We have described in det ail the secretory activity of leukotriene B4 toward rabbit neutrophils. Leukotriene B4 rapidly and vigorously degranulates rabbit neutrophils. This activity is stereospecific, cytochalasin B-dependent, and is enhanced by extracellular calcium. Pretreatment with leukotriene B4 deactivates rabbit neutrophils, i.e., cells so treated do not respond to stimulation by an additional bolus of leukotriene B4. In addition, the secretory activity of leukotriene B4 is sharply dependent on the simultaneous presence of cytochalasin B. Rabbit neutrophils therefore exhibit the previously described desensitization to the effect of cytochalasin B. In these and other discussed respects the characteristics of the leukotriene B4-induced degranulation of rabbit neutrophils are strikingly similar to those of the chemotactic factors. These results support the hypothesis that leukotriene B4 mediates, at least in part, the secretory, and possibly other, activities of chemotactic factors.

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