Arai K, Ohno T, Saeki T, Mizuguchi S, Kamata K, Hayashi I, Saigenji K, Murata T, Narumiya S, Majima M
Department of Internal Medicine, Kitasato University School of Medicine, Sagamihara, Kanagawa 228-8555, Japan.
Gut. 2003 Sep;52(9):1242-9. doi: 10.1136/gut.52.9.1242.
We previously reported that endogenous prostaglandin I(2), generated by a mild irritant, sensitised calcitonin gene related peptide (CGRP) containing sensory nerves and facilitated the release of CGRP and gastric mucosal protection against ethanol. Administration of capsaicin also inhibited ethanol induced gastric mucosal injury through immediate release of CGRP from primary sensory neurones, which is termed the neural emergency system. In the present study, we tested whether endogenous prostaglandin I(2) also modulates the cytoprotective action of capsaicin using prostaglandin I receptor knockout mice (IP(-/-)).
The stomachs of IP(-/-) or their wild-type counterparts (IP(+/+)), anaesthetised with urethane (1.225 g/kg), were doubly cannulated from the oesophageal and duodenal sides, and the gastric mucosa was perfused (1 ml/min) with physiological saline. Perfusate was changed to 50% ethanol alone, or 50% ethanol containing capsaicin (16 approximately 1600 micro M). The injured area was estimated at the end of each perfusion experiment. In some animals, CGRP-(8-37), a CGRP antagonist (0.3 mg/kg), or indomethacin (1 mg/kg) was intravenously injected before perfusion of 50% ethanol containing capsaicin.
Capsaicin inhibited the injured area in a dose dependent manner. Fifty per cent ethanol containing capsaicin (480 micro M) immediately increased intragastric levels of CGRP although 50% ethanol alone did not. The protective action of capsaicin (480 micro M) against ethanol was completely abolished by intravenous injection of CGRP-(8-37). Indomethacin also inhibited the protective action of capsaicin, and this was accompanied by reduced levels of intragastric CGRP. Intragastric levels of prostaglandin E(2) were not increased by capsaicin treatment but those of 6-keto-prostaglandin F(1alpha), a metabolite of prostaglandin I(2), were markedly increased. No protective action of capsaicin was observed in IP(-/-) which lacked the ability to increase intragastric CGRP levels in response to ethanol containing capsaicin. The CGRP content of the stomach from untreated IP(-/-) did not differ from those in IP(+/+). Capsaicin (160 micro M) together with intragastric perfusion of beraprost sodium (PGI(2) analogue, 2.5 micro g/ml) showed enhanced protection against ethanol induced injury. This enhanced protection was completely blocked by intravenous injection of CGRP-(8-37).
The present results suggest that endogenous prostaglandin I(2) enhances the protective action of the capsaicin mediated neural emergency system against ethanol induced gastric mucosal injury through enhancement of CGRP release.
我们之前报道过，一种轻度刺激物产生的内源性前列腺素I(2)可使含降钙素基因相关肽（CGRP）的感觉神经致敏，并促进CGRP的释放以及胃黏膜对乙醇的保护作用。给予辣椒素也可通过初级感觉神经元立即释放CGRP来抑制乙醇诱导的胃黏膜损伤，这被称为神经应急系统。在本研究中，我们使用前列腺素I受体基因敲除小鼠（IP(-/-)）来测试内源性前列腺素I(2)是否也调节辣椒素的细胞保护作用。
用氨基甲酸乙酯（1.225 g/kg）麻醉的IP(-/-)小鼠或其野生型对照（IP(+/+)）小鼠，从食管和十二指肠侧进行双插管，并用生理盐水以1 ml/min的速度灌注胃黏膜。灌注液换成单独的50%乙醇，或含辣椒素（16～1600 μM）的50%乙醇。在每个灌注实验结束时估计损伤面积。在一些动物中，在灌注含辣椒素的50%乙醇前静脉注射CGRP拮抗剂CGRP-(8 - 37)（0.3 mg/kg）或吲哚美辛（1 mg/kg）。
辣椒素以剂量依赖性方式抑制损伤面积。含辣椒素（480 μM）的50%乙醇可立即增加胃内CGRP水平，而单独的50%乙醇则不能。静脉注射CGRP-(8 - 37)可完全消除辣椒素（480 μM）对乙醇的保护作用。吲哚美辛也抑制辣椒素的保护作用，同时胃内CGRP水平降低。辣椒素处理未增加胃内前列腺素E(2)水平，但前列腺素I(2)的代谢产物6 - 酮 - 前列腺素F(1α)水平显著升高。在缺乏对含辣椒素乙醇反应性增加胃内CGRP水平能力的IP(-/-)小鼠中未观察到辣椒素的保护作用。未处理的IP(-/-)小鼠胃内的CGRP含量与IP(+/+)小鼠无差异。辣椒素（160 μM）与胃内灌注贝拉前列腺素钠（PGI(2)类似物，2.5 μg/ml）一起显示出对乙醇诱导损伤的增强保护作用。静脉注射CGRP-(8 - 37)可完全阻断这种增强的保护作用。
目前的结果表明，内源性前列腺素I(2)通过增强CGRP释放来增强辣椒素介导的神经应急系统对乙醇诱导的胃黏膜损伤的保护作用。
