title: Substance P and its metabolites in normal human tears.
abstract: OBJECTIVE
  To determine amounts and biochemical characteristics of substance P-like immunoreactivity (SPLI) in tears of normal human subjects.
  
  
  METHODS
  Forty-three healthy subjects (16 males and 27 females; age range, 17-80 years) participated. Ten microliters of unstimulated tears were collected with a micropipette from one eye of all subjects. Tear samples were partially purified by C-18 cartridges. SPLI concentrations in purified samples were measured by enzyme immunoassay (EIA). For biochemical characterization of SPLI, tear extracts were fractionated by high-performance liquid chromatography (HPLC). Each fraction then was subjected to EIA. To determine the metabolism of substance P in tears, synthetic substance P was incubated in medium containing pooled tears and then analyzed by HPLC with the detector set at a 210-nm wavelength.
  
  
  RESULTS
  The SPLI concentration in normal human tears was 306.0 +/- 96.5 pg/mL (mean +/- SD; range, 148-555 pg/mL). SPLI did not significantly vary by age or gender. HPLC analysis indicated that SPLI in tears consisted of five different substances and that substance P was converted to several fragments, including SP(8-11) by enzymes present in tears.
  
  
  CONCLUSIONS
  Substance P, a normal component of human tears, presumably is released from the nerve endings in the ocular surface and converted to fragments by degradative enzymes in tears.
authors.affiliation: Department of Ophthalmology, Keio University School of Medicine, Tokyo, Japan. yamadam@sc.itc.keio.ac.jp
authors.forename: Masakazu
authors.initials: M
authors.lastname: Yamada
authors.forename: Masaro
authors.initials: M
authors.lastname: Ogata
authors.forename: Masataka
authors.initials: M
authors.lastname: Kawai
authors.forename: Yukihiko
authors.initials: Y
authors.lastname: Mashima
authors.forename: Teruo
authors.initials: T
authors.lastname: Nishida
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000032:analysis; D013373:Substance P / Q000032:analysis*; D013666:Tears / Q000737:chemistry*
chemical_list: D010446:Peptide Fragments; D013373:Substance P