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G Kieselbach, MT Kralinger, J Troger, J Hinterhoezl, R Fischer-Colbrie; Secretoneurin in the Rabbit Aqueous Humor . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3240.
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Purpose: Secretoneurin, a 33 amino acid neuropeptide, is generated by proteolytical processing of secretogranin II, which belongs to the chromogranin family. This study aimed to investigate, whether secretoneurin is present in the uninflamed rabbit aqueous humor and whether it is released in response to treatment with topical formaldehyde, an agent known to release sensory peptides originating from the trigeminal ganglion. Methods: Aqueous humor obtained by paracenthesis was analysed for secretoneurin-immunoreactivity in eyes pretreated with neutral formaldehyde and untreated controls by a highly sensitive radioimmunoassay. Furthermore, the molecular form of the secretoneurin-immunoreactivity was characterized by gel filtration high performance liquid chromatography (HPLC). Results: Secretoneurin-immunoreactivity was detected in moderate but significant amounts in the aqueous humor. The mean concentration of secretoneurin was 8.1 (0.34) fmol/100µl in controls and 7.8 (0.1) fmol/100µl 15 min after formaldehyde application. 30 min after treatment, the secretoneurin levels were significantly elevated by 63%. Gel filtration HPLC revealed that the main molecular form corresponded to the free peptide secretoneurin. Conclusion: The neuropeptide secretoneurin has been detected in the anterior segment of the eye for the first time. The concentrations in untreated specimens are about one tenth of those of the classical sensory peptide substance P and the elevation of secretoneurin in formaldehyde treated eyes is obviously realized by an enhanced release from the iris/ciliary body complex. As formaldehyde provokes neurogenic inflammation in the anterior segment exclusively via release of sensory peptides originating from the trigeminal ganglion, our results indicate a sensory origin of secretoneurin in the eye.
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