Activated neutrophils inhibit cerebrovascular endothelium-dependent relaxations in vitro

The effect of formyl-Met-Leu-Phe- (fMLP-) activated feline neutrophil granulocytes on endothelium-dependent and independent relaxations was studied in the middle cerebral artery of the cat in vitro. Endothelium-dependent relaxations caused by acetylcholine and ATP were markedly inhibited after 30 minutes of incubation of the vessels with neutrophils (5000 cells/μl) in the presence of 5 μM fMLP, followed by a replacement of the bath solution in order to remove the neutrophils from the medium. Direct vasorelaxations in response to the nitric oxide donor compound SIN-1, however, remained unchanged. Both neutrophils and fMLP caused transient contractions during the incubation period. The present study provides direct evidence for the ability of activated neutrophils to cause an inhibition of vascular endothelium-dependent responses in vitro.