title: Relaxin inhibits the activation of human neutrophils: involvement of the nitric oxide pathway.
abstract: In animal models of inflammation, the pregnancy hormone relaxin was shown to reduce the recruitment of leukocytes, especially neutrophils, in inflamed tissues. The current study was designed to clarify whether relaxin could inhibit activation of isolated human neutrophils and, if so, whether the nitric oxide (NO) biosynthetic pathway was involved, as occurs in other relaxin targets. Human neutrophils were preincubated with 1, 10, and 100 nmol/liter porcine relaxin for 1 h before activation with N-formyl-Met-Leu-Phe (10 micromol/liter) or phorbol-12-myristate-13-acetate (0.1 micromol/liter). In selected experiments, the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 100 micromol/liter) was added to the samples 30 min before relaxin. In other experiments, chemically inactivated relaxin (10 nmol/liter) was substituted for authentic relaxin. Untreated, nonactivated neutrophils were the controls. Relaxin reduced significantly and in a concentration-dependent fashion the expression of the surface activation marker CD11b, as well as the generation of superoxide anion, the rise of intracellular Ca(2+), the release of cytoplasmic granules, and the chemotactic migration. These effects of relaxin were blunted by N(G)-monomethyl-L-arginine and could not be reproduced by inactivated relaxin. Relaxin also increased neutrophil inducible NO synthase expression and NO generation. This study provides evidence that relaxin inhibits the activation of human neutrophils stimulated by different proinflammatory agents. This novel property of relaxin could be of relevance in toning down maternal neutrophil activation during pregnancy, thereby counteracting the occurrence of pregnancy-related disorders such as preeclampsia, which is regarded as an excess maternal inflammatory response to pregnancy.
authors: Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
authors: Emanuela
authors: E
authors: Masini
authors: Silvia
authors: S
authors: Nistri
authors: Alfredo
authors: A
authors: Vannacci
authors: Tatiana
authors: T
authors: Bani Sacchi
authors: Andrea
authors: A
authors: Novelli
authors: Daniele
authors: D
authors: Bani
mesh_terms: D002118:Calcium / Q000378:metabolism; D002273:Carcinogens / Q000494:pharmacology; D002634:Chemotaxis, Leukocyte / Q000187:drug effects / Q000276:immunology; D006801:Humans; D008854:Microscopy, Electron; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D009569:Nitric Oxide / Q000378:metabolism*; D012065:Relaxin / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002273:Carcinogens; D013481:Superoxides; D009569:Nitric Oxide; D009240:N-Formylmethionine Leucyl-Phenylalanine; D012065:Relaxin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium