Elevated levels of secretoneurin in the rabbit aqueous humor in response to formaldehyde irritation.
BACKGROUND
Secretoneurin, a 33-amino-acid neuropeptide, is generated by proteolytic 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
Blood samples and aqueous humor of eyes pretreated with neutral formaldehyde and untreated controls were analyzed for secretoneurin immunoreactivity by a highly sensitive radioimmunoassay. Furthermore, the molecular form of the secretoneurin immunoreactivity was characterized by gel filtration high-performance liquid chromatography (HPLC).


RESULTS
In the blood, secretoneurin levels were found to be below the detection limit of 2 fmol/100 microl. In the aqueous humor, secretoneurin-immunoreactivity was detected in moderate but significant amounts. The mean concentration of secretoneurin was 8.1 (+/-0.34) fmol/100 microl in controls and 7.8 (+/-0.1) fmol/100 microl 15 min after formaldehyde application. Thirty minutes 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.


CONCLUSIONS
The neuropeptide secretoneurin has been detected in the anterior segment of the eye for the first time. The elevation of secretoneurin in formaldehyde-treated eyes may be induced by an enhanced release from the iris/ciliary body complex, as formaldehyde is known to provoke neurogenic inflammation in the anterior segment via release of sensory peptides originating from the trigeminal ganglion. This is why our results indicate a sensory origin of secretoneurin in the eye.
Kralinger
Martina T
MT
Department of Ophthalmology and Optometry, University of Innsbruck, Anichstrasse 35, 6020 , Innsbruck, Austria. martina.kralinger@uibk.ac.at.
Hinterhölzl
Josef
J
Department of Pharmacology, University of Innsbruck, Austria.
Troger
Josef
J
Department of Ophthalmology and Optometry, University of Innsbruck, Anichstrasse 35, 6020 , Innsbruck, Austria.
Nguyen
Quynh Anh
QA
Department of Ophthalmology and Optometry, University of Innsbruck, Anichstrasse 35, 6020 , Innsbruck, Austria.
Kremser
Bernhard
B
Department of Ophthalmology and Optometry, University of Innsbruck, Anichstrasse 35, 6020 , Innsbruck, Austria.
Fischer-Colbrie
Reiner
R
Department of Pharmacology, University of Innsbruck, Austria.
Kieselbach
Gerhard F
GF
Department of Ophthalmology and Optometry, University of Innsbruck, Anichstrasse 35, 6020 , Innsbruck, Austria.
D000818:Animals; D001082:Aqueous Humor / Q000187:drug effects* / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005557:Formaldehyde / Q000494:pharmacology*; D007509:Irritants / Q000494:pharmacology*; D008297:Male; D009479:Neuropeptides / Q000097:blood / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011817:Rabbits; D011863:Radioimmunoassay; D053381:Secretogranin II
D007509:Irritants; D009479:Neuropeptides; D020033:Protein Isoforms; D053381:Secretogranin II; C081159:secretoneurin; D005557:Formaldehyde