THE TRYPSINOGEN ACTIVATOR ENTEROKINASE PROMOTES PANCREATIC INFLAMMATORY PAIN

Abstract

Introduction: Premature activation of trypsin within the pancreatic acinar cells is an early event in acute pancreatitis which results in pancreatic parenchymal auto-digestion. Intrapancreatic injection of exogenous trypsin produces pain by potentiating capsaicin-induced activation of TRPV1, an ion channel specialized to integrate noxious inflammatory stimuli. Expression of fos protein in laminae I and II of the dorsal horn of the spinal cord is a validated measure of pancreatic nociception in the rat. Although the possibility that pancreatic trypsin promotes pain has been suggested by studies using exogenous trypsin, the significance of this finding depends upon the ability of endogenous trypsin to promote TRPV1activation and nociception. We hypothesized that injection of enterokinase into the pancreas would promote inflammation and activate pancreatic pain pathways via a mechanism involving TRPV1. Methods: Enterokinase (250μl, 100 U/ml over 10 min) or vehicle was injected into pancreatic duct of anesthetized rats prior to injection of the TRPV1 agonist capsaicin (250μl, 0.5 mg/ml over 10 min). Later pancreatic, serum, and spinal cord samples are obtained at 150 minutes. After 2.5 h tissue samples were removed and the following indices were measured: pancreatic inflammation (pancreas MPO activity and serum amylase) and pain (spinal cord fos expression in the dorsal horn at T8-10 with fos expression at T6 serving as an internal control). Some animals were pre-treated with the TRPV1 antagonist capsazepine (1.8 mg/kg intraperitoneal) to confirm the specificity of the effect. Results and Conclusions: Intrapancreatic injection of enterokinase significantly increased pancreatic inflammation as evidenced by elevated amylase and MPO as compared to vehicle controls (data not shown). Enterokinase increased pancreatic pain as evidenced by increased spinal cord fos expression at T8-10 as compared vehicle controls (Figure 1, p < 0.05). The effect was specific to the pancreas since there was no difference among groups at T6. Enterokinase-induced pancreatic nociception occurred via activation of TRPV1 since it was inhibited by capsazepine (Figure 2, p < 0.05 at T9,T10). From these findings we conclude that endogenous trypsin, which is released early in the course of acute pancreatitis, may play an important role in promoting pancreatic inflammatory pain via the activation of TRPV1.Figure: No Caption Available.Figure: No Caption Available.