| ObjectiveAbdominal pain is one of the most important symptoms in chronic pancreatitis, which is present in 80%-90% patients during the course of the disease. Alliviation of abdominal pain plays an important role in the treatment of chronic pancreatitis. The frequency, severity and other characteristics of pain in chronic pancreatitis have made the management of this disease difficult and unsatisfactory. Several hypotheses exist as to the basis for pain in chronic pancreatitis; however, the exact mechanisms have not been fully elucidated. Recently, the review about chronic pancreatitis pain has also showed that, according to data such as clinical features of the pain, biochemical and histological findings, spinal changes, and changes in the brain-gut axis, neuropathic pain is likely to play an important role during the course of chronic pancreatitis. In other words, this study demonstrates that drugs, which can effectively cure naturopathic pain such as gabapentin, can probably be used to treat pain in chronic pancretitis as well. Gabapentin (GBP) is a novel antiepileptic agent that has a well-established role in the treatment of chronic pain. It is particularly effective for neuropathic pain, such as diabetic neuropathy, postherpetic neuralgia and so on. In general, people consider that gabapentin binds theα2δ-1 subunits of voltage dependent calcium ion channels and blocks the development of hyperalgesia and central sensitization. Gabapentin reportedly enhance the analgesic effects of subtherapeutic dose morphine in a rat model of acute pancreatitis. Moreover, several studies have showed that gabapentin can be used as an ancillary drug to cure pain in chronic pancreatitis. However, no animal experiment so far shows any obvious evidence which can prove the treatment effects and the potential mechanisms of gabapentin. In this study, we aimed to develop a simple chronic pancreatitis model that would allow us to investigate the analgesic effects of gabapentin and the possible underlying cellular mechanisms.MethodsBehavioral tests:Chronic pancreatitis was produced by injection of dibutyltin dichloride (DBTC) dissolved first in 100% ethanol (two parts) and then mixed with glycerol (three parts). DBTC (8mg/kg body wt) was injected into the tail vein in a volume of 200μl solvent. Animals in the Sham group only received the solvent with the same volume. In the time course study, the belly areas of rats were tested by von Frey filaments (VFF) of various calibers before and once weekly for up to 4 weeks after induction of pancreatitis. During day 1 to day 6 of the last week, rats were tested 1 h after drug administration, and examined the effects of gabapentin 100mg/Kg i.p. on mechanical hyperalgesia.Morphology:At the end of the last behavioral study, the rats were killed and the pancreas was removed and fixed in 10% formalin in phosphate buffered saline (PBS) containing 1.0 mM MgC12 at 4℃overnight. Sections from paraffin-embedded specimens were stained with H&E to observe the pathological changes. In addition, liver and kidneys were harvested and processed at the same time to confirm the presence or absence of inflammation in these organs.Molecularbiological study:With the method of Real-time PCR and western blot, we investigated the expression ofα2δ-1 calcium channel subunit in spinal cord and effect of gabapentin treatment on the subunit expression. ResultsBehavioral tests:Compared to Sham group, Mean response frequencies of DBTC treated rats were significantly increase at every time point tested up to 4 weeks (P< 0.05).There was no significant change difference in responding to the stimuli between the DBTC-GBP group and the DBTC-SL group in Day 1 and Day 2. However, from Day 3 to Day 6, mean response frequencies of the DBTC-GBP group produced a significantly decrease compared to the DBTC-SL group (P<0.05), suggesting that the repeated injection of gabapentin could relieve mechano-hyperalgesia induced by DBTC induced.Pancreatic histology: 27 days after the induction of chronic pancreatitis, we observed the appearance of segmental gland atrophy, chronic inflammatory infiltrates, periductular and intralobular fibrosis, and large regions of acinar loss. By contrast, we observed no obvious morphological changes in pancreases of the Sham rats. In addition, there were no signs of inflammation in the liver and kidneys.Molecularbiological study:(1) The thoracic spinal cord (T8-11), which contain a high percentage of soma of pancreatic afferent nerves, was excised at 27 days after the induction of chronic pancreatitis. We found an statistically significant increase inα2δ-1 calcium channel subunit mRNA and protein levels indicated by Real-time PCR and western blot (P<0.01). (2) The thoracic spinal cord (T8-11) was dissected at Day 1 and Day 6 after repeated intraperitoneal injection gabapentin once a day in the last week. In Day 6, theα2δ-1 calcium channel subunit mRNA levels and protein levels in DBTC-GBP rats were statistically significantly downregulate compared to DBTC-SL rats (P<0.05).ConclusionIn the present study, we showed that repeated dosing of gabapentin by intraperitoneal injection could reduce mechanical hypersensitivity on the upper abdomen and produce analgesic effect in a rat model of chronic pancreatitis. Although the specific mechanisms for this antinociceptive effect are unknown, we believed that down-regulation ofα2δ-1 calcium channel subunit would be one of the mechanisms of action of this agent.
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