Relationship of the Changes in Biogenic Amines to Nitric Oxide and Oxygen Free Radicals During Cerebral Ischemia/Reperfusion

Recently oxygen free radicals and nitric oxide (NO) are known to play an important role in neuronal reperfusion injury. This study was aimed to investigate the role of oxygen f ree radicals and NO during cerebral ischemia/reperfusion, using dimethylthiourea (DMTU) and NG-monomethyl-L-arginine (NMMA), an oxygen f ree radical scavenger and a competitive NOS inhibitor respectively. In the in vivo experiment, the ischemia/reperfusion-induced changes of cerebral biogenic amines were examined in Mongolian gerbil (Meriones unguiculatus) pre-treated with NMMA and/or DMTU. To induce cerebral ischemia/reperfusion, bilateral common carotid arteries were clamped for 10 minutes and then released for 15 minutes. The biogenic amines were measured by using HPLC-ECD(High Performance Liquid Chromatography-Electrochemical detection). To confirm the results from the in vivo experiments, the effect of NMMA and/or DMTU on [3H]dopamine release from striatal slices exposed to hypoxia was investigated. The results are as follows; 1) Ischemia/reperfusion increased the ratio of DOPAC/dopamine and HVA/dopamine as well as the concentrations of DOPAC and HVA, which were evident only in corpus striatum. 2) NMMA attenuated the ischemia/reperfusion-induced increase in the ratio of DOPAC/dopamine in corpus striatum. However, the change of DOPAC or HVA was minimal. 3) DMTU attenuated the ischemia/reperfusion-induced increase of DOPAC and HVA, and the ratio ofDOPAC / dopa- mine and HVA/dopamine in corpus striatum. 4) Simultaneous pre-treatment with NMMA and DMTU attenuated the ischemia/reperfusion-induced increase of DOPAC and HVA, and the ratio Of DOPAC/dopamine and HVA/dopamine in corpus striatum. The extent of attenuation was greater than the single treatment group with NMMA or DMTU. 5) Exposure to hypoxia markedly increased the release of [3H]dopamine in the striatal slices. 6) The administration of either NMMA or DMTU attenuated the increase of [3H]dopamine release induced by hypoxia in the striatal slices. 7) The administration of both NMMA or DMTU markedly attenuated the increase of [3H]dopamine release induced by hypoxia to the extent of the control in the striatal slices. These results suggest that oxygen free radicals play an important role in cerebral ischemia/reperfusion injury, for which NO seems to be responsible.

A Study of Endothelium-dependent Pulmonary Arterial Relaxation and the Role of Nitric oxide on Acute Hypoxic Pulmonary Vasoconstriction in Rats / 결핵

BACKGROUND: Since the demonstration of the fact that vascular relaxation by acetylcholine(Ach) results from the release of relaxing factor from the endothelium, the identity and physiology of this endothelium-derived relaxing factor(EDRF) has been the target for many researches. EDRF has been identified as nitric oxide(NO). With the recent evidences that EDRF is an important mediator of vascular tone, there have been increasing interests in defining the role of the EDRF as a potential mediator of hypoxic pulmonary vasoconstriction. But the role of EDRF in modulating the pulmonary circulation is not compeletely clarified. To investigate the endotbelium-dependent pulmonary vasodilation and the role of EDRF during hypoxic pulmonary vasoconstriction, we studied the effects of N(G)-monornethyl-L-arginine(L-NMMA) and L-arginine on the precontracted pulmonary arterial rings of the rat in normoxia and hypoxia. METHODS: The pulmonary arteries of male Sprague Dawley(300~350g) were dissected free of surrounding tissue, and cut into rings. Rings were mounted over fine rigid wires, in organ chambers filled with 20ml of Krebs solution bubbled with 95 percent oxygen and 5 percent carbon dioxide and maintained at 37℃. Changes in isometric tension were recorded with a force transducer(FT. 03 Grass, Quincy, USA). RESULTS: 1) Precontraction of rat pulmonry artery with intact endothelium by phenylephrine(PE, 10(-6)M) was relaxed completely by acetylcholine(Ach, 10(-9) -10(-5)M) and sodium nitroprusside (SN, 10(-9) -10(-5)M), but relaxing response by Ach in rat pulmonary artery with denuded endothelium was significantly decreased. 2) L-NMMA(10-4M) pretreatment inhibited Ach(10(-9) -10(-5)M)-induced relaxation, but L-NMMA(10-4M) had no effect on relaxation induced by SN(10(-9) -10(-5)M). 3) Pretreatment of the L-arginine(10(-4)M) significantly reversed the inhibition of the Ach(10(-9) -10(-5)M)-induced relaxation caused by L-NMMA(10(-4)M). 4) Pulmonary arterial contraction by PE(10(-6)M) was stronger in hypoxia than normoxia but relaxing response by Ach(10(-9) -10(-5)M) was decreased. 5) With pretreatment of L-arginine(10(-4)M), pulmonary arterial relaxation by Ach(10(-9) -10(-5)M) in hypoxia was reversed to the level of relaxation in normoxia. CONCLUSION: It is concluded that rat pulmonary arterial relaxation by Ach is dependent on the intact endothelium and is largely mediated by NO. Acute hypoxic pulmonary vasoconstriction is related to the suppression on NO formation in the vascular endothelium.