The Effects Of Intrathecal Injecting Fentanyl To Visceral Pain Of Acute Inflammatory Rats On The Expression Of NA_v1.8 In DRG

Objective:To observe the effects of intrathecal injecting fentanyl to visceral pain of acute inflammatory rats on the expression of Nav1.8 in dorsal horn and to explore the mechanisms in the analgesic effect of fentanyl on the treatment of acute inflammatory visceral pain, and to guide the clinical use of fentanyl as an analgesic to treat patients with visceral pain.Methods:32 male 250-300g SD rats were randomly divided into 4 groups (n=8): groupⅠnormal control (group NS); groupⅡto groupⅣwere exposed to saline, fentanyl, naloxone respectively (group AS, F, NF). Rats were weighed and anesthesia by injected 3.5% chloral hydrate intraperitoneally 10ml/kg, blunt dissection rat L3, L4 space, and the catheters were intrathecaled. Determine the rats 3 days after surgery, all rats with non-limb dysfunction were intrathecal injected 2% lidocaine 20μl. Those rats'lower limbs paralysis occurs immediately and restore movement in 5 min would included in the experiment. The model of an acute inflammatory visceral pain was made by injection of peritoneal cavity. Observed and recorded behavior of each group's response 1h to calculated the visceral pain scores by Schmauss standard. After, all rats were anesthetized by 3.5% chloral hydrate 10ml/kg injected intraperitoneally, perfused with normal saline 4℃, completed removal of rat thoracic spinal DRG for the Nav1.8 RT-PCR and Western-blot test.The influence of fentanyl on the spinal DRG Nav1.8 in rats which suffer visceral pain caused by acute inflammation, was detected by behavioral score, expressions of Nav1.8 mRNA and Nav1.8 protein.Results:Compared with the control group ( group NS) , the writhing test scores of group AS, F and NF were increased significantly( P<0.05). The writhing test scores of group F and NF were decreased significantly compared with group NS( P<0.05). Compared with the control group ( group NS) , the expression of Nav1.8 mRNA and protein of three groups rats which suffered from inflammatory pain (group NS, F and NF) was increased significantly( P<0.05). Protein and mRNA of Nav1.8 were downregulated in group F and group NF while Protein and mRNA of Nav1.8 were upregulated in group AS.Conclusions:Intrathecal injection of fentanyl to spinal DRG by inhibiting the expression of Nav1.8 channels in acute inflammatory pain in rats with visceral analgesic effect.