The chemoattractant formyl-methionine-leucine-phenylalanine (FMLP) has recently been shown to possess spasmogenic properties in smooth muscle preparations from various organs. In this study we have investigated the actions of this peptide on isolated rabbit pulmonary artery (PA) ring segments. FMLP stimulated concentration-dependent constriction of PA at resting tension. However, in PA that had been preconstricted by norepinephrine, FMLP stimulated concentration-dependent relaxation. FMLP-stimulated PA constriction was inhibited by earlier exposure to indomethacin or to furegrelate, a thromboxane synthetase inhibitor, but not by earlier exposure to the H1 histamine receptor antagonist pyrilamine. FMLP-stimulated relaxation of PA was totally abolished by indomethacin but not by furegrelate or pyrilamine. Disruption of the endothelium in PA preparations decreased both the constriction and relaxation response to the peptide, suggesting that these cells were involved in these responses. These results indicate that the chemotactic factor FMLP can elicit constriction or relaxation of isolated PA, depending on the underlying active PA tension. In addition, both constriction and relaxation are dependent on cyclooxygenase products and intact endothelium.
A synthetic peptide derivative that is a cholecystokinin receptor antagonist.