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Masakazu Yamada, Masaro Ogata, Masataka Kawai, Yukihiko Mashima, Teruo Nishida; Substance P and Its Metabolites in Normal Human Tears. Invest. Ophthalmol. Vis. Sci. 2002;43(8):2622-2625.
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purpose. 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 SP8-11 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.
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