The mechanism of histamine release induced by pilocarpine from different tissues: studies on rat peritoneal mast cells.

Pilocarpine releases histamine from mast cells of cat submandibular gland and rat liver. In the salivary gland, histamine is released into the saliva and venous outflow. Atropine blocks the salivation, but not histamine release from the submandibular gland into the blood. Histamine release from the gland could be due to a direct action of pilocarpine on tissue mast cells or to an indirect action of mediators (acetylcholine and peptides). These hypotheses were further investigated in our present studies on rat peritoneal mast cells. Our results show: (1) histamine release from rat peritoneal mast cells induced by pilocarpine (ED50 = 1.7 x 10(-2) mol/l) occurs at 1000-fold higher concentrations than by substance P (ED50 = 1.7 x 10(-5) mol/l) and in 6.5-fold higher concentrations than by atropine (ED50 = 2.6 x 10(-3) mol/l), (2) pilocarpine injected directly into the rat peritoneal cavity causes histamine release from peritoneal mast cells in 1.8-fold higher concentrations than from isolated rat peritoneal mast cells. These results would support the hypothesis that histamine release from cat submandibular gland is caused by peptidergic co-transmission during the stimulation of the organ.