title: Plasma substance P levels in patients with persistent cough.
abstract: BACKGROUND
  Substance P (SP) is involved in the pathogenesis of cough in animal models. However, few studies in humans have been reported and the roles of SP in clinical cough remain obscure.
  
  
  OBJECTIVE
  To clarify the relevance of plasma levels of SP in patients with persistent cough.
  
  
  METHODS
  We studied 82 patients with cough persisting for at least 3 weeks and 15 healthy controls. Patients were classified as having asthmatic cough (cough-variant asthma and cough-predominant asthma; n = 61) or nonasthmatic cough (n = 21; postinfectious cough, n = 6; gastroesophageal reflux disease, n = 5; idiopathic cough, n = 5, and others, n = 5). Correlations were evaluated between plasma SP levels as measured with ELISA and methacholine airway hyperresponsiveness (airway sensitivity and airway reactivity), capsaicin cough sensitivity, sputum eosinophil and neutrophil counts, and pulmonary function.
  
  
  RESULTS
  Plasma SP levels were significantly elevated in patients with both asthmatic and nonasthmatic cough compared with controls [31.1 pg/ml (range 18.0-52.2) and 30.0 pg/ml (range 15.1-50.3) vs. 15.4 pg/ml (range 11.3-23.7); p = 0.003 and p = 0.038, respectively] but did not differ between the two patient groups (p = 0.90). Plasma SP levels correlated with airway sensitivity (threshold dose of methacholine) in the patients with asthmatic cough (r = -0.37, p = 0.005) but not with airway reactivity, cough sensitivity, FEV1 values, or sputum eosinophil and neutrophil counts in either group.
  
  
  CONCLUSIONS
  Increased levels of SP in plasma are associated with persistent cough in humans and might be related to airway sensitivity in asthmatic cough.
authors.affiliation: Department of Respiratory Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Kojiro
authors.initials: K
authors.lastname: Otsuka
authors.forename: Akio
authors.initials: A
authors.lastname: Niimi
authors.forename: Hisako
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Isao
authors.initials: I
authors.lastname: Ito
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Matsuoka
authors.forename: Makiko
authors.initials: M
authors.lastname: Jinnai
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Oguma
authors.forename: Tomoshi
authors.initials: T
authors.lastname: Takeda
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Nakaji
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chin
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Sasaki
authors.forename: Norihito
authors.initials: N
authors.lastname: Aoyama
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
mesh_terms: D000328:Adult; D000368:Aged; D001249:Asthma / Q000097:blood* / Q000150:complications / Q000503:physiopathology; D003371:Cough / Q000097:blood* / Q000209:etiology / Q000503:physiopathology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005764:Gastroesophageal Reflux / Q000097:blood* / Q000150:complications / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012129:Respiratory Function Tests; D013373:Substance P / Q000378:metabolism*
chemical_list: D013373:Substance P