The effects of histamine and serotonin on polymorphonuclear leukocyte accumulation in the rat

Histamine and serotonin were evaluated for their effects on rat polymorphonuclear leukocyte (PMN) accumulation in vivo and PMN migration in vitro. Both of the mediators inhibited the accumulation of PMNs when injected into the pleural cavity in a saline vehicle, and reduced the PMN content of the peripheral blood. Histamine also reduced the cellular influx when administered in combination with an intrapleural injection of carrageenan. Peripheral blood leukocytes removed from rats injected intrapleurally with histamine and carrageenan had a lesser chemotactic responsiveness compared with those removed from rats injected only with carrageenan. The effects of histamine in reducing PMN accumulation was abolished by treatment with cimetidine, an H2 antagonist, but not by treatment with chlorpheniramine, an H1 antagonist. These results suggest that a local release of histamine may play a role in reducing cellular infiltration into an inflammatory site.