A serial histologic study of the development and progression of acute pancreatitis in the rat.

This study was undertaken for the purpose of a serial investigation of the development and progression of the light-microscopic changes of acute pancreatitis and histologic criteria for evaluating pancreatitis. Acute pancreatitis, similar to that found in man, was induced in rats with the use of a closed duodenal loop technique (n = 36). Control rats underwent a laparotomy with mobilization of the duodenum (n = 12). Animals were killed every 2 hours for 24 hours, and a detailed and independent histologic evaluation was made of each. Focal acinar necrosis proceeding to a vasculitis appeared within 2--4 hours before the infiltration of inflammatory cells. Thereafter, the extent of acinar necrosis closely reflected the vasculitis with the later development of the acute inflammation. By the sixteenth hour, these changes were graded as moderate pancreatitis, and by 24 hours the process represented severe hemorrhagic pancreatitis. Vascular changes and acinar necrosis preceded the inflammatory cell infiltrate. The pancreatitis has been quantitated into minimal, moderate, or severe by assessing the severity of edema, acute inflammatory infiltrate, and changes in the vessels, ducts, and acini.