3 principal physiological effects (1)it is a mediator of inflammation(swelling) associated with the immune response (2)it is a chemical that stimulates secretion of gastric ac (3) it is a transmitter amine in both the peripheral and the central nervous systems3 principal physiological effects: (1) it is a mediator of inflammation (swelling) associated with the immune response (2) it is a chemical that stimulates secretion of gastric acid (3) it is a transmitter amine in both the peripheral and the central nervous systems