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M. Yamada, M. Ogata, K. Kumagai, Y. Mashima; Decreased Substance P Concentrations in Tears from Patients with Diabetes Mellitus . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2458.
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Purpose Corneal sensory nerve dysfunction, which may result in a decrease of axonally transported neuropeptides including substance P, is assumed to be involved in the mechanisms of diabetic keratopathy. We investigated whether substance P concentrations in tears reflect corneal hypoesthesia in patients with diabetes mellitus. Methods Forty-eight patients (29 men and 19 women ranging in age from 31 to 80 years) with diabetes mellitus participated in this study. Thirty-five normal subjects served as normal controls. All subjects gave informed consent for participation. Ten microliters of unstimulated tears were collected with a micropipette in one eye of all subjects. The tear samples were diluted 5 fold with 4% acetic acid and loaded onto C-18 cartridges. After washing with 4% acetic acid, samples were eluted with ethanol:water:acetic acid (90:10:0.04, v/v/v). Substance P concentrations in purified samples were measured using an enzyme immunoassay. Results The mean concentration of substance P in tears of diabetic patients was 220.2±86.6 pg/mL, which was significantly lower than those of normal controls (296.7±76.4 pg/mL). Substance P concentrations in tears of diabetic patients were not significantly associated with the degree of corneal hypesthesia, but correlated instead with the severity of diabetic retinopathy and the usage of insulin. Conclusions Substance P concentrations in tears of diabetic patients were lower than those of normal subjects. Decreased substance P in tears of diabetic patients may reflect the sensory nerve dysfunction in diabetes mellitus.
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