512.49 136.15) U-L-1, (2.22 1.19) nmol-mg-1 (protein wt), (11.14 2.04) U-ml-1. P<0.05. The further result revealed that CGRP was invloved in this process. We assayed the CGRP content in the effluence before and after ischemic /reperfusion. We found MLA could promote the release of CGRP: (45.34 11.77) pg-ml-1before I/R, (341.20 103.22) pg-ml-1 after I/R, P<0.01. The effect of preconditioning of MLA could abolished by CGRP8-37, a selective CGRP receptor antagonist. Pretreatment with capsaicin which specifically exhausted the transmitter content of sensory nerves, also abolished the protection of MLA. All these results suggest CGRP involves in the MLA-induced delayed preconditioning in rat small intestine.