Study On Opioid's Regulation Of Gene Expression Of The Key Enzyme Glutamate Dehydrogenase In Amino Acid Catabolism

Opium has long been applied for pain relief. However addictive property of opioid alkaloid made heroin and morphine abuse a worldwide problem of medical science and society. Heroin has a higher addictive potential than morphine. Mechanisms about addiction , endurance and withdraw of opioid have been studied comparatively deep-going, while study on opioid's effect on peripheric tissue is scare. The purpose of our study is to reveal effect of heroin on amino acid catabolism through researching heroin's modulation on gene expression of glutamate dehydrogenase (GLDH) which is the key enzyme in amino acid catabolism .In this study, 50 adult male Wistar rats were averagely divided into 5 groups at random. The groups were handled respectively as follows:Gruop1 i.p. N.S. for 9 days and were killed on 10th day;Group2 i.p. heroin for 3 days and were killed on 4th day;Group3 i.p. heroin for 9 days and were killed on 10th day;Group4 i.p. heroin for 9 days and were killed on 13th day;Group5 i.p. heroin for 9 days and were killed on 18th day.Rats' plasma and tissues were collected right after execution and were stored in －20℃ refrigerator and liquid nitrogen separately for later use .GLDH activity in plasma,parietal lobe, liver and small intestine were determined . Total RNA in parietal lobe,liver and small intestine were extracted respectively for RT-PCR and Southern blot so that content of GLDH mRNA in these tissues could be estimated.Parietal lobe GLDH gene expression is restrained by heroin. Both RT-PCR and Southern blot results of GLDH mRNA content in heroin dependent and withdrawal groups turn out to be lower than control group (p<0.01) at the same time. So, heroin adjusts GLDH gene expression at transcription level, and we can not exclude the existence of modulation at translation and post-translation level yet. Heroin's effect on parietal lobe GLDH gene expression results in reduced GLDH activity which may be followed by insufficient amino acid oxidization and then energy supplying to the brain and excessive glutamate in the brain which play a important role in withdrawal symptoms. GLDH abounds in liver. Result of RT-PCR for liver shows that 3 days heroin dependent group has a lower GLDH mRNA than control group do while 9 days dependent group has the same GLDH mRNA level as 3 days heroin dependent group. GLDH mRNA in 3 days withdrawal groups is higher than control group and become equal to control group after 8 days withdraw. Result of Southern blot identical to that of RT-PCR assures us the reliability of both outcomes. So, heroin can restrain GLDH gene expression in liver at transcription level. Liver GLDH activity in both two heroin dependent groups is lower than control group. 3 days withdrawal group is higher than control group and 8 days withdrawal group decline to control group level. It means that heroin decreases GLDH activity in liver. GLDH activity increases in 3 days withdrawal group may result from a rebound after a sudden withdraw. GLDH mRNA's alteration in quantity is identical to that of GLDH activity infer that heroin adjust GLDH gene expression in liver at transcriptional level and we can't exclude translation and post-translation modulation yet. Small intestine is one of the most important targets of opioid. Opioid decreases mobility of the stomach and intestine, resulting in constipation, loss of appetite and so on. Long-term of opioid administration leads to reduced food intake and loss of weight due to chronic suppression of appetite, malnutrition, reduced resistance to infections and even cachexia. When usage of opioid is stopped, excessive mobility of the bowel leads to diarrhea which can also contribute to weight loss. Does amino acid metabolism of the organism take part in the loss of weight? Our research gives you the answer as follows. GLDH mRNA content of 3 days and 9 days heroin dependent group are higher than that of control group and are 1.50-fold and 3.01-fold of the control group respectively. Withdrawal groups show a declinati...