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Juanita Carnes, Gianluca Tosini; Melatonin-Induced Reduction of Nitric Oxide Release and cGMP Production in Human Nonpigmented Ciliary Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3105.
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Melatonin is representative of a class of compounds that is proving to be effective in lowering IOP and, being a natural substance, is virtually side effect free. To date, however, the mechanisms by which melatonin and its analogues reduce IOP are not known. The present study was performed in order to examine the effect of melatonin on nitric oxide (NO) and cGMP signaling in aqueous humor producing nonpigmented ciliary epithelial (NPCE) cells.
NPCE cells were grown to 70 - 80% confluency on 12 or 6 well plates. Nitric oxide release protocols were carried out using cells treated in dye free DMEM containing protease inhibitor cocktail and L-arginine. cGMP experimental protocols were performed using dye free DMEM containing IBMX. The effects of melatonin (10-10 - 10-3 M) on basal or sodium nitroprusside (SNP, 100 mM) elevated NO or cGMP production were determined in separate experiments. NO and cGMP levels were measured using a colorimetric assay or enzyme immunoassay, respectively. Melatonin receptor selectivity was evaluated using luzindole (nonselective MT1/ MT2 antagonist) or 4-P-PDOT (selective MT2 antagonist).
Melatonin caused concentration-dependent reductions in basal and SNP elevated NO and cGMP production. Pretreatment with luzindole (10-5 M) or 4-phenyl-2-propionamidotetralin (4-P-PDOT, 10-7 M) inhibited melatonin-induced reduction in SNP released NO. Further studies are being conducted to determine the effect of the MT receptor antagonists on melatonin-induced changes in cGMP production.
Results from this study suggest that melatonin-induced suppression of nitridergic signaling in the anterior segment of the eye could play a role in its ocular hypotensive effect.
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