title: Detection of substance P in human tears by laser desorption mass spectrometry and immunoassay.
abstract: OBJECTIVE
  To determine whether substance P is present in human tears.
  
  
  METHODS
  Tear samples (1-2 microliters) were collected from one eye of each of 12 subjects. Two of the eyes had dry eye syndrome, two wore contact lenses and had dry eye syndrome, and eight were normal. Five of the eight normal eyes were scheduled to undergo excimer laser refractive surgery, and tears were collected from these eyes before and after surgery. Tear samples were analyzed by laser desorption mass spectrometry. Pooled samples from one individual were subjected to enzyme-linked immunoabsorbent assay.
  
  
  RESULTS
  Laser desorption mass spectra of the 18 tear samples displayed well defined peaks with mass to charge (m/z) ratios ranging from 1343.7 to 1355.9 and/or 1356.9 to 1364.7, corresponding to an average m/z of 1349.8 +/- 1.13 for protonated substance P and 1361.2 +/- 0.54 for oxidized substance P obtained from 14 mass spectra of standards formulated with substance P concentrations ranging from 10(-4) M to 10(-12) M. As confirmation, an enzyme-linked immunoabsorbent assay performed twice on pooled tears from one eye detected substance P in both replicates at a concentration of 125 pg/ml (9.26 x 10(-11) M).
  
  
  CONCLUSIONS
  These findings demonstrate that substance P is a component of tears obtained from normal eyes of men and women ranging in age from 26 to 60 years, from eyes fitted with contact lenses, from eyes with dry eye syndrome, and from eyes 1 and 2 days after excimer laser refractive surgery. Whether the concentration of substance P in tears varies with sex, age, or eye condition, the source of substance P in tears, and its role in tears remains to be discovered.
authors.affiliation: LSU Eye Center, Louisiana State University Medical Center, School of Medicine, New Orleans 70112, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Varnell
authors.forename: J Y
authors.initials: JY
authors.lastname: Freeman
authors.forename: D
authors.initials: D
authors.lastname: Maitchouk
authors.forename: R W
authors.initials: RW
authors.lastname: Beuerman
authors.forename: B M
authors.initials: BM
authors.lastname: Gebhardt
mesh_terms: D000328:Adult; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013373:Substance P / Q000378:metabolism*; D013666:Tears / Q000378:metabolism*
chemical_list: D013373:Substance P