GTPCH並非出血性休克誘發之肝內一氧化氮合成速率的決定因子

GTPCH Is Not a Rate-limiting Factor for Hemorrhagic Shock-induced Hepatic Nitric Oxide Biosynthesis

背景：出血性休克會導致可誘導性一氧化氮(NO)合成酵素(iNOS)的表現增強，並且造成NO的製造增加。在此一創傷出血所促進NO生成增加的機制中，肝臟乃是其主要作用器官之一。Tetrahydrobiopterin(BH4)是iNOS活性的必須輔助因子，而Guanosine triphosphate cyclohydrolase I (GTPCH)是其合成速率的決定性酵素。現有的研究報告中，對於出血性休克之於肝臟GTPCH活性表現的影響所知甚少。方法：十五隻雄性Sprague-Dawley大白鼠隨機分配成三組：第一組為控制組(Sham)；第二組為持續出血性休克組(HS)；第三組為出血性休克合併急救組(HS/RES)。在HS及HS/RES組別中，實驗控制出血休克為維持平均動脈壓40-45毫米汞柱達60分鐘之久，爾後在HS/RES組使用自體輸血及等張生理食鹽水進行急救復甦。微透析探頭置於肝臟及右心房進行樣本採取；樣本所得之NO濃度由chemiluminescence進行分析。肝臟內iNOS及GTPCH mRNA濃度則由半定量之RT-PCR進行分析化驗。結果：出血性休克會引致肝臟的iNOS mRNA活化表現，進而造成肝臟及血中NO的合成增加。使用自體輸血及生理食鹽水進行急救，可以使此一激活現象正常化；然而各組別的肝臟GTPCH mRNA平均濃度並沒有顯著差異。結論：本研究結果顯示因出血性休克引發的NO合成，牽涉到肝臟組織內iNOS基因表現的活化；而GTPCH的表現則不受出血性休克或急救復甦的影響。再者，微透析分析不失為一連續樣本追蹤抽取技術的良好方法。

Background: Hemorrhagic shock upregulates inducible nitric oxide (NO) synthase (iNOS) expression and the resultant NO overproduction. Liver is one of the major organs that is responsible for increased NO production after trauma-hemorrhage and resuscitation. Guanosine triphosphate cyclohydrolase I (GTPCH) is the rate-limiting enzyme for the synthesis of tetrahydrobiopterin (BH4), a necessary co-factor for iNOS activity. Very little is known about the effects of hemorrhagic shock on hepatic GTPCH expression. Methods: Fifteen male Sprague-Dawley rats were randomly assigned to one of three groups, i.e. a sham instrumented (Sham) group, a sustained hemorrhagic shock (HS) group, and a hemorrhagic shock with resuscitation (HS/RES) group (n = 5 in each group). Controlled hemorrhagic shock was induced and the mean arterial pressure (MAP) was kept between 40-45 mmHg for sixty minutes in both HS and HS/RES groups. Then resuscitation with infusion of shed autologous blood and normal saline was performed in HS/RES group. Microdialysis probes were put in the liver and the right atrium for collection of serial samples. NO concentrations in dialysate samples were measured using chemiluminescence. Hepatic iNOS and GTPCH mRNA concentrations were analyzed using semiquantitative reverse transcription and polymerase chain reaction (RT-PCR). Results: Hemorrhagic shock induced both the hepatic and circulating NO biosynthesis as well as hepatic iNOS mRNA expression. Resuscitation with shed blood/normal saline normalized this upregulation. However, no difference was found in mean hepatic GTPCH mRNA concentrations between groups in this experiment. Conclusions: We provide the evidence that hemorrhagic shock-induced NO biosynthesis involves upregulation of iNOS transcription in liver tissue and GTPCH transcription is unaffected by either hemorrhagic shock or resuscitation. Furthermore, microdialysis is an ideal technique for serial sampling and that events can be followed.