Abdominal hyperalgesia in secretory phospholipase A 2-induced rat pancreatitis: Distinct roles of NK 1 receptors

Abstract

We investigated the potential of secretory phospholipase A 2 (sPLA 2)-induced pancreatitis to promote abdominal hyperalgesia, as well as to depolarize sensory fibres in vitro using a grease-gap technique. Pancreatitis was induced by the injection of sPLA 2 from Crotalus durissus terrificus (sPLA 2 Cdt, 300 μg kg −1) venom into the common bile duct of rats. Pancreatic inflammatory signs, serum amylase levels and abdominal hyperalgesia were evaluated in rats treated or not with SR140333, a tachykinin NK 1 receptor antagonist. Injection of sPLA 2 Cdt caused pancreatic oedema formation and increased pancreatic neutrophil infiltration and serum amylase at 4 h, which returned to normality by 24 h, except for the neutrophil infiltration, which was still increased at this time point. Animals injected with sPLA 2 exhibited a lower withdrawal threshold to electronic von Frey stimulation in the upper abdominal region at 4 h, but not 24 h, post-injection when compared with saline-injected rats. Pre-treatment of animals with SR140333 significantly reduced the sPLA 2 Cdt-induced abdominal hyperalgesia, without affecting the other parameters. Neither sPLA 2 Cdt nor sPLA 2 from Naja mocambique mocambique venom depolarized capsaicin-sensitive sensory fibres from rat vagus nerve, but they decreased the propagated compound action potentials in both A and C fibres. These data show for the first time that NK 1 receptors play an important role in the early abdominal hyperalgesia in a rat model of sPLA 2-induced pancreatitis, suggesting that these receptors are of importance in the development of pain in the pancreatitis condition. We also provide evidence that sPLA 2s do not directly depolarize sensory fibres in vitro.