Substance P, acting via the neurokinin 1 receptor (NK1R), plays an important role in mediating a variety of inf lammatory processes. However, its role in acute pancreatitis has not been previously described. We have found that, in normal mice, substance P levels in the pancreas and pancreatic acinar cell expression of NK1R are both increased during secretagogue-induced experimental pancreatitis. To evaluate the role of substance P, pancreatitis was induced in mice that genetically lack NK1R by administration of 12 hourly injections of a supramaximally stimulating dose of the secretagogue caerulein. During pancreatitis, the magnitude of hyperamylasemia, hyperlipasemia, neutrophil sequestration in the pancreas, and pancreatic acinar cell necrosis were significantly reduced in NK1R؊͞؊ mice when compared with wild-type NK1R؉͞؉ animals. Similarly, pancreatitisassociated lung injury, as characterized by intrapulmonary sequestration of neutrophils and increased pulmonary microvascular permeability, was reduced in NK1R؊͞؊ animals. These effects of NK1R deletion indicate that substance P, acting via NK1R, plays an important proinf lammatory role in regulating the severity of acute pancreatitis and pancreatitisassociated lung injury.The neuropeptide substance P has been shown to play an important role in asthma, inflammatory bowel disease, arthritis, and other inflammatory processes (1, 2). Subsequent to its release from nerve endings, substance P binds to neurokinin 1 receptors (NK1R) on effector cells, increases microvascular permeability, and promotes plasma extravasation from the intravascular to the extravascular space. Although pancreatic acinar cells are known to express NK1R and substance P has been detected within the pancreas (3-5), apparently no studies have been reported that have examined the possibility that this neuropeptide might play a role in the evolution of a pancreatic inflammatory disease such as acute pancreatitis. We have found that pancreatic levels of substance P and the expression of NK1R on pancreatic acinar cells are increased during experimental acute pancreatitis. We have also found that genetic deletion of NK1R reduces the severity of pancreatitis and pancreatitis-associated lung injury. These observations indicate that substance P, acting through NK1R, plays an important proinflammatory role in regulating the severity of acute pancreatitis and associated lung injury. MATERIALS AND METHODSAll experiments were performed according to protocols approved by the Institutional Animal Care and Use Committee of the Beth Israel Hospital. Breeding pairs of NK1R-deficient mice were generated as described (6), and the identity of their offspring as NK1R-deficient (Ϫ͞Ϫ) homozygotes was confirmed by Southern blotting (6). Animals were bred and housed in standard shoe box cages in a climate-controlled room with an ambient temperature of 23 Ϯ 2°C and a 12-h light͞12-h dark cycle. They were fed standard laboratory chow, given water ad libitum, randomly assigned to control or experimental groups, and...

Supramaximal stimulation of the pancreas with the CCK analog caerulein causes acute edematous pancreatitis. In this model, active trypsin can be detected in the pancreas shortly after the start of supramaximal stimulation. Incubation of pancreatic acini in vitro with a supramaximally stimulating caerulein concentration also results in rapid activation of trypsinogen. In the current study, we have used the techniques of subcellular fractionation and both light and electron microscopy immunolocalization to identify the site of trypsinogen activation and the subsequent fate of trypsin during caerulein-induced pancreatitis. We report that trypsin activity and trypsinogen-activation peptide (TAP), which is released on activation of trypsinogen, are first detectable in a heavy subcellular fraction. This fraction is enriched in digestive enzyme zymogens and lysosomal hydrolases. Subsequent to trypsinogen activation, both trypsin activity and TAP move to a soluble compartment. Immunolocalization studies indicate that trypsinogen activation occurs in cytoplasmic vacuoles that contain the lysosomal hydrolase cathepsin B. These observations suggest that, during the early stages of pancreatitis, trypsinogen is activated in subcellular organelles containing colocalized digestive enzyme zymogens and lysosomal hydrolases and that, subsequent to its activation, trypsin is released into the cytosol.

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