Release of a neutrophil‐derived vascoconstrictor agent which augments platelet‐induced contractions of blood vessels in vitro

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Abstract
1 The effects of neutrophil-derived products on vascular tone in vitro were examined by adding purified rabbit neutrophils to siliconized organ baths containing rings of rabbit thoracic aorta. 2 Neutrophil-derived products induced a concentration-dependent contraction of the blood vessels generating 3.9 ± 0.2 g of tension at a cell concentration of 2 × 106 ml−1. This contractile response was not dependent on an intact endothelium and was not ameliorated by treatment of the neutrophils with inhibitors of lipoxygenase or cyclo-oxygenase enzymes, by free radical scavengers or by the use of end organ antagonists to angiotensin II, desArg9-bradykinin, histamine, catecholamines or acetylcholine. 3 Neutrophils stimulated with phorbol myristate acetate, formyl methionyl-leucyl-phenylalanine or calcium ionophore A23187 released a contractile factor into the supernatant which produced qualitatively similar contractions compared to those elicited by incubation with intact unstimulated neutrophils. 4 Ten to twenty times more platelets were required to evoke equivalent contractions to those observed with neutrophils. However, neutrophil supernates significantly augmented platelet-mediated contractions (P < 0.001). 5 Contractions elicited by neutrophils and supernates derived from activated neutrophils were partially antagonized by 5-hydroxytryptamine (5-HT) receptor antagonists, methysergide and ketanserin. However, the inhibition of exogenous 5-HT-induced contractions on rabbit aorta and rat stomach strips by both antagonists was greater than the inhibition of contractions produced by neutrophils and neutrophil-derived supernates. 6 Extraction of the biologically active material from supernatants of activated neutrophils into acetone, but not chloroform-methanol or ethyl acetate, suggests the contractile factor may be a protein/peptide. Partial purification on a Sephadex G100 column yields a contractile factor with a molecular weight of less than 4,000 daltons. 7 This factor may augment vascular tone, either directly or by interactions with platelets, in pathophysiological states associated with neutrophil activation and accumulation.