The effect of apelin on the functions of peritoneal macrophages.

Apelin, the endogenous ligand of the G protein-coupled receptor (APJ), plays an important role in the physiological response to homeostatic perturbations. The aim of the present study was to investigate the effect of apelin on the functions of peritoneal macrophages. A double staining immunofluorescence technique was used to determine the expression of APJ in peritoneal macrophages. Rat peritoneal macrophages were randomly divided into three groups: control, apelin and apelin+F13A. A significant decrease in phagocytic and chemotactic activity of peritoneal macrophages resulted when the macrophages were incubated with [Pry(1)]-Apelin-13 (10 ng/ml). Incubation of peritoneal macrophages with the APJ receptor antagonist, F13A (20 ng/ml) prevented the suppressive effect of apelin on phagocytosis and chemotaxis. Peritoneal macrophages incubated with [Pry(1)]-Apelin-13 exhibited a decrease in the production of TNF-alpha and IL-6 compared to the control macrophages. Incubation of peritoneal macrophages with [Pry(1)]-Apelin-13 plus F13A prevented the decrease in the production of proinflammatory cytokines produced by [Pry(1)]-Apelin-13. In conclusion, apelin may be a mediator that inhibits the functions of activated macrophages.