Characterization of Two Classes of Pancreatic Shock Factors: Functional Differences Exhibited by Hydrophilic and Hydrophobic Shock Factors

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Abstract
Pancreatic tissue homogenate induces a powerful pathophysiologic response sufficient to produce lethal shock in a rat. However, limited progress has been made in the biochemical characterization of these pancreas-derived active factors or their mechanisms of action. It has been shown that the pancreas is a major source of these shock-inducing factors and that they are generated by pancreatic proteinases. Porcine pancreas was homogenized and the filtered homogenate was subjected to organic extraction both before and after incubation for 2.5 h at 37°C. The aqueous and lipid extracts of pancreatic homogenates were collected and analyzed for their ability to activate human neutrophils and to induce lethal shock in the rat. Neutrophil activation, a presumed hallmark of shock, was determined by chemiluminescence and myeloperoxidase (MPO) release. Only the intact homogenate and lipid extracts stimulated the neutrophils, and the aqueous extracts proved to be inactive. Neutrophils exhibited enhanced cellular activation when exposed to substimulatory levels of either formyl-methionyl-leucyl-phenylalanine (FMLP) or platelet-activating factor (PAF) followed by substimulatory levels of the lipid extracts, but not by the aqueous extracts. Both the lipid and aqueous extracts induced dramatic decreases in heart rate and blood pressure when injected in the rat, often resulting in lethal shock. In all cases, incubation of the homogenates at 37°C enhanced the potency of the extracts. Our results demonstrated that the pancreas-derived homogenate and lipid factors were capable of inducing both neutrophil activation and shock. These results support the hypothesis that shock is produced via neutrophils that have been activated by inflammatory components. However, the shock-inducing factors in the aqueous extracts (i.e., hydrophilic fraction of the homogenate) apparently function via a pathway independent of neutrophil activation. This is the first evidence that there are both hydrophobic and hydrophilic factors generated in tissue homogenates capable of inducing shock, and that these different chemical classes of factors appear to function via separate mechanisms.