Neuropeptides and inflammation. A somatostatin analog as a selective antagonist of neutrophil activation by substance P

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Abstract
Objective. Substance P and somatostatin are neuropeptides found in peripheral sensory nerves. In vitro, these have opposing effects on inflammatory cells. We compared the effects of these peptides on the activation of neutrophils. Methods. Neutrophils were isolated from healthy volunteers, and chemotaxis, superoxide anion generation, aggregation, and changes in cytosolic calcium and GTPase activity were measured in the presence of substance P, somatostatin, and the chemoattractant FMLP. Results. Substance P was an effective chemoattractant, 20% as potent as FMLP at equimolar concentrations. Substance P also stimulated GTPase activity in neutrophil plasma membranes. Somatostatin did not activate neutrophils; however, it effectively inhibited neutrophil chemotaxis and GTPase activity provoked substance P, but not by FMLP. Conclusions. These studies demonstrate that substance P can effectively stimulate chemotaxis, possible via effects on a GTP-binding protein distinct from that triggered by FMLP, and that somatostatin is a selective antagonist of substance P. The biochemical specificities of these peptides on cells may modulate neurogenic inflammation at the local level.

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