title: Substance P in human tears.
abstract: OBJECTIVE
  To determine the levels and biochemical characteristics of substance P-like immunoreactivity (SPLI) in human tears and ascertain whether substance P (SP) concentrations in tears reflect the condition of the ocular surface.
  
  
  METHODS
  Unstimulated tears were collected with a micropipette. Tear samples were partially purified using C-18 cartridges. Levels of SPLI in purified samples were measured using an enzyme immunoassay (EIA). For biochemical characterization of SPLI, tear extracts were fractionated using high-performance liquid chromatography (HPLC); each fraction was then subjected to EIA. To determine the catabolism of SP in tears, synthetic SP was incubated in medium containing pooled tears and then analyzed using HPLC.
  
  
  RESULTS
  The concentration of SPLI in normal human tears was 306.0 +/- 96.5 pg/mL (mean +/- SD, range 148-555 pg/mL). Levels of SPLI did not vary significantly by age or gender. Concentrations of SPLI in tears from eyes with unilateral corneal hypesthesia were lower than those in tears from contralateral healthy eyes. Diclofenac sodium eye drops reduced concentrations of prostaglandin E2 and SPLI in tears. Analysis using HPLC indicated that five different substances contributed to SPLI in tears and that SP was broken down into several fragments, including SP(8-11), by enzymes present in tears.
  
  
  CONCLUSIONS
  Substance P is a normal component of human tears. Levels of SPLI in tears might reflect the denervated status of the ocular surface. Substance P is catabolized by degradative enzymes in tears to maintain the ocular surface by exerting the trophic effects of SP while avoiding undesirable effects.
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: D000287:Administration, Topical; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002851:Chromatography, High Pressure Liquid; D003316:Corneal Diseases / Q000378:metabolism*; D004008:Diclofenac / Q000008:administration & dosage; D004798:Enzymes / Q000378:metabolism; D005260:Female; D006801:Humans; D006987:Hypesthesia / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D013373:Substance P / Q000378:metabolism*; D013666:Tears / Q000201:enzymology / Q000378:metabolism*
chemical_list: D004798:Enzymes; D004008:Diclofenac; D013373:Substance P